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at 22:57:41 ut, the swift burst alert telescope (bat) triggered and located grb 200716c (trigger=982707). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 196.013, +29.630 which is ra(j2000) = 13h 04m 03s dec(j2000) = +29d 37' 47" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 10 sec. the peak count rate was ~30000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 22:59:04.2 ut, 82.9 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 196.0100, 29.6465 which is equivalent to: ra(j2000) = 13h 04m 2.40s dec(j2000) = +29d 38' 47.4" with an uncertainty of 6.6 arcseconds (radius, 90% containment). this location is 60 arcseconds from the bat onboard position, within the bat error circle. no event data are yet available to determine the column density using x-ray spectroscopy. the initial flux in the 0.1 s image was 1.10e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 93 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 13:04:02.43 = 196.01011 dec(j2000) = +29:38:40.6 = 29.64460 with a 90%-confidence error radius of about 0.75 arc sec. this position is 6.85 arc sec. from the center of the xrt error circle. the estimated magnitude is 16.34 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.01. burst advocate for this burst is t. n. ukwatta (tilan.ukwatta at gmail.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200716c: swift detection of a burst with an optical counterpart |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 190731a (ohno et al. gcn circ. 25244), collecting 5.0 ks of photon counting (pc) mode data between t0+33.4 ks and t0+62.9 ks. eleven uncatalogued x-ray sources are detected, of which one ("source 1") is fading with 3-sigma significance, and is therefore likely the grb afterglow. using 1953 s of pc mode data and 4 uvot images, we find an enhanced xrt position (using the xrt-uvot alignment and matching uvot field sources to the usno-b1 catalogue): ra, dec = 339.72015, -76.57744 which is equivalent to: ra (j2000): 22h 38m 52.84s dec(j2000): -76d 34' 38.8" with an uncertainty of 2.2 arcsec (radius, 90% confidence). this position is 4.0 arcmin from the fermi/lat position. the light curve can be modelled with a power-law decay with a decay index of alpha=1.3 (+0.6, -0.7). a spectrum formed from the pc mode data can be fitted with an absorbed power-law with a photon spectral index of 2.5 (+/-0.5). the best-fitting absorption column is 5.9 (+2.8, -2.2) x 10^21 cm^-2, in excess of the galactic value of 9.8 x 10^20 cm^-2 (willingale et al. 2013). the counts to observed (unabsorbed) 0.3-10 kev flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (7.8 x 10^-11) erg cm^-2 count^-1. a summary of the pc-mode spectrum is thus: total column: 5.9 (+2.8, -2.2) x 10^21 cm^-2 galactic foreground: 9.8 x 10^20 cm^-2 excess significance: 3.6 sigma photon index: 2.5 (+/-0.5) if the light curve continues to decay with a power-law decay index of 1.3, the count rate at t+24 hours will be 0.015 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 kev flux of 4.9 x 10^-13 (1.2 x 10^-12) erg cm^-2 s^-1. the results of the xrt-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/too_grbs/00020914/source1.php. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00020914. this circular is an official product of the swift-xrt team. | grb 190731a: swift-xrt afterglow detection |
at 20:15:42 ut, the swift burst alert telescope (bat) triggered and located possible grb 180510b (trigger=831816). due to an observing constraint swift did not slew immediately to the burst. the bat on-board calculated location is ra, dec 77.989, -62.335 which is ra(j2000) = 05h 11m 57s dec(j2000) = -62d 20' 05" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 20 sec. the peak count rate was ~800 counts/sec (15-350 kev), at ~5 sec after the trigger. the xrt began observing the field at 21:04:52.4 ut, 2950.1 seconds after the bat trigger. using promptly downlinked data we find a fading, uncatalogued x-ray source located at ra, dec 77.96962, -62.32356 which is equivalent to: ra(j2000) = 05h 11m 52.71s dec(j2000) = -62d 19' 24.8" with an uncertainty of 3.6 arcseconds (radius, 90% containment). this location is 52 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (2.54 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 4.8 (+3.31/-2.67) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 2953 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 05:11:52.64 = 77.96932 dec(j2000) = -62:19:26.3 = -62.32396 with a 90%-confidence error radius of about 0.76 arc sec. this position is 4.0 arc sec. from the center of the xrt error circle. the estimated magnitude is 18.25 with a 1-sigma error of about 0.15. no correction has been made for the expected extinction corresponding to e(b-v) of 0.03. burst advocate for this burst is a. tohuvavohu (aaronb at swift.psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/too.html.) | grb 180510b: swift detection of a burst with an optical counterpart |
at 14:36:06 ut, the swift burst alert telescope (bat) triggered and located grb 191017b (trigger=929981). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 245.151, -73.561 which is ra(j2000) = 16h 20m 36s dec(j2000) = -73d 33' 40" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a single-peaked structure with a duration of about 8 sec. the peak count rate was ~1000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 14:37:50.7 ut, 103.8 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 245.1255, -73.5404 which is equivalent to: ra(j2000) = 16h 20m 30.13s dec(j2000) = -73d 32' 25.3" with an uncertainty of 2.2 arcseconds (radius, 90% containment). this location is 78 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (9.84 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 3 (+3.00/-2.59) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 301 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.11. burst advocate for this burst is b. sbarufatti (bxs60 at psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 191017b: swift detection of a burst |
many of the most energetic phenomena in the universe can be seen by radio telescopes and are transient in nature. recent scientific and technological advancements have enabled the breakthrough detections of two new types of exciting transient: fast radio bursts (frbs) and neutron star mergers. this thesis focuses on devising new observational strategies for these two young topics, and exploring possible connections between them. what causes frbs is not known. some frb sources repeat by emitting multiple times, whereas most are only observed to emit once. a highly debated question is whether there are multiple types of frb, or whether they all have the same physical explanation. part of this thesis explores this question, focusing on observations of the oldest known repeating frb (ch. 2) and comparing observations of other frbs to models related to neutron star mergers (ch. 3). we devise a new strategy using the low-frequency array (lofar) to catch coherent radio emission, like frbs, immediately following a gamma-ray burst/neutron star merger and provide the deepest limits yet (ch. 4 & 5). we also look at the elusive longer lasting synchrotron radio afterglow known to follow binary neutron star mergers. we use lofar to study gw170817, the only merger radio afterglow ever to be associated with detected gravitational waves (ch. 6). such radio afterglows are encoded with rich high-energy physics but are difficult to find owing to their poorly constrained locations. we develop a lofar strategy in ch. 7 that will enable us to probe the full location uncertainty region in the next gravitational wave observing run. | fast radio bursts and the radio counterparts of neutron star mergers |
at 02:00:27 ut, the swift burst alert telescope (bat) triggered and located grb 210210a (trigger=1031728). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 262.811, +14.648 which is ra(j2000) = 17h 31m 15s dec(j2000) = +14d 38' 53" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). due to a telemetry gap, only the first 8 seconds of the bat light curve after the trigger are available, showing that the emission has at least two peaks and continues beyond that time. the peak count rate was ~6000 counts/sec (15-350 kev), at ~4 sec after the trigger. the xrt began observing the field at 02:01:50.0 ut, 82.1 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 262.77059, 14.66385 which is equivalent to: ra(j2000) = 17h 31m 04.94s dec(j2000) = +14d 39' 49.9" with an uncertainty of 3.5 arcseconds (radius, 90% containment). this location is 151 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (8.82 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 2.2 (+1.27/-1.18) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 85 seconds after the bat trigger. there is a candidate afterglow in the list of sources generated on-board at ra(j2000) = 17:31:05.00 = 262.77085 dec(j2000) = +14:39:45.8 = 14.66272 with a 90%-confidence error radius of about 1.10 arc sec. this position is 4.6 arc sec. from the center of the xrt error circle. the estimated magnitude is 17.06. no correction has been made for the expected extinction corresponding to e(b-v) of 0.097. burst advocate for this burst is s. laha (sib.laha at gmail.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210210a: swift detection of a burst with an optical counterpart |
at 06:47:17 ut, the swift burst alert telescope (bat) triggered and located grb 200509a (trigger=970886). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 116.450, -4.641 which is ra(j2000) = 07h 45m 48s dec(j2000) = -04d 38' 28" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 20 sec. there is also possible further activity for several hundred seconds the peak count rate was ~1400 counts/sec (15-350 kev), at ~4 sec after the trigger. the xrt began observing the field at 06:49:16.9 ut, 119.6 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 116.42333, -4.63131 which is equivalent to: ra(j2000) = 07h 45m 41.60s dec(j2000) = -04d 37' 52.7" with an uncertainty of 3.5 arcseconds (radius, 90% containment). this location is 101 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (1.58 x 10^21 cm^-2, willingale et al. 2013), with an excess column of 5.2 (+4.12/-3.39) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of nominal 150.000 seconds with the white filter starting 123 seconds after the bat trigger. there is a candidate afterglow in the list of sources generated on-board at ra(j2000) = 07:45:41.20 = 116.42166 dec(j2000) = -04:37:49.4 = -4.63040 with a 90%-confidence error radius of about 1.10 arc sec. this position is 6.4 arc sec. from the center of the xrt error circle. the estimated magnitude is 19.15. no correction has been made for the expected extinction corresponding to e(b-v) of 0.13. the 2.7'x2.7' sub-image does not cover the region of this potential counterpart. burst advocate for this burst is e. troja (eleonora.troja at nasa.gov). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200509a: swift detection of a burst with a possible optical counterpart |
at 12:59:59.42 ut, the swift burst alert telescope (bat) triggered and located grb 190828b (trigger=922808). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 251.818, 27.237 which is ra(j2000) = 16h 47m 16s dec(j2000) = +27d 14' 12" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 40 sec. the peak count rate was ~3000 counts/sec (15-350 kev), at ~10 sec after the trigger. the xrt began observing the field at 13:00:54.1 ut, 54.7 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source with an enhanced position: ra, dec 251.8317, 27.2808 which is equivalent to: ra(j2000) = 16h 47m 19.60s dec(j2000) = +27d 16' 50.9" with an uncertainty of 2.2 arcseconds (radius, 90% containment). this location is 163 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 6.84 x 10^20 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 2.12e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 63 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.10. burst advocate for this burst is s. dichiara (dichiara at umd.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 190828b: swift detection of a burst |
the optical afterglow (atel #12824; gcn #24680; gcn #24684; gcn #24686; gcn #24687; gcn #24688; gcn #24690; gcn #24693; gcn #24697; gcn #24698; gcn #24700; gcn #24703; gcn #24708) of the bright grb 190530a (gcn #24676, gcn #24677; gcn #24679; gcn #24678, gcn #24683) is marginally detected on the stacked sloan-r band ccd frames (total exposure time 45 min) taken with the 0.8m rc80 telescope at konkoly observatory, piszkesteto (hungary) on 2019-05-31.35 ut, 1.42 day after the burst. | photometry of the optical afterglow of grb 190530a |
at 19:13:38 ut, the swift burst alert telescope (bat) triggered and located grb 221027b (trigger=1131397). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 225.603, +47.448 which is ra(j2000) = 15h 02m 25s dec(j2000) = +47d 26' 53" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 15 sec. the peak count rate was ~2000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 19:15:44.9 ut, 126.2 seconds after the bat trigger. using promptly downlinked data we find a fading, uncatalogued x-ray source with an enhanced position: ra, dec 225.62105, 47.44193 which is equivalent to: ra(j2000) = 15h 02m 29.05s dec(j2000) = +47d 26' 30.9" with an uncertainty of 1.9 arcseconds (radius, 90% containment). this location is 49 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (2.88 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 2.4 (+1.76/-1.55) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 130 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.033. burst advocate for this burst is a. y. lien (yarleen at gmail.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 221027b: swift detection of a burst |
swift-xrt has performed follow-up observations of the swift/bat-guano-detected burst grb 221215a, collecting 2.8 ks of photon counting (pc) mode data between t0+97.3 ks and t0+113.8 ks. no x-ray sources have been detected consistent with being within 296 arcsec of the swift/bat-guano position. the 3-sigma upper limit in the field is 0.005 ct s^-1, corresponding to a 0.3-10 kev observed flux of 1.9e-13 erg cm^-2 s^-1 (assuming a typical grb spectrum). an uncatalogued was detected, however this was too far from the grb position to be the afterglow. the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/00021533. this circular is an official product of the swift-xrt team. | grb 221215a: swift-xrt observations |
at 14:49:24 ut, the swift burst alert telescope (bat) triggered and located sgr 1830-0645 or grb 201010a (trigger=999571). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 277.675, -6.758, which is ra(j2000) = 18h 30m 42s dec(j2000) = -06d 45' 30" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve shows a single peak structure with a duration of no more than 0.128 sec. the peak count rate was ~1600 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 14:50:30.9 ut, 67.0 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 277.6702, -6.7550 which is equivalent to: ra(j2000) = 18h 30m 40.85s dec(j2000) = -06d 45' 18.0" with an uncertainty of 2.2 arcseconds (radius, 90% containment). this location is 20 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 1.11 x 10^22 cm^-2 (willingale et al. 2013). uvot took a finding chart exposure of 150 seconds with the white filter starting 71 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. no correction has been made for the large, but uncertain, extinction expected. due to its short duration (bat trigger duration of 8 ms, although the immediately available lightcurve is only available at 128 ms resolution), the soft spectrum (not visible above 50 kev) and its location in the galactic bulge near the plane (lon,lat) = (24.5, 1.5) we suspect that this event may be a new soft gamma repeater, which we would name sgr 1830-0645. burst advocate for this burst is k. l. page (klp5 at leicester.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | swift detection of a new sgr 1830-0645 or a short grb 201010a |
at 09:22:50 ut, the swift burst alert telescope (bat) triggered and located grb 220926a (trigger=1125354). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 245.011, -16.043 which is ra(j2000) = 16h 20m 03s dec(j2000) = -16d 02' 32" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 40 sec. the peak count rate was ~400 counts/sec (15-350 kev), at ~5 sec after the trigger. the source is not well identified in the rate data which is typical of an image trigger. the xrt began observing the field at 09:25:04.4 ut, 134 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 245.0022, -16.0438 which is equivalent to: ra(j2000) = 16h 20m 0.53s dec(j2000) = -16d 02' 37.7" with an uncertainty of up to 2 arcmin (radius, 90% containment). given the star tracker loss of lock at the time of the trigger, it is unclear how accurate this localisation is, hence the large uncertainty listed. no event data are yet available to determine the column density using x-ray spectroscopy. uvot took a finding chart exposure of 150 seconds with the white filter starting 143 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image processing failed because of no aspect solution. results from the list of sources generated on-board are not available at this time. no correction has been made for the expected extinction corresponding to e(b-v) of 0.269. note that this trigger occurred during an interval when the star trackers had lost lock. however, we believe this to be a real grb. burst advocate for this burst is m. j. moss (mikejmoss3 at gmail.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 220926a: swift detection of a burst |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 210704a (berretta et al. gcn circ. 30375), collecting 2.6 ks of photon counting (pc) mode data between t0+53.5 ks and t0+61.1 ks. an uncatalogued x-ray source is detected and is above the 2sxps 3-sigma upper limit at this position, and is therefore likely the grb afterglow. using 2378 s of pc mode data and 2 uvot images, we find an enhanced xrt position (using the xrt-uvot alignment and matching uvot field sources to the usno-b1 catalogue): ra, dec = 159.02219, +57.21636 which is equivalent to: ra (j2000): 10h 36m 05.33s dec(j2000): +57d 12' 58.9" with an uncertainty of 3.2 arcsec (radius, 90% confidence). this position is 5.9 arcmin from the fermi/lat position. we cannot determine at the present time whether the source is fading. the results of the xrt-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021454. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021454. this circular is an official product of the swift-xrt team. | grb 210704a: swift-xrt afterglow detection |
short-duration gamma-ray bursts (grbs) are brief flashes of high-energy emission lasting less than two seconds. these events have long been hypothesized to occur when two neutron stars spiral in and collide, launching enormously powerful jets of light and matter. can we now definitively make this connection?a singular event?artists illustration of a gamma-ray burst. could short gamma-ray bursts all be the product of neutron-star mergers? [nasa/swift/mary pat hrybyk-keith/john jones]in 2017, the ligo/virgo gravitational-wave detectors made the first observations of two neutron stars merging, in a chirp of ringing spacetime known as gw170817. just 1.7 seconds thereafter, scientists spotted a weak, short-duration gamma-ray burst coming from the same part of the sky, now labeled as grb170817a.in the ensuing months and years, weve carefully analyzed the data supplied by this event, attempting to understand what makes this grb light curve look the way it does. while gw170817s gamma-ray emission shares some traits with the known population of observed short grbs, it has a number of weird quirks.gw170817s host galaxy lies much closer than that of any other short grb known, and its gamma-ray energies were perhaps 10,000 times lower than is typical among the short grb population. grb170817as afterglow a long-lived glow that normally follows right after the initial gamma-ray flash of a grb only showed up 9 days after the flash.so is the outflow from gw170817 actually the same as that in other short grbs? and if so, does this mean that all short grbs arise from neutron-star mergers?angles matterto address these questions, new york university scientists yiyang wu and andrew macfadyan explored the structure of gw170817s outflow in comparison with a sample of 27 observed short grbs. the authors modeled the grb light curves allowing for a range of outflow structures from spherical flows that splay out in all directions, to jetted structures that are tightly beamed in a specific direction.from their fits, wu and macfadyan showed that the differences between grb170817as light curve and those of the other grbs can all be explained by one thing: viewing angle.plot of the viewing angle vs. opening angle for the jets of 17 known short grbs and gw170817. while all have similar opening angles, gw170817 is the only one viewed significantly off-axis. [wu macfadyan 2019]grb170817a and all the other grbs were found to be best fit by similar models with fast-moving jet-like structures, where the jet itself is extremely narrow: less than 10 wide. but according to wu and macfadyans fits, the normal grbs are viewed from an angle of 06 off the axis of the jet which means were looking nearly straight down the jet. for gw170817, however, were seeing the jet off-axis, from an angle of about 30.complications from relativitywhy does viewing angle matter? since these outflows are moving at nearly the speed of light, relativistic effects come into play. this means that energies and timescales can all look different depending on whether were viewing the jet on-axis or off-axis.if gw170817 and the other grbs can indeed all be explained by the exact same jet model, this is a powerful indicator that they all represent the same event. if true, that means that all short grbs weve observed were also caused by the violent collision of two neutron stars somewhere in the distant universe.citationgw170817 afterglow reveals that short gamma-ray bursts are neutron star mergers, yiyang wu and andrew macfadyen 2019 apjl 880 l23. doi:10.3847/2041-8213/ab2fd4 | uniting short gamma-ray bursts and neutron star mergers |
at 17:16:23 ut, the swift burst alert telescope (bat) triggered and located grb 220325a (trigger=1099310). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 269.485, -7.031 which is ra(j2000) = 17h 57m 56s dec(j2000) = -07d 01' 50" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about ~8 sec. the peak count rate was ~2000 counts/sec (15-350 kev), at ~1 sec after the trigger. the xrt began observing the field at 17:18:13.2 ut, 110.2 seconds after the bat trigger. using promptly downlinked data we find a fading, uncatalogued x-ray source located at ra, dec 269.48760, -7.03776 which is equivalent to: ra(j2000) = 17h 57m 57.02s dec(j2000) = -07d 02' 15.9" with an uncertainty of 3.9 arcseconds (radius, 90% containment). this location is 26 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. no spectrum from the promptly downlinked event data is yet available to determine the column density. uvot took a finding chart exposure of 150 seconds with the white filter starting 114 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.915. burst advocate for this burst is m. ferro (matteo.ferro at inaf.it). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 220325a: swift detection of a burst |
at 04:52:58 ut, the swift burst alert telescope (bat) triggered and located grb 220701a (trigger=1114034). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 242.478, +55.420 which is ra(j2000) = 16h 09m 55s dec(j2000) = +55d 25' 14" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a double-peaked structure with a duration of about 16 sec. the peak count rate was ~1000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 04:56:06.0 ut, 187.9 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 242.50589, 55.40679 which is equivalent to: ra(j2000) = 16h 10m 01.41s dec(j2000) = +55d 24' 24.4" with an uncertainty of 4.2 arcseconds (radius, 90% containment). this location is 74 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 1.03 x 10^20 cm^-2 (willingale et al. 2013). uvot took a finding chart exposure of 150 seconds with the white filter starting 175 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 85% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.008. burst advocate for this burst is p. a. evans (pae9 at leicester.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 220701a: swift detection of a burst |
at 11:11:17 ut, the swift burst alert telescope (bat) triggered and located grb 210205a (trigger=1030629). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 347.257, +56.312 which is ra(j2000) = 23h 09m 02s dec(j2000) = +56d 18' 45" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve shows a multi-peak structure with a duration of about 35 sec. the peak count rate was ~1000 counts/sec (15-350 kev), at ~2 sec after the trigger. the xrt began observing the field at 11:13:32.2 ut, 134.7 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 347.2214, 56.2943 which is equivalent to: ra(j2000) = 23h 08m 53.13s dec(j2000) = +56d 17' 39.4" with an uncertainty of 2.6 arcseconds (radius, 90% containment). this location is 95 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 5.15 x 10^21 cm^-2 (willingale et al. 2013). uvot took a finding chart exposure of 150 seconds with the white filter starting 138 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 47% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the large, but uncertain, extinction expected. burst advocate for this burst is s. dichiara (dichiara at umd.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210205a: swift detection of a burst |
at 21:39:44 ut, the swift burst alert telescope (bat) triggered and located grb 210209a (trigger=1031636). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 328.096, +43.559 which is ra(j2000) = 21h 52m 23s dec(j2000) = +43d 33' 31" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a double-peaked structure with a duration of about 110 sec. the peak count rate was ~1600 counts/sec (15-350 kev), at ~5 sec after the trigger. the xrt began observing the field at 21:41:41.0 ut, 116.5 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 328.12298, 43.55745 which is equivalent to: ra(j2000) = 21h 52m 29.52s dec(j2000) = +43d 33' 26.8" with an uncertainty of 3.5 arcseconds (radius, 90% containment). this location is 70 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. no spectrum from the promptly downlinked event data is yet available to determine the column density. the initial flux in the 2.5 s image was 3.98e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 126 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.285. burst advocate for this burst is s. laha (sib.laha at gmail.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210209a: swift detection of a burst |
at 11:42:54 ut, the swift burst alert telescope (bat) triggered and located grb 200713a (trigger=982201). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 76.962, -32.825, which is ra(j2000) = 05h 07m 51s dec(j2000) = -32d 49' 30" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). as is the usual for image triggers, the light curve does not show anything. the xrt began observing the field at 11:45:24.7 ut, 150.1 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source with an enhanced position: ra, dec 76.9492, -32.8144 which is equivalent to: ra(j2000) = 05h 07m 47.81s dec(j2000) = -32d 48' 51.7" with an uncertainty of 2.7 arcseconds (radius, 90% containment). this location is 54 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 1.99 x 10^20 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 1.27e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 159 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.02. burst advocate for this burst is a. y. lien (amy.y.lien at nasa.gov). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200713a: swift detection of a burst |
at 07:58:20 ut, the swift burst alert telescope (bat) triggered and located igr j16418-4532 (trigger=1073821). swift slewed immediately to the source. the bat on-board calculated location is ra, dec 250.455, -45.540 which is ra(j2000) = 16h 41m 49s dec(j2000) = -45d 32' 22" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve is an image trigger and as such does not show any peak. the xrt began observing the field at 08:00:28.1 ut, 128.0 seconds after the bat trigger. xrt found a bright x-ray source located at ra, dec 250.4669, -45.5421 which is equivalent to: ra(j2000) = 16h 41m 52.06s dec(j2000) = -45d 32' 31.6" with an uncertainty of 4.9 arcseconds (radius, 90% containment). this location is 30 arcseconds from the bat onboard position, within the bat error circle. this position is 15.1 arcseconds from a known x-ray source: 2sxps j164150.7-453225, also known as igrj16418-4532. this source is in the swift xrt 2sxps catalogue with a mean 0.3-10 kev count-rate of 0.2893 +/- 0.0028 ct/sec; see https://www.swift.ac.uk/2sxps/2sxps%20j164150.7-453225 for details of these previous observations. no event data are yet available to determine the column density using x-ray spectroscopy. uvot took a finding chart exposure of 250 seconds with the u filter starting 133 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.2 mag. the coverage of the xrt error circle by the 8'x8' region for the list of sources generated on-board is uncertain because the large number of sources filled the available telemetry. the list of sources is typically complete to about 18.0 mag. no correction has been made for the large, but uncertain, extinction expected. | swift trigger 1073821: detection of igr j16418-4532 |
at 16:41:56 ut, the swift burst alert telescope (bat) triggered and located grb 180623a (trigger=844015). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 214.511, -60.294, which is ra(j2000) = 14h 18m 03s dec(j2000) = -60d 17' 38" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve shows 4 large peaks and many little peaks with a total duration of about 90 sec. the peak count rate was ~6500 counts/sec (15-350 kev), at ~61 sec after the trigger. the xrt began observing the field at 16:43:13.3 ut, 76.9 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source with an enhanced position: ra, dec 214.5295, -60.2539 which is equivalent to: ra(j2000) = 14h 18m 07.08s dec(j2000) = -60d 15' 13.9" with an uncertainty of 2.1 arcseconds (radius, 90% containment). this location is 148 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. the initial flux in the 2.5 s image was 1.31e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of nominal 150.000 seconds with the white filter starting 85 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the list of sources is typically complete to about 18 mag. no correction has been made for the large, but uncertain, extinction expected. although this source is close to the galactic plane (lat = 0.83 degrees), its distance from the galactic center (46 degrees), the presence of significant flux above 100 kev, and the complexity and overall shape of the lightcurve are consistent with a grb that is aligned with the plane due to random coincidence. burst advocate for this burst is k. l. page (klp5 at leicester.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/too.html.) | grb 180623a: swift detection of a burst |
we observed the field of the short grb 230217a (moss et al. gcn circ. 33339) with the eso/vlt equipped with the fors2 instrument. a series of optical images has been obtained with the i filter on 2023 february 20 (i.e. about 2.5 days after the burst) and on 2023 february 23 (i.e. about 5.5 days after the burst). image subtraction carried out between the two epochs shows a residual at the following position: ra (j2000) = 18:43:04.97 dec (j2000) = -28:50:16.4 +/- 0.3". this position lies inside the xrt error circle of the x-ray afterglow position (capalbi et al., gcn circ. 33365) and is consistent with the position of the radio source reported by schroeder et al. (gcn circ. 33358). from preliminary photometry, we measure for this source a magnitude of i ~ 24.5 (ab) at t-t0 = 2.5 days. we propose this source as a candidate optical counterpart of grb 230217a. further observations are planned. we acknowledge excellent support from the eso observing staff in paranal, in particular julia seidel, konrad tristram and thomas rivinius. | grb 230217a: vlt/fors2 optical observations and candidate counterpart |
at 17:38:00 ut, the swift burst alert telescope (bat) triggered and located grb 210820a (trigger=1069551). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 20.629, +4.632 which is ra(j2000) = 01h 22m 31s dec(j2000) = +04d 37' 55" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 30 sec. the peak count rate was ~500 counts/sec (15-350 kev), at ~8 sec after the trigger. the xrt began observing the field at 17:40:05.7 ut, 125.0 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 20.6376, 4.6071 which is equivalent to: ra(j2000) = 01h 22m 33.02s dec(j2000) = +04d 36' 25.6" with an uncertainty of 11.1 arcseconds (radius, 90% containment). this location is 94 arcseconds from the bat onboard position, within the bat error circle. no event data are yet available to determine the column density using x-ray spectroscopy. the initial flux in the 2.5 s image was 3.75e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 250 seconds with the u filter starting 130 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 01:22:33.48 = 20.63952 dec(j2000) = +04:36:28.2 = 4.60783 with a 90%-confidence error radius of about 0.76 arc sec. this position is 7.4 arc sec. from the center of the xrt error circle. the estimated magnitude is 17.53 with a 1-sigma error of about 0.15. no correction has been made for the expected extinction corresponding to e(b-v) of 0.031. burst advocate for this burst is a. p. beardmore (apb at star.le.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210820a: swift detection of a burst with an optical counterpart |
swift-xrt has performed follow-up observations of the swift/bat-detected burst grb 220831a (tohuvavohu et al. gcn circ. 32506), collecting 5.0 ks of photon counting (pc) mode data between t0+51.2 ks and t0+78.8 ks. no x-ray sources have been detected consistent with being within 98 arcsec of the swift/bat position. the 3-sigma upper limit in the field ranges from ~0.002 to ~0.003 ct s^-1, corresponding to a 0.3-10 kev observed flux of 8.1e-14 to 1.1e-13 erg cm^-2 s^-1 (assuming a typical grb spectrum). we report, however, the presence of a low-significance source, at the following position: ra (j2000.0): 24.25359 = 01:37:00.86 dec (j2000.0): -41.59325 = -41:35:35.70 error: 6.8 arcsec (radius, 90% conf.) distance: 41 arcsec from swift-bat position. given the low-significance detection, we cannot state at the present stage if this detection is real or spurious. six uncatalogued sources were detected too far from the grb position to be likely afterglow candidates. the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/00021512. this circular is an official product of the swift-xrt team. | grb 220831a: swift-xrt observations |
at 21:08:03 ut, the swift burst alert telescope (bat) triggered and located grb 191101a (trigger=932742). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 251.844, +43.754 which is ra(j2000) = 16h 47m 23s dec(j2000) = +43d 45' 15" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 20 sec. the peak count rate was ~1200 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 21:09:42.4 ut, 99.0 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 251.83474, 43.74103 which is equivalent to: ra(j2000) = 16h 47m 20.34s dec(j2000) = +43d 44' 27.7" with an uncertainty of 4.0 arcseconds (radius, 90% containment). this location is 52 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. no spectrum from the promptly downlinked event data is yet available to determine the column density. the initial flux in the 2.5 s image was 8.42e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 109 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers none of the xrt error circle. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.01. burst advocate for this burst is a. d'ai (antonino.dai at inaf.it). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 191101a: swift detection of a burst |
we report the discovery of the fast optical transient ztf21aagwbjr/at2021buv with the zwicky transient facility (ztf, bellm et al. 2019, graham et al. 2019) at coordinates (j2000, <0.5"): ra = 07:48:19.32 (117.08054d) dec = +11:24:34.21 (+11.40949d) ztf21aagwbjr was first detected at r=17.11 mag on 2021-02-04 07:07 ut, hereafter labelled t_det, with an upper limit (g > 18.74 mag) 1.9 hours prior. it faded by ~2.1 mag in r-band in the next 0.9 days. the transient was most recently detected on 2021-02-05 06:07 ut at g = 19.70 ± 0.07 mag. the color appears to be red, with g-r~0.4 on 2021-02-05. the galactic extinction along the line of sight is low, with e(b-v)=0.04 mag (planck collaboration et al., 2015). we note that ztf21aagwbjr falls in the center of the error region of grb210204a (gcn 29390), a long burst triggered by fermi gbm 45 minutes before t_det. ztf21aagwbjr is temporally and spatially consistent with grb210204a (see https://zwicky.tf/j0s), and likely the afterglow. in the table below, we report photometry obtained on images processed in real-time through the ztf reduction and image subtraction pipelines at ipac (masci et al. 2019). ------------------------------------- date (ut) | mag | emag | band ------------------------------------- 2021-02-04 05:14 | > 18.74 | - | g 2021-02-04 07:07 | 17.11 | 0.02 | r 2021-02-05 05:09 | 19.26 | 0.06 | r 2021-02-05 06:07 | 19.70 | 0.07 | g ------------------------------------- ztf21aagwbjr is located off the galactic plane, with galactic latitude b_gal = 17.7 deg. a possible faint host is listed in the legacy survey dr9 catalog (dey et al. 2019, apj, 157, 5), at ra, dec = 07:48:19.32, 11:24:34.3, with a small separation of 0.1 arcsec from ztf21aagwbjr. the source has a galaxy morphological classification, according to the dr9 tractor model. the possible host has reported magnitudes of g=24.60, r=23.74, z=23.26, and a photometric redshift of 0.92 ± 0.3. we encourage spectroscopic classification and multi-wavelength follow-up of ztf21aagwbjr, the likely afterglow of grb210204a. ztf21aagwbjr was observed as part of the caltech tess shadowing survey (atel #12952), and identified independently by two ztf data mining programs: i) the "ztf realtime search and triggering" (ztf-rest) project, which aims at near real-time identification of compelling kilonova candidates in ztf data using the methods described in andreoni et al. (2020, apj, 904, 2), independently of gravitational-wave or gamma-ray triggers; ii) a filtering algorithm designed for fast transient discovery (ho et al. 2020, apj, 905, 2). ztf and growth are worldwide collaborations comprising caltech, usa; ipac, usa, wis, israel; okc, sweden; jsi/umd, usa; u washington, usa; desy, germany; most, taiwan; uw milwaukee, usa; lanl usa; tokyo tech, japan; iitb, india; iia, india; ljmu, uk; ttu, usa; sdsu, usa and usyd, australia. ztf acknowledges the generous support of the nsf under ast msip grant no 1440341. growth acknowledges generous support of the nsf under pire grant no 1545949. alert distribution service provided by dirac@uw (patterson et al. 2019). alert database searches are done with kowalski (duev et al. 2019). | ztf21aagwbjr/at2021buv: ztf discovery of a fast optical transient likely associated with grb 210104a |
at 08:11:21 ut, the swift burst alert telescope (bat) triggered and located the soft gamma repeater sgr 1830-0645 (trigger=1033144). swift slewed immediately to the source. the bat on-board calculated location is ra, dec 277.646, -6.735 which is ra(j2000) = 18h 30m 35s dec(j2000) = -06d 44' 05" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a single-peaked structure with a duration of about 0.1 sec. the peak count rate was ~10000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 08:12:33.2 ut, 71.9 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 277.67287, -6.75438 which is equivalent to: ra(j2000) = 18h 30m 41.49s dec(j2000) = -06d 45' 15.8" with an uncertainty of 4.2 arcseconds (radius, 90% containment). this location is 118 arcseconds from the bat onboard position, within the bat error circle, and consistent with the known location of sgr 1830-0645. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (1.11 x 10^22 cm^-2, willingale et al. 2013), with an excess column of 2.7 (+4.47/-2.40) x 10^22 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 76 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers none of the xrt error circle. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. no correction has been made for the large, but uncertain, extinction expected. bat most recently triggered on sgr 1830-0645 on 2021 feb 13 (gcn 29500). | swift trigger 1033144: detection of sgr 1830-0645 |
the circumgalactic medium (cgm) is the site of various galactic phenomena such as galactic winds, outflows, accretion flows, and recycling flows. recent space- and ground-based studies of the circumgalactic medium (cgm) using bright background quasars have revealed a dynamic interplay between the galaxy ecosystem and surrounding cgm. in this study, we extend this investigation of the cgm to higher redshifts (z > 2) by using the bright afterglows of gamma-ray bursts as background sources. thanks to their bright uv/optical/nir afterglows, promptly acquired spectroscopic data show exquisite absorption lines from both the cgm and interstellar medium (ism) of the grb host galaxy along the line of sight traced by the afterglow light. we compiled a sample of 27 high-resolution (r > 8000) and high signal-to-noise (typical s/n ~ 15) spectra of grb afterglows covering a redshift range of z ~ 2 to 6, with six of them at z > 4. the column densities (n), doppler parameters (b) and line-centroids of both high-ionization (o vi, c iv, si iv, n v) and low-ionization species (si ii, c ii*, fe ii, etc) are extracted to study the kinematics of different phases in the cgm. we observed an excess absorption in the blue wings of high-ion absorption features, unlike the typical symmetrical distribution of the low-ion absorption features. in addition, the column density ratios of high- to low-ion lines clearly show the existence of three absorption regimes: a) blueward of -100 km/s, b) within +/-100 km/s and c) redward of 100 km/s. we hypothesize that these populations are: a) predominantly warm cgm outflows at high velocity, b) a combination of cgm at low-velocity and galaxy ism, and c) cool cgm inflows, respectively. we use a toy-model to corroborate the outflow signatures in grb afterglow spectra and estimate the cgm mass, assuming a typical grb host galaxy. through this study, we establish that grb afterglows are crucial probes of cgm evolution at high redshifts. | cgm-grb: studying the circumgalactic medium around grb hosts at z > 2 |
swift-xrt has performed follow-up observations of the swift/bat-detected burst grb 211107b (swift/bat did not successfully trigger on grb 211107b et al. gcn circ. 31057), collecting 1.7 ks of photon counting (pc) mode data between t0+124.3 ks and t0+131.0 ks. one uncatalogued x-ray source has been detected consistent with being within 197 arcsec of the swift/bat position, it is below the rass limit and shows no definitive signs of fading. therefore, at the present time we cannot confirm this as the afterglow. details of this source are given below: source 1: ra (j2000.0): 65.80807 = 04:23:13.94 dec (j2000.0): -27.56097 = -27:33:39.5 error: 2.9 arcsec (radius, 90% conf. [enhanced position]) count-rate: 0.0220 +/- 0.0042 ct s^-1 distance: 52 arcsec from swift/bat position. flux: (5.15 +/- 0.98)e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/00021467. this circular is an official product of the swift-xrt team. | grb 211107b: swift-xrt observations |
at 16:18:51 ut, the swift burst alert telescope (bat) triggered and located grb 220117a (trigger=1093592). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 91.578, -28.410 which is ra(j2000) = 06h 06m 19s dec(j2000) = -28d 24' 35" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 65 sec. the peak count rate was ~900 counts/sec (15-350 kev), at ~15 sec after the trigger. the xrt began observing the field at 16:21:23.4 ut, 151.9 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 91.57277, -28.43760 which is equivalent to: ra(j2000) = 06h 06m 17.46s dec(j2000) = -28d 26' 15.4" with an uncertainty of 3.7 arcseconds (radius, 90% containment). this location is 100 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 2.57 x 10^20 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 6.01e-10 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 161 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.029. burst advocate for this burst is a. melandri (andrea.melandri at brera.inaf.it). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 220117a: swift detection of a burst |
we present a numerical model for calculation of spectra of synchrotron-self-compton radiation sources, e.g., gamma-ray bursts and tev blazars. the model implements sequential allowance of the compton scattering and two-photon production of electron-positron pairs using precise quantum-electrodynamic expressions for the corresponding differential equations. the previously unknown phenomena revealed by using the model are discussed, and an example of modeling the actual spectrum observed in the afterglow of the grb 190114c gamma-ray burst is presented. | numerical model of synchrotron-self-compton radiation sources |
swift-xrt has performed follow-up observations of the swift/bat-guano detected burst grb 210606a (james delaunay et al. gcn circ. 30134), collecting 7.3 ks of photon counting (pc) mode data between t0+62.3 ks and t0+385.7 ks. four uncatalogued x-ray sources are detected consistent with being within 394 arcsec of the swift/bat position, of which one ("source 1") is fading with 4.6-sigma significance, and is therefore likely the grb afterglow. using 4521 s of pc mode data and 5 uvot images, we find an enhanced xrt position (using the xrt-uvot alignment and matching uvot field sources to the usno-b1 catalogue): ra, dec = 170.94110, +0.81293 which is equivalent to: ra (j2000): 11h 23m 45.86s dec(j2000): +00d 48' 46.5" with an uncertainty of 2.3 arcsec (radius, 90% confidence). this position is 6.1 arcmin from the swift/bat position. the light curve can be modelled with a power-law decay with a decay index of alpha=1.1 (+0.9, -0.6). a spectrum formed from the pc mode data can be fitted with an absorbed power-law with a photon spectral index of 1.8 (+0.5, -0.4). the best-fitting absorption column is 1.4 (+1.6, -1.0) x 10^21 cm^-2, consistent with the galactic value of 3.8 x 10^20 cm^-2 (willingale et al. 2013). the counts to observed (unabsorbed) 0.3-10 kev flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. a summary of the pc-mode spectrum is thus: total column: 1.4 (+1.6, -1.0) x 10^21 cm^-2 galactic foreground: 3.8 x 10^20 cm^-2 excess significance: <1.6 sigma photon index: 1.8 (+0.5, -0.4) the results of the xrt-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/too_grbs/00021451/source1.php. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021451. this circular is an official product of the swift-xrt team. | grb 210606a: swift-xrt afterglow detection |
at 17:40:33 ut, the swift burst alert telescope (bat) triggered and located grb 220319a (trigger=1098132). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 218.207, +61.289 which is ra(j2000) = 14h 32m 50s dec(j2000) = +61d 17' 20" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a single-peaked structure with a duration of about 10 sec. the peak count rate was ~1400 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 17:42:14.5 ut, 101.2 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 218.22471, 61.29389 which is equivalent to: ra(j2000) = 14h 32m 53.93s dec(j2000) = +61d 17' 38.0" with an uncertainty of 3.7 arcseconds (radius, 90% containment). this location is 35 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. no spectrum from the promptly downlinked event data is yet available to determine the column density. uvot took a finding chart exposure of 250 seconds with the u filter starting 317 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.2 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18.0 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.010. burst advocate for this burst is k. l. page (kimlpage1978 at gmail.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 220319a: swift detection of a burst |
at 21:16:47 ut, the swift burst alert telescope (bat) triggered and located a new sgr (trigger=960986). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 274.471, -16.102 which is ra(j2000) = 18h 17m 53s dec(j2000) = -16d 06' 05" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a single-peak structure with a duration of about 0.1 sec. the peak count rate was ~1500 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 21:17:51.2 ut, 64.2 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 274.5009, -16.1312 which is equivalent to: ra(j2000) = 18h 18m 00.22s dec(j2000) = -16d 07' 52.3" with an uncertainty of 2.4 arcseconds (radius, 90% containment). this location is 147 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. uvot took a finding chart exposure of 150 seconds with the white filter starting 68 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers none of the xrt error circle. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the large, but uncertain, extinction expected. the extremely short and relatively soft nature of the bat detection, combined with the source's closeness to the galactic plane (b=-0.14 deg), is suggestive that this trigger is from a previously undiscovered sgr. if this is a new sgr and not a grb, we name the source swift j1818.0-1607. burst advocate for this burst is p. a. evans (pae9 at star.le.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | swift-bat trigger 960986: swift detection of a new sgr swift j1818.0-1607 |
at 15:50:37 ut, the swift burst alert telescope (bat) triggered and located grb 180620b (trigger=843211). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 357.517, -57.957 which is ra(j2000) = 23h 50m 04s dec(j2000) = -57d 57' 25" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 30 sec. the peak count rate was ~9000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 15:52:00.3 ut, 83.2 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 357.52114, -57.96306 which is equivalent to: ra(j2000) = 23h 50m 05.07s dec(j2000) = -57d 57' 47.0" with an uncertainty of 3.7 arcseconds (radius, 90% containment). this location is 23 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 1.39 x 10^20 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 7.04e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 91 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 23:50:05.10 = 357.52126 dec(j2000) = -57:57:44.1 = -57.96224 with a 90%-confidence error radius of about 0.75 arc sec. this position is 1.7 arc sec. from the center of the xrt error circle. the estimated magnitude is 17.98 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.01. burst advocate for this burst is p. a. evans (pae9 at star.le.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/too.html.) | grb 180620b: swift detection of a burst with an optical counterpart |
the rapid infrared imager/spectrograph (rimas) is an instrument designed to observe gamma ray burst afterglows in the near infrared between 0.9 and 2.4 μm. dispersion in the moderate resolution mode (r~4000) is provided by a pair of znse grisms: one covering the y and j bands and the other covering the h and k. llnl diamond machined the original pair of grisms several years ago, which are currently installed in the rimas instrument. we were tasked to fabricate a second pair of grisms and incorporated several improvements developed during the fabrication of the first set. the second hk grism showed some chipping near the end of the cut, but overall was much higher quality than the first hk grism. the rms surface error was reduced by a factor of 3 over the first hk to 0.085l at 633 nm and the wavefront error in the transmitted beam is well below the diffraction limit in the h and k bands. we measured a diffraction efficiency of 47% at 633 nm. the second yj grism is currently being machined. | a second set of znse grisms for the rapid infrared imager/spectrograph (rimas) |
the rapid imager - spectrometer (rimas) will study the afterglow of gamma-ray bursts in the near-infrared. in order to produce useful astronomical data, rimas must be calibrated to establish what wavelength corresponds to each pixel on the spectrometer's h2rg detectors. in the first phase of this study, several methods of determining the pixel number of spectral peaks were developed in python and compared to find which produced the most accurate calibration curve. three different approaches were attempted using test spectra taken by rimas of elements with known emission lines: finding the pixel number of peaks in a one-dimensional line spectrum, fitting two-dimensional gaussians over the peaks and finding the pixel number of their maxima, and finding the centers of mass of the peaks at a certain intensity threshold, which was then varied. once the pixel numbers of peaks were found, a linear regression with the known wavelengths of the spectral lines was performed to produce a calibration curve. after a comparison of the r2 value and the maximum percent difference between library and calibrated wavelengths produced by the different methods, the best calibration curve was shown to be produced by finding center of mass with an intensity threshold of 35%. the next phase of this project is to establish the spectral extraction pathway for rimas using spextool. this requires the construction of line and wavelength calibration files specific to rimas, which will be incorporated into the existing spextool pathway. using this package, observers will have a pipeline to create calibration files and extract the spectrum of their target object. the extraction of data from rimas that this enables will be integral to researching distant gamma-ray bursts. | exploration of the calibration and development of the spectral extraction procedure for the rapid imager - spectrometer |
at 15:04:36 ut, the swift burst alert telescope (bat) triggered and located grb 210901a (trigger=1071488). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 295.292, -76.932 which is ra(j2000) = 19h 41m 10s dec(j2000) = -76d 55' 55" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 60 sec. as this is an image trigger a more complete description of the lightcurve will require the ground pass data. the peak count rate was ~500 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 15:07:07.7 ut, 151.4 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source with an enhanced position: ra, dec 295.2774, -76.9263 which is equivalent to: ra(j2000) = 19h 41m 06.57s dec(j2000) = -76d 55' 34.8" with an uncertainty of 1.9 arcseconds (radius, 90% containment). this location is 23 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 1.02 x 10^21 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 1.86e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 157 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.200. burst advocate for this burst is s. laha (sib.laha at gmail.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210901a: swift detection of a burst |
at 21:29:28 ut, the swift burst alert telescope (bat) triggered and located grb 221120a (trigger=1141030). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 41.3225 43.1970 which is ra(j2000) = 02h 45m 17s dec(j2000) = 43d 11' 49" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat trigger duration was 0.256 s, suggesting a possible short burst. due to a telemetry gap, no further bat information will be available until ground contact. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 41.33852, 43.24280 which is equivalent to: ra(j2000) = 02h 45m 21.24s dec(j2000) = +43d 14' 34.1" with an uncertainty of 1.9 arcseconds (radius, 90% containment). this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. uvot took a finding chart exposure of 150 seconds with the white filter. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 0% of the xrt error circle. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. burst advocate for this burst is r. a. j. eyles-ferris (raje1 at leicester.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 221120a: swift detection of a likely short burst |
at 15:36:18 ut, the swift burst alert telescope (bat) triggered and located grb 180613a (trigger=840853). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 211.562, -43.076 which is ra(j2000) = 14h 06m 15s dec(j2000) = -43d 04' 31" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). as is usual with an image trigger, the available bat light curve shows no significant structure. the xrt began observing the field at 15:38:47.7 ut, 148.9 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source located at ra, dec 211.52004, -43.07158 which is equivalent to: ra(j2000) = 14h 06m 04.81s dec(j2000) = -43d 04' 17.7" with an uncertainty of 3.7 arcseconds (radius, 90% containment). this location is 111 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (6.50 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 4.5 (+3.67/-3.01) x 10^21 cm^-2 (90% confidence). the initial flux in the 2.5 s image was 5.63e-10 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 250 seconds with the u filter starting 154 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.2 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18.0 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.09. burst advocate for this burst is a. tohuvavohu (aaronb at swift.psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/too.html.) | grb 180613a: swift detection of a burst |
we perform two dimensional mhd cellular automata simulations for a two-dimensional model of a magnetized flux tube with a background flow. self organized criticality is reached by the system. the lifetime distribution and energy emission as a function of time are discussed regarding an application of the model to x-ray emission of gamma ray bursts. | mhd cellular automata simulations: application to grb x-ray afterglows |
swift-xrt has performed follow-up observations of the fermi/gbm and swift/bat-guano detected burst grb 201008a (delaunay et al. gcn circ. 28583), collecting 4.5 ks of photon counting (pc) mode data between t0+46.9 ks and t0+60.1 ks. two uncatalogued x-ray sources have been detected consistent with being within 296 arcsec of the bat/guano position, however none of them is above the rass limit or shows definitive signs of fading. therefore, at the present time we cannot identify which, if any, is the afterglow. details of these sources are given below: source 1: ra (j2000.0): 161.7543 = 10:47:1.02 dec (j2000.0): +46.1475 = +46:08:51.1 error: 5.1 arcsec (radius, 90% conf.) count-rate: (1.79 [+1.09, -0.80])e-3 ct s^-1 distance: 169 arcsec from bat position. nb, this position is consistent with sdss j104701.20+460848.8, a likely quasar in the sdss quasar catalogue. if this association and id is accurate, this source is unlikely to be related to the grb. source 4: ra (j2000.0): 161.8588 = 10:47:26.10 dec (j2000.0): +46.1019 = +46:06:06.9 error: 4.8 arcsec (radius, 90% conf.) count-rate: (4.1 [+1.3, -1.1])e-3 ct s^-1 distance: 286 arcsec from bat position. flux: (1.68 [+0.52, -0.44])e-10 erg cm^-2 s^-1 (observed, 0.3-10 kev) two uncatalogued sources were also detected too far from the grb position to be likely afterglow candidates. the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/00021034. this circular is an official product of the swift-xrt team. | grb 201008a: swift-xrt observations |
we present the discovery of a slowly-evolving, extragalactic radio transient, first j141918.9+394036, identified by comparing a catalog of radio sources in nearby galaxies against new observations from the very large array sky survey. analysis of other archival data shows that first j141918.9+394036 faded by a factor of ∼50 over 23 years, from a flux of ∼26 mjy at 1.4 ghz in 1993 to an upper limit of 0.4 mjy at 3 ghz in 2017. first j141918.9+394036 is likely associated with the small star-forming galaxy sdss j141918.81+394035.8 at a redshift z=0.01957 (d=87 mpc), which implies a peak luminosity νlν ≧ 3×10^38 erg/s. if interpreted as an isotropic synchrotron blast wave, the source requires an explosion of kinetic energy ∼10^51 erg some time prior to our first detection in late 1993. this explosion is most likely associated with a long gamma-ray burst (grb), but the radio source could also be interpreted as the nebula of a newly-born magnetar. the radio discovery of either of these phenomena would be unprecedented. joint consideration of the event light curve, host galaxy, lack of a counterpart gamma-ray burst, and volumetric rate suggests that first j141918.9+394036 is the afterglow of an off-axis (``orphan'') long grb. the long time baseline of this event offers the best available constraint in afterglow evolution as the bulk of shock-accelerated electrons become non-relativistic. the proximity, age, and precise localization of first j141918.9+394036 make it a key object for understanding the aftermath of rare classes of stellar explosion. | discovery of the luminous, decades-long, extragalactic radio transient first j141918.9+394036 |
at 15:03:43 ut, the swift burst alert telescope (bat) triggered and located grb 210610a (trigger=1054627). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 204.285, +14.480 which is ra(j2000) = 13h 37m 08s dec(j2000) = +14d 28' 49" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 15 sec. the peak count rate was ~2000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 15:05:13.3 ut, 90.0 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 204.2823, 14.4652 which is equivalent to: ra(j2000) = 13h 37m 07.76s dec(j2000) = +14d 27' 54.7" with an uncertainty of 2.2 arcseconds (radius, 90% containment). this location is 54 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. no spectrum from the promptly downlinked event data is yet available to determine the column density. uvot took a finding chart exposure of 150 seconds with the white filter starting 93 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 13:37:07.62 = 204.28174 dec(j2000) = +14:27:55.0 = 14.46528 with a 90%-confidence error radius of about 0.61 arc sec. this position is 2.2 arc sec. from the center of the xrt error circle. the estimated magnitude is 17.12 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.032. burst advocate for this burst is k. l. page (klp5 at leicester.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210610a: swift detection of a burst with an optical counterpart |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 220627a (di lalla et al. gcn circ. 32283), collecting 4.9 ks of photon counting (pc) mode data between t0+44.3 ks and t0+148.8 ks. fourteen uncatalogued x-ray sources are detected, of which one ("source 3") is fading with >3-sigma significance, and is therefore likely the grb afterglow. using 1679 s of pc mode data and 1 uvot image, we find an enhanced xrt position (using the xrt-uvot alignment and matching uvot field sources to the usno-b1 catalogue): ra, dec = 201.36878, -32.42624 which is equivalent to: ra (j2000): 13h 25m 28.51s dec(j2000): -32d 25' 34.5" with an uncertainty of 3.1 arcsec (radius, 90% confidence). this position is 9.6 arcmin from the fermi/lat position and is consistent with the previously detected candidate afterglow (gcn circ 32289). the light curve can be modelled with a power-law decay with a decay index of alpha=1.4 (+0.8, -0.5). the results of the xrt-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021506. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021506. this circular is an official product of the swift-xrt team. | grb 220627a: swift-xrt afterglow detection |
at2023lcr is a recently discovered fast-fading red transient with multi-wavelength observations consistent with a typical long gamma-ray burst (grb) afterglow at redshift 1.0272. however, no gamma-ray prompt emission was detected in the direction of the transient. goto observations constrained the window of possible prompt emission allowing gamma-ray missions to set tight limits on the gamma-ray emission. based on these observations, there are two leading possible scenarios: an on-axis dirty fireball that had its prompt emission choked or an off-axis grb with a narrow jet whose prompt emission we missed. in the case of the dirty fireball, low lorentz factor implied by the lack of grb prompt emission also suggest a weaker jet collimation. here we propose to observe the x-ray afterglow of this rare case of grb to constrain its jet opening angle and distinguish between these two models and measure its true energetics. | determining the jet collimation of the dirty fireball grb candidate at2023lcr |
swift-xrt has performed follow-up observations of the swift/bat-guano-detected burst grb 210626a (aaron tohuvavohu et al. gcn circ. 30325), collecting 1.4 ks of photon counting (pc) mode data between t0+29.7 ks and t0+31.1 ks. an uncatalogued x-ray source is detected and is above the 2sxps 3-sigma upper limit at this position, and is therefore likely the grb afterglow. using 1180 s of pc mode data and 1 uvot image, we find an enhanced xrt position (using the xrt-uvot alignment and matching uvot field sources to the usno-b1 catalogue): ra, dec = 221.52429, -1.15625 which is equivalent to: ra (j2000): 14h 46m 05.83s dec(j2000): -01d 09' 22.5" with an uncertainty of 5.7 arcsec (radius, 90% confidence). this position is 5.7 arcmin from the swift/bat-guano position. we cannot determine at the present time whether the source is fading. the results of the xrt-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/too_grbs/00021453/source1.php. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021453. this circular is an official product of the swift-xrt team. | grb 210626a: swift-xrt afterglow detection |
swift-xrt has performed follow-up observations of ztf21aagwbjr (kool et al., 29405), which may be related to the fermi/gbm / gecam / ipn detected burst grb 210204a (gcn circ., 29390, gcn circ. 29392, gcn circ. 29408), collecting 2.9 ks of photon counting (pc) mode data between t0+160.9 ks and t0+173.2 ks. an uncatalogued x-ray source is detected consistent with being within 1 arcsec of the ztf position and is believed to be the afterglow, or at least, the x-ray counterpart of the ztf21aagwbjr. using 2886 s of pc mode data and 6 uvot images, we find an enhanced xrt position (using the xrt-uvot alignment and matching uvot field sources to the usno-b1 catalogue): ra, dec = 117.08071, +11.40951 which is equivalent to: ra (j2000): 07h 48m 19.37s dec(j2000): +11d 24' 34.2" with an uncertainty of 1.7 arcsec (radius, 90% confidence). this position is 0.7 arcsec from the ztf position. the light curve is consistent with a constant source of mean count rate 9.1e-02 ct/sec. a spectrum formed from the pc mode data can be fitted with an absorbed power-law with a photon spectral index of 1.73 (+0.31, -0.29). the best-fitting absorption column is 1.7 (+1.3, -1.1) x 10^21 cm^-2, in excess of the galactic value of 3.5 x 10^20 cm^-2 (willingale et al. 2013). the counts to observed (unabsorbed) 0.3-10 kev flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1. a summary of the pc-mode spectrum is thus: total column: 1.7 (+1.3, -1.1) x 10^21 cm^-2 galactic foreground: 3.5 x 10^20 cm^-2 excess significance: 2.0 sigma photon index: 1.73 (+0.31, -0.29) the results of the xrt-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00014055. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00014055. this circular is an official product of the swift-xrt team. | grb 210204a / ztf21aagwbjr: swift-xrt observations |
we have analysed 5.2 ks of photon counting (pc) mode xrt data for the swift-bat-detected burst grb 210618a (bernardini et al. gcn circ. 30250), collected between t0+65 s and t0+22.6 ks. three uncatalogued x-ray sources have been detected consistent with being within 296 arcsec of the swift-bat position, however none of them is above the rass limit or shows definitive signs of fading. two sources (source 1 and source 4) are consistent within the xrt error circle with two spectroscopically identified quasars, and the third one (source 2) is consistent with a sdss galaxy with photo_z=0.59 and marginally consistent with a candidate quasar. therefore, for the moment the most plausible afterglow candidate is source 2. swift will perform follow-up observations to confirm this candidate. details of these sources are given below: source 1: ra (j2000.0): 235.8870 = 15:43:32.87 dec (j2000.0): +46.0253 = +46:01:31.0 error: 8.9 arcsec (radius, 90% conf.) count-rate: (3.82 [+1.19, -1.00])e-3 ct s^-1 distance: 179 arcsec from swift-bat position. flux: (1.17 [+0.36, -0.30])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) this source is consistent with sdss j154332.15+460133.2, spectroscopically classified as a quasar at z = 0.657. source 2: ra (j2000.0): 235.7698 = 15:43:4.75 dec (j2000.0): +46.0691 = +46:04:08.6 error: 9.3 arcsec (radius, 90% conf.) count-rate: (4.0 +/- 1.0)e-3 ct s^-1 distance: 156 arcsec from swift-bat position. flux: (1.35 +/- 0.35)e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) this source is positionally consistent with sdss j154305.56+460405.0, a galaxy with photo_z = 0.590 +/- 0.153 and 12.2 arcsec away from sdss j154305.40+460418.7, a candidate quasar (richards et al., 2015, apjs, 219, 39). source 4: ra (j2000.0): 235.7183 = 15:42:52.39 dec (j2000.0): +46.0336 = +46:02:01.0 error: 8.7 arcsec (radius, 90% conf.) count-rate: (1.48 [+0.78, -0.60])e-3 ct s^-1 distance: 256 arcsec from swift-bat position. flux: (7.2 [+3.8, -2.9])e-14 erg cm^-2 s^-1 (observed, 0.3-10 kev) this source is positionally consistent with sdss j154251.96+460206.1, spectroscopically classified as a quasar at z = 2.130. six uncatalogued sources were also detected too far from the grb position to be likely afterglow candidates. the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/01056426. this circular is an official product of the swift-xrt team. | grb 210618a: swift-xrt observations |
at 20:54:42 ut, the swift burst alert telescope (bat) triggered and located grb 210722a (trigger=1061223). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 27.023, -6.354 which is ra(j2000) = 01h 48m 06s dec(j2000) = -06d 21' 14" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 30 sec. the peak count rate was ~1500 counts/sec (15-350 kev), at ~0 sec after the trigger. using promptly downlinked xrt data we find an uncatalogued x-ray source located at ra, dec 27.028, -6.345 which is equivalent to: ra(j2000) = +01h 48m 06.84 dec(j2000) = -06d 20' 42.7" with an uncertainty of 5.0 arcseconds (radius, 90% containment). uvot took a finding chart exposure of 150 seconds with the white filter starting 94 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 01:48:07.27 = 27.03028 dec(j2000) = -06:20:49.8 = -6.34718 with a 90%-confidence error radius of about 0.74 arc sec. this position is 9.6 arc sec. from the center of the xrt error circle. the estimated magnitude is 14.37 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.027. burst advocate for this burst is p. d'avanzo (paolo.davanzo at inaf.it). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210722a: swift detection of a burst with a bright optical counterpart |
at 04:25:18 ut, the swift burst alert telescope (bat) triggered and located grb 210212a (trigger=1032183). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 72.261, +7.234 which is ra(j2000) = 04h 49m 03s dec(j2000) = +07d 14' 01" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a structure with a duration of about 50 sec. the peak count rate was ~1200 counts/sec (15-350 kev), at ~6 sec after the trigger. the xrt began observing the field at 04:27:00.9 ut, 103.0 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source with an enhanced position: ra, dec 72.2666, 7.2693 which is equivalent to: ra(j2000) = 04h 49m 03.99s dec(j2000) = +07d 16' 09.5" with an uncertainty of 3.8 arcseconds (radius, 90% containment). this location is 128 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. no spectrum from the promptly downlinked event data is yet available to determine the column density. the initial flux in the 2.5 s image was 9.74e-10 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 250 seconds with the u filter starting 270 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.2 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18.0 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.094. burst advocate for this burst is e. troja (eleonora.troja at nasa.gov). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210212a: swift detection of a burst |
at 04:57:29 ut, the swift burst alert telescope (bat) triggered and located grb 210730a (trigger=1062150). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 149.592, +69.705 which is ra(j2000) = 09h 58m 22s dec(j2000) = +69d 42' 19" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). although the bat lightcurve is not immediately available due to telemetry limitations, the trigger information indicates a very bright peak (68 sigma in rates) of at least 1 second duration. the xrt began observing the field at 04:58:50.8 ut, 81.6 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 149.59149, 69.69227 which is equivalent to: ra(j2000) = 09h 58m 21.96s dec(j2000) = +69d 41' 32.2" with an uncertainty of 8.2 arcseconds (radius, 90% containment). this location is 45 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. no spectrum from the promptly downlinked event data is yet available to determine the column density. the initial flux in the 2.5 s image was 6.73e-10 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 113 seconds with the white filter starting 90 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image processing failed because of no aspect solution. data from the list of sources generated on-board are not available at this time. no correction has been made for the expected extinction corresponding to e(b-v) of 0.096. we note that this location is close to the nearby galaxy m82, although well outside the main disk. for this reason, the initial gcn notice misreported it as a galactic transient. burst advocate for this burst is e. sonbas (edasonbas at yahoo.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210730a: swift detection of a burst near m82 |
in august 2017 a gravitational wave signal from a binary neutron star merger was detected for the first time, and it was followed by several electromagnetic detections that spanned the whole electromagnetic spectrum. those observations proved the ejection of two dynamical components: mildly-relativistic neutron rich ejecta and an ultra-relativistic jet. the first one produced a rapidly evolving thermal transient powered by the radioactive decay of the freshly synthesized r- process nuclei and subsequent recombination, named "macronova" or "kilonova". the second component powered instead a gamma-ray burst consisting of an early (and anomalous) gamma-ray signal ≍1.7 second after the merger followed by a long lasting multi-wavelength afterglow. these two dynamical components are typically observed and modelled independently, but when a jet is produced and propagates through the surrounding environment the properties of both may change significantly because of the interaction. however the observational consequences of such interaction are still unclear. in this thesis i present a comprehensive introduction to the properties of jets and post-merger ejecta, with the aim to show how 3d hydrodynamic simulations form a key instrument in investigating their interaction. i present the results of some of the first simulations of jets propagating within a realistic post-merger wind, and how the properties of the macronova are significantly affected. as an example, this work shows how a jet can "punch-away" a fraction of high-opacity material at early times, causing the macronova becoming brighter and bluer for on-axis observers in the first few days following the merger. moreover such interaction represents the main contribution to the final shape of the jet, that has a crucial impact in the late time emission for off-axis observers. while looking forward for future detections, this thesis aims to show how crucial is a detailed understanding of the environment surrounding the merger and how, in case of a joint observation of a macronova and a jet, should be taken into account how the interaction might have an impact on the inferred properties of the system. | jet-ejecta interactions in neutron star mergers |
grb 161219b was discovered by the swift burst alert telescope (bat) on 2016 december 19 at 18:48:39 ut. the burst duration is t90=6.94+/-0.79s. the optical afterglow was discovered by the swift uv/optical telescope (uvot) in observations beginning 112s after the bat trigger (marshall & d'ai 2016gcn.20306....1m). spectroscopic observations 36h after the burst with the x-shooter instrument on the european southern observatory (eso) 8.2m very large telescope (vlt) provided a redshift of z=0.1475 (2016gcn.20321....1t). the swift x-ray telescope (xrt) began observing grb 161219b 108s after the bat trigger. the x-ray afterglow was localized to raj2000=06:06:51.37, dej2000=-26:47:29.7, with an uncertainty radius of 1.4" (90% containment). xrt continued observing the afterglow for 123 days in photon counting mode. we began observing grb 161219b with two 1m telescopes in sutherland (south africa), which are operated by the las cumbres observatory global network (lcogt), on 2016 december 19, 20:43 ut, at 1.9h since the grb, in sloan digital sky survey (sdss) r' and i' filters. observations with 1 and 2m lcogt telescopes (formerly faulkes telescopes north and south) both in hawaii and in siding springs (australia) proceeded on a daily basis for 4 days, followed by a regularly increasing spacing until 2017 january 14 (25 days post-grb). additional optical observations with the 2m liverpool telescope (lt) in the same filters culminated on january 23 (35 days post-grb). we obtained ubvgri imaging of grb 161219b from 2016 december 22 to 2017 march 21 using the direct ccd camera on the swope 1.0m telescope at las campanas observatory in chile. we observed grb 161219b with the low resolution imaging spectrometer on the 10m keck i telescope on 2017 march 29 in ubgriz bands. we obtained seven epochs of near-ir observations in the jhk bands with the wide-field camera (wfcam) mounted on the united kingdom infrared telescope (ukirt) spanning ~2.5 to ~270d. we present the results of our optical and near-ir (nir) photometry, together with a compilation of all other optical observations reported in gcn circulars in table 3. we obtained alma observations of the afterglow at 1.3 days after the burst through program 2016.1.00819.t (pi: laskar) in band 3, with two 4ghz-wide basebands centered at 91.5 and 103.5ghz, respectively. we observed the afterglow using the karl g. jansky very large array (vla) starting 0.5 days after the burst through program 15a-235 (pi: berger). we detected and tracked the flux density of the afterglow from 1.2 to 37ghz over nine epochs until ~159d after the burst. (4 data files). | vizier online data catalog: multiwavelength obs. of grb 161219b (laskar+, 2018) |
grb190829a is a rare nearby (z=0.08) gamma-ray burst of long duration, followed by a bright type ic supernova. recently it was proposed that events like grb190829a could produce large amounts of heavy metals, and be the dominant sources of galactic r-process enrichment . the characteristic signature would be a long-lived infrared emission, outshining the supernova light months after the explosion. the main obstacle in identifying this novel emission component is the bright grb afterglow. continued x-ray monitoring of this grb would characterize its non-thermal emission, and allow us to disentangle the afterglow contribution from any possible red excess. only chandra can resolve the grb counterpart from nearby contaminating sources. | unpicking the threads of a rare collapsar explosion |
the likely detection of gravitational waves associated with the inspiral of neutron star binaries by the upcoming advanced ligo/virgo observatories will be complemented by searches for electromagnetic counterparts over large areas of the sky by swift and other observatories. as short gamma-ray bursts (grb) are the most likely electromagnetic counterpart candidates to these sources, we can make predictions based upon the last decade of grb observations by swift and fermi. swift is uniquely capable of accurately localizing new transients rapidly over large areas of the sky in single and tiled pointings, enabling ground-based follow-up. we describe simulations of the detectability of short grb afterglows by swift given existing and hypothetical tiling schemes with realistic observing conditions and delays, which guide the optimal observing strategy and improvements provided by coincident detection with observatories such as fermi-gbm. | predictions for swift follow-up observations of advanced ligo/virgo gravitational wave sources |
the svom mission (space-based variable objects monitor) is a chinese-french satellite mission under development, devoted to collecting a complete sample of gamma-ray bursts (grbs) observed at multi-wavelengths with a high fraction of redshift determinations. in january 2017 the mission entered phase c, starting officially construction, and the launch is foreseen in 2021. the svom satellite is equipped with 4 instruments, 2 of which cover the prompt grb phase. the eclairs coded-mask imager surveys a 2-sr large portion of the sky in the 4-150 kev energy range, well suited for the detection of x-ray rich and highly redshifted grbs. the eclairs trigger system continuously searches for grbs using two algorithms, a count-rate trigger for short time scales and an image trigger for long time scales. in case of a localized new grb candidate or a bright outburst of a known source, it promptly requests a satellite slew and sends an alert to ground. the onboard grm (gamma-ray monitor) extends the prompt energy coverage up to 5 mev. after slew, 2 more onboard instruments study the grb afterglow and refine the grb localization: the mxt (multi-pore optics x-ray telescope) and the vt (visible telescope). two types of ground telescopes are dedicated to svom. the gfts (ground follow-up telescopes) repoint autonomously to grb alerts, refine their localization and provide photometric redshift. the svom observing strategy with roughly antisolar pointing combined with galactic plane avoidance, ensures that most grbs are quickly visible by the gfts and large spectroscopic telescopes. the gwac (ground wide angle camera) will observe the sky simultaneously with eclairs to detect prompt optical grb emissions. today part of the gwac is already operational. the svom grb program is complemented by pre-planned target observations and ground-commanded targets of opportunity, e.g. to search for electromagnetic counterparts of gravity-wave events. on behalf of the svom and eclairs teams, this paper presents an overview of svom with a focus on its grb trigger system. | overview of the svom gamma-ray burst mission under development with a focus on its trigger system |
we show that the weibel or current filamentation instability can lead to the emission of circularly polarized radiation. using particle-in-cell simulations and a radiation post-processing numerical algorithm, we demonstrate that the level of circular polarization increases with the initial plasma magnetization, saturating at ${∼ }13 %$ when the magnetization, given by the ratio of magnetic energy density to the electron kinetic energy density, is larger than 0.05. furthermore, we show that this effect requires an ion-electron mass ratio greater than unity. these findings, which could also be tested in currently available laboratory conditions, show that the recent observation of circular polarization in gamma-ray burst afterglows could be attributed to the presence of magnetized current filaments driven by the weibel or current filamentation instability. | magnetized current filaments as a source of circularly polarized light |
grb201214b is a weak gamma-ray burst discovered by fermi gbm and localized by swift bat close to a nearby galaxy at d~280 mpc. xrt follow-up observations do not identify any counterpart within the bat error region, showing that this event is not associated with a bright x-ray afterglow. its weak gamma-ray signal, lack of early x-ray emission and possible association with a nearby galaxy are reminiscent of grb150101b and gw170817, two off-axis afterglows detected by chandra. if grb201214b is a similar explosion seen off-axis, its afterglow would slowly rise and peak several days/weeks after the grb. we therefore request a pair of chandra observations to search for the onset of a delayed x-ray afterglow, and test whether this grb heralds a rare neutron star merger in the nearby universe. | grb201214b: an off-axis burst in the nearby universe? |
xmm-newton carried out a target of opportunity observation of grb 231115a (mereghetti et al., gcn 35037; fermi gbm team, gcn 35035) which is likely a magnetar giant flare in the m82 galaxy (d'avanzo et al., gcn 35036; burns, gcn 35038) and was also detected by glowbug (cheung et al., gcn 35045), insight-hxmt (xue et al., gcn 35060), konus-wind (frederiks et al. gcn 35062) and swift/bat (ronchini et al., gcn 35065). the burst location was observed with the epic instrument on 2023-11-16 from 08:27 ut to 21:19 ut (to+16.8 hr to to+29.7 hr). a large fraction of the ~46 ks long observation was affected by high background, resulting in cleaned exposure times of 8.4 ks for the pn camera and 19.0 and 23.6 ks for the mos1 and mos2 cameras, respectively. comparison of images in various energy ranges with those of the epic observations of m82 in 2021 and 2022, does not reveal any new source inside the integral ibas error circle (2 arcmin radius, mereghetti et al., gcn 35037). for about 50% of the error region, we derived a 3 sigma count rate upper limit of 0.004 pn cts/s in the 2-10 kev energy range. for an absorbed power law spectrum with photon index 2 and n_h=6.5e20 cm-2 this corresponds to about 3e-14 erg/cm2/s (2-10 kev). diffuse x-ray emission from the central part of m82 affects the error region, resulting in limits higher than 0.01 pn cts/s (2-10 kev) in less than 20% of the error region. the lack of detection of an x-ray afterglow associated to grb 231115a in the xmm-newton observation 16.8 hours after the trigger provides further evidence that the burst is likely a magnetar giant flare in the m82 galaxy. | grb 231115a: xmm-newton observation |
low-luminosity gamma-ray bursts (grbs) have small isotropic equivalent gamma-ray energy and luminosity, compared with normal long grbs. grb 190829a is a member of this class. furthermore, very-high-energy gamma-rays were detected by h.e.s.s. with ∼ 20σ significance. this event had more unusual features. first, it had much smaller isotropic equivalent gamma-ray energy than typical long gamma-ray bursts and is classified as low-luminosity grb. second, early x-ray and optical afterglow emission showed a rising part and simultaneously peaked at about 1400 s. we propose an off-axis jet scenario that explains these observational results. in this model, the relativistic beaming effect is responsible for the apparently small isotropic gamma-ray energy and spectral peak energy. using a jetted afterglow model, we find that the narrow jet, which has the initial lorentz factor of 350 and the initial jet opening half-angle of 0.015 rad, viewed off-axis can describe the observed achromatic behavior in the x-ray and optical afterglow. another wide, baryon-loaded jet is necessary for the later-epoch x-ray and radio emissions. derived parameters explains the very-high-energy gamma-ray flux at 20,000 s. | off-axis jet scenario for early afterglow emission of low-luminosity gamma-ray burst grb 190829a |
at 10:59:30 ut, the swift burst alert telescope (bat) triggered and located grb 201229a (trigger=1015088). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 210.708, +48.197 which is ra(j2000) = 14h 02m 50s dec(j2000) = +48d 11' 50" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 7 sec. the peak count rate was ~500 counts/sec (15-350 kev), at ~2 sec after the trigger. the xrt began observing the field at 11:01:22.2 ut, 111.4 seconds after the bat trigger. using promptly downlinked data we find a fading, uncatalogued x-ray source with an enhanced position: ra, dec 210.6891, 48.1976 which is equivalent to: ra(j2000) = 14h 02m 45.39s dec(j2000) = +48d 11' 51.2" with an uncertainty of 2.2 arcseconds (radius, 90% containment). this location is 45 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 1.78 x 10^20 cm^-2 (willingale et al. 2013). uvot took a finding chart exposure of 150 seconds with the white filter starting 116 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 14:02:45.41 = 210.68921 dec(j2000) = +48:11:53.8 = 48.19828 with a 90%-confidence error radius of about 0.62 arc sec. this position is 3.1 arc sec. from the center of the xrt error circle. the estimated magnitude is 18.19 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.01. burst advocate for this burst is b. sbarufatti (bxs60 at psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 201229a: swift detection of a burst with a possible optical counterpart |
at 14:44:31 ut, the swift burst alert telescope (bat) triggered and located grb 200127a (trigger=952791). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 295.204, +44.910 which is ra(j2000) = 19h 40m 49s dec(j2000) = +44d 54' 35" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). as is usual with an image trigger, the available bat light curve shows no significant structure. the xrt began observing the field at 14:46:52.1 ut, 140.5 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source located at ra, dec 295.19447, 44.90030 which is equivalent to: ra(j2000) = 19h 40m 46.67s dec(j2000) = +44d 54' 01.1" with an uncertainty of 3.5 arcseconds (radius, 90% containment). this location is 42 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 2.17 x 10^21 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 9.40e-10 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 250 seconds with the u filter starting 309 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.2 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18.0 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.16. burst advocate for this burst is m. j. moss (mikejmoss3 at gmail.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200127a: swift detection of a burst |
at 22:41:15 ut, the swift burst alert telescope (bat) triggered and located grb 200131a (trigger=953689). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 3.095, +51.124 which is ra(j2000) = 00h 12m 23s dec(j2000) = +51d 07' 25" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 5 sec. there might be a small pulse at t+30 s. the peak count rate was ~60000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 22:42:24.7 ut, 68.7 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 3.0942, 51.1158 which is equivalent to: ra(j2000) = 00h 12m 22.61s dec(j2000) = +51d 06' 56.9" with an uncertainty of 4.9 arcseconds (radius, 90% containment). this location is 29 arcseconds from the bat onboard position, within the bat error circle. no event data are yet available to determine the column density using x-ray spectroscopy. the initial flux in the 2.5 s image was 3.76e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 77 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 00:12:22.57 = 3.09403 dec(j2000) = +51:07:00.4 = 51.11678 with a 90%-confidence error radius of about 0.61 arc sec. this position is 3.6 arc sec. from the center of the xrt error circle. the estimated magnitude is 15.44 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.17. burst advocate for this burst is b. sbarufatti (bxs60 at psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200131a: swift detection of a burst with an optical counterpart |
swift-xrt has performed follow-up observations of the integral/spi-acs and swift-bat guano detected possible short burst grb 200405b (james delaunay et al. gcn circ. 27497), collecting 5.0 ks of photon counting (pc) mode data between t0+66.6 ks and t0+80.0 ks. four uncatalogued x-ray sources have been detected, however none of them is above the rass limit or shows definitive signs of fading. therefore, at the present time we cannot identify which, if any, is the afterglow. we note that source 2 lies within the 4 arcmin bat error region reported in gcn circ. 27497. details of these sources are given below: source 1: ra (j2000.0): 62.6009 = 04:10:24.21 dec (j2000.0): -51.4435 = -51:26:36.5 error: 5.5 arcsec (radius, 90% conf.) count-rate: (1.87 [+0.90, -0.69])e-3 ct s^-1 distance: 530 arcsec from bat position. flux: (1.15 [+0.55, -0.43])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 2: ra (j2000.0): 62.8248 = 04:11:17.95 dec (j2000.0): -51.5687 = -51:34:07.5 error: 6.5 arcsec (radius, 90% conf. [enhanced position]) count-rate: (3.31 [+1.13, -0.93])e-3 ct s^-1 distance: 152 arcsec from bat position. flux: (4.1 [+1.4, -1.1])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 3: ra (j2000.0): 62.5137 = 04:10:3.28 dec (j2000.0): -51.4509 = -51:27:03.3 error: 4.6 arcsec (radius, 90% conf.) count-rate: (1.96 [+0.97, -0.73])e-3 ct s^-1 distance: 684 arcsec from bat position. source 4: ra (j2000.0): 62.6146 = 04:10:27.49 dec (j2000.0): -51.5329 = -51:31:58.3 error: 4.3 arcsec (radius, 90% conf.) count-rate: (3.74 [+1.18, -0.99])e-3 ct s^-1 distance: 391 arcsec from bat position. flux: (1.20 [+0.38, -0.32])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/00020979. this circular is an official product of the swift-xrt team. | grb 200405b: swift-xrt observations |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 201104a (ohno et al. gcn circ. 28828) in a series of observations tiled on the sky. the total exposure time is 4.7 ks, distributed over 3 tiles; the maximum exposure at a single sky location was 2.4 ks. the data were collected between t0+67.6 ks and t0+80.9 ks, and are entirely in photon counting (pc) mode. one uncatalogued x-ray source has been detected, it is not above the rass limit or shows definitive signs of fading. furthermore, it is coincident with a known optical source and the xrt data are possibly affected by stray light. therefore we believe that xrt has not detected any viable candidate afterglow. details of the sources are given below: source 3: ra (j2000.0): 80.9041 = 05:23:36.99 dec (j2000.0): -71.0096 = -71:00:34.6 error: 4.1 arcsec (radius, 90% conf. [enhanced position]) count-rate: (5.3 [+2.7, -2.0])e-3 ct s^-1 distance: 664 arcsec from fermi/lat position. flux: (1.53 [+0.77, -0.59])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) a catalogued source was also detected inside the lat error circle, and two more sources were detected outside of it. the 3 sigma upper limit at the lat grb position is 7.6×10-3 ct s-1. the results of the xrt-team automatic analysis of the tiled xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/tiled_grb00094. this circular is an official product of the swift-xrt team. | grb 201104a: swift-xrt observations |
at 19:10:18 ut on 29 november 2023, the atmosphere-space interactions monitor (asim) mission triggered on the long bright grb 231129c. the burst was also detected by fermi-gbm (sharma et al., gcn circ. 35221, and sharma et al., gcn circ. 227), maxi/gsc (kawakubo et al., gcn circ. 35223), calet (shimizu et al., gcn circ. 35228), astrosat czti (waratkar et al., gcn circ. 35230), gecam-b (zheng et al., gcn circ. 35231), swift-xrt (gropp et al., gcn circ. 35234), glowbug (cheung et al., gcn circ. 35235), grbalpha (dafcikova et al., gcn circ. 35236), fermi-lat (arimoto et al., gcn circ. 35238, agile (panebianco et al., gcn circ. 35244), and konus-wind (lysenko et al., gcn circ. 35256). photon by photon data with <1 microsecond time resolution have been collected for a time interval of 19 seconds. the emission is detected in the mxgs high energy detector (hed), sensitive in the range 0.3 to >30 mev, and in the mxgs low energy detector (led), sensitive in the range 0.05 to 0.4 mev. in january 2022 asim was relocated so that the mxgs coded mask imaging system is pointing towards the earth's limb, observing a large fraction of unocculted sky, therefore enabling localization of the grb prompt emission. this grb was observed within the mxgs field of view resulting in a very high significant localization (>100 sigma) at r.a.,dec(2000) = 00:51:12.56 -81:45:35.5 consistent within a 25 arcmin error (radius, 99% confidence level) with the swift-xrt x-ray afterglow (gropp et al., gcn circ. 35251) and the master ot detection (antipov et al., gcn circ.35240). asim is an esa mission onboard the international space station dedicated to the observation of terrestrial gamma-ray flashes (tgfs) and transient luminous events (tles) operative since june 2018 (neubert et al., space sci rev (2019) 215:26 https://doi.org/10.1007/s11214-019-0592-z ). the payload includes the modular x- and gamma-ray sensor (mxgs) (østgaard et al., space sci rev (2019) 215:23 https://doi.org/10.1007/s11214-018-0573-7 ), and the the modular multispectral imaging array (mmia) (chanrion et al., space sci rev (2019) 215:28 https://doi.org/10.1007/s11214-019-0593-y ). the asim science data centre (asdc) website is https://asdc.space.dtu.dk/ | grb 231129c: asim mxgs observation and localization |
at 15:43:52 ut, the swift burst alert telescope (bat) triggered and located grb 200819a (trigger=992099). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 21.428, +63.048 which is ra(j2000) = 01h 25m 43s dec(j2000) = +63d 02' 52" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 10 sec. the peak count rate was ~1600 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 15:45:17.4 ut, 84.5 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 21.4240, 63.0614 which is equivalent to: ra(j2000) = 01h 25m 41.76s dec(j2000) = +63d 03' 40.9" with an uncertainty of 2.6 arcseconds (radius, 90% containment). this location is 48 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 9.84 x 10^21 cm^-2 (willingale et al. 2013). uvot took a finding chart exposure of 150 seconds with the white filter starting 88 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the large, but uncertain, extinction expected. we note that this source is near the galactic plane (lat=0.45, lon=126.8 degrees) which raises the possibility that this is a new galactic transient. the source is somewhat soft (visible above 50 kev but not above 100 kev). the lightcurve is consistent with either a grb or a galactic transient. the complete dataset from this event and further observations of the source will determine the nature of this source. if it is a galactic transient we would name it swift j0125.7+6303 . burst advocate for this burst is s. dichiara (dichiara at umd.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200819a: swift detection of a burst |
at 07:09:26 ut, the swift burst alert telescope (bat) triggered and located grb 200901b (trigger=994165). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 217.879, -38.716 which is ra(j2000) = 14h 31m 31s dec(j2000) = -38d 42' 58" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). as is usual with an image trigger, the available bat light curve shows no significant structure. the xrt began observing the field at 07:12:16.1 ut, 169.7 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 217.8572, -38.7117 which is equivalent to: ra(j2000) = 14h 31m 25.73s dec(j2000) = -38d 42' 42.1" with an uncertainty of 5.5 arcseconds (radius, 90% containment). this location is 63 arcseconds from the bat onboard position, within the bat error circle. no event data are yet available to determine the column density using x-ray spectroscopy. the initial flux in the 2.5 s image was 1.11e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 250 seconds with the u filter starting 175 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.2 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18.0 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.09. burst advocate for this burst is b. sbarufatti (bxs60 at psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200901b: swift detection of a burst |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 201020b (arimoto et al. gcn circ. 28716), collecting 1.7 ks of photon counting (pc) mode data between t0+72.1 ks and t0+74.3 ks. an uncatalogued x-ray source is detected and is above the rass limit, and is therefore likely the grb afterglow. using 1015 s of pc mode data and 2 uvot images, we find an enhanced xrt position (using the xrt-uvot alignment and matching uvot field sources to the usno-b1 catalogue): ra, dec = 75.46680, +77.06830 which is equivalent to: ra (j2000): 05h 01m 52.03s dec(j2000): +77d 04' 05.9" with an uncertainty of 2.0 arcsec (radius, 90% confidence). this position is 9.6 arcmin from the fermi/lat position and consistent with the optical counterpart detected by master (lipunov et al. gcn circ. 28718). the light curve is consistent with a constant source of mean count rate 1.5e-01 ct/sec. with the currently available dataset we cannot constrain the temporal evolution. a spectrum formed from the pc mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+0.4, -0.3). the best-fitting absorption column is 4.0 (+1.7, -1.4) x 10^21 cm^-2, in excess of the galactic value of 1.4 x 10^21 cm^-2 (willingale et al. 2013). the counts to observed (unabsorbed) 0.3-10 kev flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1. a summary of the pc-mode spectrum is thus: total column: 4.0 (+1.7, -1.4) x 10^21 cm^-2 galactic foreground: 1.4 x 10^21 cm^-2 excess significance: 3.0 sigma photon index: 2.2 (+0.4, -0.3) the results of the xrt-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/too_grbs/00021035/source1.php. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021035. this circular is an official product of the swift-xrt team. | grb 201020b: swift-xrt afterglow detection |
"at 03:34:26.00 ut on 03 august 2020, the fermi gamma-ray burst monitor (gbm) triggered and located grb 200803a (trigger 618118471 / 200803149) which was also detected by the fermi/lat (cutini et al. 2020, gcn 28203). the fermi gbm final real-time localization (gcn 28196) is consistent with the lat position. an x-ray afterglow candidate has been detected by the swift/xrt (gcn 28205), and a potential optical counterpart has also been reported by master (gcn 28202). the angle from the fermi lat boresight at the gbm trigger time is ~39 degrees. the gbm light curve consists of two main pulses with a duration (t90) of about 119 s (50-300 kev). the time-averaged spectrum of the first pulse, from t0-4 s to t0+14 s is best fit by a power law function with an exponential high-energy cutoff. the power law index is -0.67 +/- 0.04 and the cutoff energy, parameterized as epeak, is 302 +/- 13 kev. the event fluence (10-1000 kev) in this time interval is (1.12 +/- 0.03)e-05. the time-averaged spectrum of the second pulse, from t0+85 s to t0+118 s is also best fit by a power law function with an exponential high-energy cutoff. the power law index is -1.13 +/- 0.02 and the cutoff energy, parameterized as epeak, is 223 +/- 8 kev. the event fluence (10-1000 kev) in this time interval is (1.84 +/- 0.03)e-05. the 1-sec peak photon flux measured starting from t0+112 s in the 10-1000 kev band is 10.8 +/- 0.3 ph/s/cm^2. the spectral analysis results presented above are preliminary; final results will be published in the gbm grb catalog: https://heasarc.gsfc.nasa.gov/w3browse/fermi/fermigbrst.html for fermi gbm data and info, please visit the official fermi gbm support page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" | grb 200803a: fermi gbm detection |
swift-xrt has performed follow-up observations of the swift-bat-detected burst grb 231110a, collecting 10 ks of photon counting (pc) mode data between t0+8.9 ks and t0+61.1 ks. four uncatalogued x-ray sources are detected consistent with being within 296 arcsec of the swift-bat position, of which one ("source 2") is believed to be the afterglow. the position of this source is ra, dec=356.2752, +82.6447 which is equivalent to: ra (j2000): 23:45:6.05 dec(j2000): +82:38:40.9 with an uncertainty of 5.1 arcsec (radius, 90% confidence). this position is 85 arcsec from the swift-bat position. there is evidence that the source may be fading, however we cannot constrain the decay at the current time the results of the xrt-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01195733. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/01195733. this circular is an official product of the swift-xrt team. | grb 231110a: swift-xrt afterglow detection |
at 22:57:08 ut, the swift burst alert telescope (bat) triggered and located grb 210807c (trigger=1064421). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 143.551, -51.409 which is ra(j2000) = 09h 34m 12s dec(j2000) = -51d 24' 31" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). although the lightcurve before t+8s is not currently available due to a telemetry dropout, the later lightcurve shows a complex structure extending at least to t+90s. the peak count rate in the available lightcurve was ~800 counts/sec (15-350 kev), at ~20 sec after the trigger. the xrt began observing the field at 23:00:05.5 ut, 177.1 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 143.53455, -51.40237 which is equivalent to: ra(j2000) = 09h 34m 08.29s dec(j2000) = -51d 24' 08.5" with an uncertainty of 7.1 arcseconds (radius, 90% containment). this location is 43 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. a power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. the initial flux in the 2.5 s image was 2.31e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 250 seconds with the v filter starting 180 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.2 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18.0 mag. no correction has been made for the large, but uncertain, extinction expected. burst advocate for this burst is a. y. lien (amy.y.lien at nasa.gov). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210807c: swift detection of a burst |
at 23:52:59 ut, the swift burst alert telescope (bat) triggered and located grb 190630c (trigger=912239). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 293.908, -32.751 which is ra(j2000) = 19h 35m 38s dec(j2000) = -32d 45' 03" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a single-peaked structure with a duration of about 120 sec. the peak count rate was ~2000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 23:55:28.8 ut, 149.3 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source located at ra, dec 293.87874, -32.74273 which is equivalent to: ra(j2000) = 19h 35m 30.90s dec(j2000) = -32d 44' 33.8" with an uncertainty of 3.8 arcseconds (radius, 90% containment). this location is 93 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. no spectrum from the promptly downlinked event data is yet available to determine the column density. the initial flux in the 2.5 s image was 1.02e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 157 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.11. this source lies within the current (sector 13) field-of-view of tess camera 1. burst advocate for this burst is t. n. ukwatta (tilan.ukwatta at gmail.com). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 190630c: swift detection of a burst |
at 14:17:19 ut, the swift burst alert telescope (bat) triggered and located grb 231111a (trigger=1195887). swift slewed immediately to the event. the bat on-board calculated location is ra, dec 290.234, +52.447 which is ra(j2000) = 19h 20m 56s dec(j2000) = +52d 26' 49" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). due to a telemetry outage, there is no immediately available bat lightcurve information. however the trigger information indicates an initial count rate of 3100 counts/s (25-100 kev) on a 1 second timescale. the xrt began observing the field at 14:18:59.3 ut, 99.6 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 290.1915, 52.4383 which is equivalent to: ra(j2000) = 19h 20m 45.96s dec(j2000) = +52d 26' 17.9" with an uncertainty of 5.5 arcseconds (radius, 90% containment). this location is 98 arcseconds from the bat onboard position, within the bat error circle. no event data are yet available to determine the column density using x-ray spectroscopy. uvot took a finding chart exposure of 238 seconds with the u filter starting 164 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 19:20:45.24 = 290.18848 dec(j2000) = +52:26:10.5 = 52.43626 with a 90%-confidence error radius of about 0.62 arc sec. this position is 9.9 arc sec. from the center of the xrt error circle. the estimated magnitude is 16.51 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.117. burst advocate for this burst is a. melandri (andrea.melandri at inaf.it). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 231111a: swift detection of a burst with an optical counterpart |
at 23:32:06 ut, the swift burst alert telescope (bat) triggered and located grb 211227a (trigger=1091101). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 132.126, -2.702 which is ra(j2000) = 08h 48m 30s dec(j2000) = -02d 42' 05" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 100 sec. the peak count rate was ~5200 counts/sec (15-350 kev), at ~1 sec after the trigger. the xrt began observing the field at 23:33:20.3 ut, 73.5 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source located at ra, dec 132.14898, -2.73556 which is equivalent to: ra(j2000) = 08h 48m 35.76s dec(j2000) = -02d 44' 08.0" with an uncertainty of 3.8 arcseconds (radius, 90% containment). this location is 146 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (2.37 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 4.3 (+3.24/-2.79) x 10^21 cm^-2 (90% confidence). the initial flux in the 2.5 s image was 6.84e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 81 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.020. burst advocate for this burst is a. p. beardmore (apb at star.le.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 211227a: swift detection of a burst |
we have analysed 7.8 ks of photon counting (pc) mode xrt data for the swift-bat-detected burst grb 220412b (gropp et al. gcn circ. 31886), collected between t0+4.7 ks and t0+29.1 ks. no x-ray sources have been detected consistent with being within 296 arcsec of the swift-bat position. the 3-sigma upper limit in the field is 0.001 ct s^-1, corresponding to a 0.3-10 kev observed flux of 4.2e-14 erg cm^-2 s^-1 (assuming a typical grb spectrum). four uncatalogued sources were detected too far from the grb position to be likely afterglow candidates. the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/01102329. this circular is an official product of the swift-xrt team. | grb 220412b: swift-xrt observations |
swift-xrt has performed follow-up observations of the possible hawc-detected burst grb 191210a (https://gcn.gsfc.nasa.gov/notices_amon_hawc/9066_1171.amon) in a series of observations tiled on the sky. the total exposure time is 8.1 ks, distributed over 20 tiles; the maximum exposure at a single sky location was 948 s. the data were collected between t0+7.0 ks and t0+30.1 ks, and are entirely in photon counting (pc) mode. four uncatalogued x-ray sources have been detected, however none of them is above the rass limit or shows definitive signs of fading. therefore, at the present time we cannot identify which, if any, is the afterglow. details of these sources are given below: source 1: ra (j2000.0): 210.3973 = 14:01:35.35 dec (j2000.0): -0.7503 = -00:45:01.1 error: 10.2 arcsec (radius, 90% conf.) count-rate: (3.8 [+6.0, -2.9])e-3 ct s^-1 distance: 3115 arcsec from hawc position. source 2: ra (j2000.0): 210.1243 = 14:00:29.84 dec (j2000.0): -1.3003 = -01:18:01.1 error: 10.5 arcsec (radius, 90% conf.) count-rate: 0.019 [+0.017, -0.011] ct s^-1 distance: 2561 arcsec from hawc position. source 4: ra (j2000.0): 211.3249 = 14:05:17.98 dec (j2000.0): -1.9738 = -01:58:25.8 error: 6.0 arcsec (radius, 90% conf.) count-rate: 0.0139 [+0.0102, -0.0069] ct s^-1 distance: 2502 arcsec from hawc position. source 5: ra (j2000.0): 210.6745 = 14:02:41.89 dec (j2000.0): -1.9321 = -01:55:55.6 error: 8.4 arcsec (radius, 90% conf.) count-rate: 0.0110 [+0.0081, -0.0054] ct s^-1 distance: 1572 arcsec from hawc position. a catalogued source was also detected. the results of the xrt-team automatic analysis of the tiled xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/tiled_grb00087. this circular is an official product of the swift-xrt team. | possible hawc-detected grb 191210a: swift-xrt observations |
we have analysed 3.8 ks of photon counting (pc) mode xrt data for the swift/bat-detected burst grb 190816a (page et al. gcn circ. 25368), collected between t0+141.7 ks and t0+216.6 ks. one uncatalogued x-ray source has been detected consistent with being within 296 arcsec of the swift/bat position, it is below the rass limit and shows no definitive signs of fading. therefore, at the present time we cannot confirm this as the afterglow. details of this source are given below: source 4: ra (j2000.0): 341.1897 = 22:44:45.53 dec (j2000.0): -29.7577 = -29:45:27.8 error: 4.8 arcsec (radius, 90% conf. [enhanced position]) count-rate: (8.1 [+1.8, -1.7])e-3 ct s^-1 distance: 64 arcsec from swift/bat position. flux: (2.67 [+0.60, -0.56])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) three uncatalogued sources were also detected too far from the grb position to be likely afterglow candidates. the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/00920783. this circular is an official product of the swift-xrt team. | grb 190816a: swift-xrt observations |
at 20:24:28 ut, the swift burst alert telescope (bat) triggered and located grb 231214a (trigger=1202386). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 305.736, -72.436 which is ra(j2000) = 20h 22m 57s dec(j2000) = -72d 26' 09" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a double-peaked structure with a duration of about 30 sec. the peak count rate was ~8000 counts/sec (15-350 kev), at ~13 sec after the trigger. the xrt began observing the field at 20:26:14.5 ut, 106.2 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 305.68573, -72.43256 which is equivalent to: ra(j2000) = 20h 22m 44.58s dec(j2000) = -72d 25' 57.2" with an uncertainty of 1.9 arcseconds (radius, 90% containment). this location is 56 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. no spectrum from the promptly downlinked event data is yet available to determine the column density. uvot took a finding chart exposure of 39 seconds with the white filter starting 442 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.060. burst advocate for this burst is r. brivio (riccardo.brivio at inaf.it). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 231214a: swift detection of a burst |
at 12:49:20 ut, the swift burst alert telescope (bat) triggered and located grb 170516a (trigger=753110). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 41.598, -55.899, which is ra(j2000) = 02h 46m 24s dec(j2000) = -55d 53' 54" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve shows a couple peaks with a total duration of about 35 sec. the peak count rate was ~1500 counts/sec (15-350 kev), at ~3 sec after the trigger. the xrt began observing the field at 12:50:41.1 ut, 80.5 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 41.5663, -55.9092 which is equivalent to: ra(j2000) = +02h 46m 15.91s dec(j2000) = -55d 54' 33.1" with an uncertainty of 6.4 arcseconds (radius, 90% containment). this location is 73 arcseconds from the bat onboard position, within the bat error circle. the initial flux in the 2.5 s image was 4.96e-10 erg cm^-2 s^-1 (0.2-10 kev). automated uvot data processing is currently not working, but manual inspection of the uvot image shows no grb afterglow counterpart. burst advocate for this burst is a. y. lien (amy.y.lien at nasa.gov). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/too.html.) | grb 170516a: swift detection of a burst |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 210826a (ohno et al. gcn circ. 30721), for a total exposure time of 4.9 ks. the data were collected between t0+36.5 ks and t0+49.7 ks, and are entirely in photon counting (pc) mode. eight uncatalogued x-ray sources have been detected, however none of them is above the rass limit or shows definitive signs of fading. therefore, at the present time we cannot identify which, if any, is the afterglow. we notice that one of the sources (source 8) is consistent with a catalogued galaxy at redshift z = 0.05. details of these sources are given below: source 1: ra (j2000.0): 45.3361 = 03:01:20.66 dec (j2000.0): -71.7072 = -71:42:25.8 error: 8.7 arcsec (radius, 90% conf.) count-rate: (1.46 [+0.80, -0.61])e-3 ct s^-1 distance: 48 arcsec from fermi/lat position. source 2: ra (j2000.0): 45.0955 = 03:00:22.93 dec (j2000.0): -71.6531 = -71:39:11.1 error: 5.0 arcsec (radius, 90% conf. [enhanced position]) count-rate: (3.06 [+1.16, -0.94])e-3 ct s^-1 distance: 286 arcsec from fermi/lat position. flux: (8.2 [+3.1, -2.5])e-14 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 4: ra (j2000.0): 45.1820 = 03:00:43.67 dec (j2000.0): -71.5711 = -71:34:15.8 error: 9.7 arcsec (radius, 90% conf.) count-rate: (1.36 [+0.80, -0.59])e-3 ct s^-1 distance: 483 arcsec from fermi/lat position. flux: (8.2 [+4.8, -3.6])e-14 erg cm^-2 s^-1 (observed, 0.3-10 kev) this source is 10" away from the agn candidate wisea j030045.23-713422.8 (assef et al., 2018, apjs, 234, 23) source 5: ra (j2000.0): 45.4777 = 03:01:54.65 dec (j2000.0): -71.6539 = -71:39:13.9 error: 8.4 arcsec (radius, 90% conf.) count-rate: (3.7 [+1.3, -1.0])e-3 ct s^-1 distance: 260 arcsec from fermi/lat position. flux: (5.8 [+2.0, -1.6])e-14 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 6: ra (j2000.0): 45.1850 = 03:00:44.41 dec (j2000.0): -71.7836 = -71:47:00.9 error: 10.0 arcsec (radius, 90% conf.) count-rate: (1.60 [+0.86, -0.65])e-3 ct s^-1 distance: 327 arcsec from fermi/lat position. flux: (4.2 [+2.2, -1.7])e-14 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 7: ra (j2000.0): 45.3683 = 03:01:28.39 dec (j2000.0): -71.6617 = -71:39:42.1 error: 10.3 arcsec (radius, 90% conf.) count-rate: (1.54 [+0.84, -0.63])e-3 ct s^-1 distance: 158 arcsec from fermi/lat position. this source is 6" away from the agn candidate wisea j030129.33-713938.6 (assef et al., 2018, apjs, 234, 23) source 8: ra (j2000.0): 44.7903 = 02:59:9.68 dec (j2000.0): -71.6112 = -71:36:40.2 error: 9.3 arcsec (radius, 90% conf.) count-rate: (1.11 [+0.78, -0.56])e-3 ct s^-1 distance: 660 arcsec from fermi/lat position. this source is 9" away from the catalogued galaxy 2masx j02591150-7136430 at redshift z = 0.05 source 9: ra (j2000.0): 45.6834 = 03:02:44.02 dec (j2000.0): -71.6574 = -71:39:26.7 error: 8.8 arcsec (radius, 90% conf.) count-rate: (2.16 [+1.02, -0.79])e-3 ct s^-1 distance: 460 arcsec from fermi/lat position. flux: (8.1 [+3.8, -3.0])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) the results of the xrt-team automatic analysis of the tiled xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/tiled_grb00101. this circular is an official product of the swift-xrt team. | grb 210826a: swift-xrt observations |
fast radio bursts (frbs) are an emerging class of most likely extragalactic astrophysical transients whose physical origin remains a mystery. in spitler et al. (2016), we reported the discovery of the first repeating frb using arecibo, which we have subsequently detected with the gbt multiple times as well. this extraordinary discovery offers a unique opportunity to determine the nature of the underlying sources responsible for frbs. to this end, we propose a set of coordinated chandra acis-i and gbt observations, to establish if frbs are accompanied by x-ray flashes or short-lived afterglows. detection of correlated x-ray emission with chandra would constrain the energetics of the frb source and provide arcsecond localization, which would enable definitive association with a host galaxy. | coordinated x-ray and radio observations of the repeating fast radio burst frb 121102 |
at 19:49:15 ut, the swift burst alert telescope (bat) triggered and located grb 170524a (trigger=754322). swift slewed immediately to the source. the bat on-board calculated location is ra, dec 319.456, +48.587, which is ra(j2000) = 21h 17m 49s dec(j2000) = +48d 35' 15" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve shows a single peak with a duration of about 0.25 sec. the peak count rate was ~3000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 19:50:16.0 ut, 60.7 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 319.4869, 48.6065 which is equivalent to: ra(j2000) = 21h 17m 56.86s dec(j2000) = +48d 36' 23.4" with an uncertainty of 4.1 arcseconds (radius, 90% containment). this location is 101 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. a power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. uvot took a finding chart exposure of 150 seconds with the white filter starting 67 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the large, but uncertain extinction expected. we note that this is a short burst, close to the galactic plane (lat = -0.5 degrees), although far from the galactic center (lon = 91 degrees). thus there is a possibility that this is a previously unknown soft gamma repeater (sgr). however, the preliminary 4-energy lightcurve shows more flux above 100 kev than is typical for an sgr burst. burst advocate for this burst is j.g. gropp (jdg44 at psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/too.html.) | grb 170524a: swift detection of a burst (or possible new sgr) |
at 06:19:20 ut, the swift burst alert telescope (bat) triggered and located grb 220518a (trigger= 1107050). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 55.369, -47.571 which is ra(j2000) = +03h 41m 29s dec(j2000) = -47d 34' 15" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). there are currently no bat light curve data available at this time. the xrt began observing the field at 06:21:27.1 ut, 126.4 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 55.34297, -47.58392 which is equivalent to: ra(j2000) = 03h 41m 22.31s dec(j2000) = -47d 35' 02.1" with an uncertainty of 1.9 arcseconds (radius, 90% containment). this location is 78 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (9.33 x 10^19 cm^-2, willingale et al. 2013), with an excess column of 5 (+3.25/-2.72) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 129 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers none of the xrt error circle. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.008. burst advocate for this burst is j.d. gropp (jdg44 at psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 220518a: swift detection of a burst |
using the 0.92m asiago schmidt telescope, we observed the field of grb 190613b 11.954 h after the burst (d'ai et al. gcn 24807) in g, r and i. we detected a source consistent with the optical and x-ray afterglow (burgess et al. gcn 24808, beardmore et al. gcn 24812, bissaldi et al. gcn 24814, marshall et al. gcn 24817, zheng & filippenko gcn 24818, ukwatta et al. gcn 24820, page et al. gcn 24823) in g band images while we could only set upper limits in the other bands. the measured magnitude and 2.5-sigma upper limits are listed below: filter t_start t_stop jd_avg exp(s) mag g 2019-06-13t22:44:17 2019-06-13t23:02:00 58647.95239 180*5 21.40 +/- 0.30 r 2019-06-13t23:02:14 2019-06-13t23:20:00 58647.96488 180*5 > 20.1 i 2019-06-13t23:23:32 2019-06-13t23:34:38 58647.97735 180*5 > 20.4 | grb 190613b: optical observation from asiago schmidt |
at 21:52:08 ut, the swift burst alert telescope (bat) triggered and located grb 210207b (trigger=1031297). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 270.582, +53.694 which is ra(j2000) = 18h 02m 20s dec(j2000) = +53d 41' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 100 sec. the peak count rate was ~2500 counts/sec (15-350 kev), at ~45 sec after the trigger. the xrt began observing the field at 21:53:22.0 ut, 73.9 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 270.6356, 53.6836 which is equivalent to: ra(j2000) = 18h 02m 32.54s dec(j2000) = +53d 41' 01.0" with an uncertainty of 4.7 arcseconds (radius, 90% containment). this location is 120 arcseconds from the bat onboard position, within the bat error circle. no event data are yet available to determine the column density using x-ray spectroscopy. the initial flux in the 2.5 s image was 1.09e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 82 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 18:02:32.40 = 270.63501 dec(j2000) = +53:40:56.0 = 53.68223 with a 90%-confidence error radius of about 0.74 arc sec. this position is 5.1 arc sec. from the center of the xrt error circle. the estimated magnitude is 13.72 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.041. burst advocate for this burst is a. y. lien (amy.y.lien at nasa.gov). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210207b: swift detection of a burst with a bright optical counterpart |
swift-xrt has performed follow-up observations of the maxi-detected burst grb 221008a (soejima et al. gcn circ. 32630) in a series of observations tiled on the sky. the total exposure time is 1.2 ks, distributed over 4 tiles; the maximum exposure at a single sky location was 466 s. the data were collected between t0+50.0 ks and t0+51.4 ks, and are entirely in photon counting (pc) mode. no uncatalogued x-ray sources have been detected. the 3-sigma upper limit in the field (not including the regions where the tiles overlap) ranges from ~0.03 to ~0.06 ct s^-1, corresponding to a 0.3-10 kev observed flux of 1.1e-12 to 2.4e-12 erg cm^-2 s^-1 (assuming a typical grb spectrum). a previously-catalogued x-ray source has been detected, however because it is a catalogued object it is unlikely to be the afterglow. the results of the xrt-team automatic analysis of the tiled xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/tiled_grb00109. this circular is an official product of the swift-xrt team. | grb 221008a: swift-xrt observations |
i present a study of the mass-metalliciy (mz) relation in a redshift range of z ∼ 0.3-3.4 using 33 star-forming galaxies selected by gamma ray bursts (grbs) with emission metallicity measurements. grbs are beacons of star-forming galaxies up to very high redshifts. the detectability of these extremely bright anddust-penetrating explosions is independent of the brightness and dust content of their host galaxies. hence faint galaxies are not missed when selected by grbs. i show that grb host galaxies remarkably follow the mz relation of the general star-forming population with considering the redshift evolution of the mz relation. while our results confirm the mz relation and its evolution at z>2, they also suggest grb hosts as obvious candidates for studying the mz relation and its evolution at high redshifts. the presence of grb afterglows provide accurate metallicity measurements for grb host galaxies up to very high redshifts (z∼6);. these measurements are based on absorption profiles and hence do not suffer from calibration issues. in addition it is confirmed now that though at z<1.5 grb hosts appear to follow the low mass end of the luminosity function, at higher redshifts they sample the star-forming galaxy population. i discuss the possibility of using grb hosts with absorption metallicity measurements to investigate the mz relation at high redshifts. | tracing the mass-metallicity relation of star-forming galaxies at high redshifts using grb-selected galaxies |
"we re-observed the position of short grb 210726a (bernardini et al., gcn 30523; veres et al., gcn 30540; palmer et al., gcn 30536; tohuvavohu et al., gcn 30535) with the karl g. jansky very large array (vla) under program 20b-057 (pi: fong) beginning on 2021 august 07.02 ut (11.21 days post-burst) at a mean frequency of 6 ghz. in 1.5 hour of observations we detect a radio source with a preliminary flux density of ~40 ujy. the position of this radio source is fully consistent with the position of the x-ray afterglow (osborne et al., gcn 30524; rouco escorial et al., gcn 30558) at: ra(j2000): 12:53:09.8 dec(j2000): +19:11:25.1 with an uncertainty of 0.6 arcsec in each coordinate. we obtained further vla observations at 6 ghz and 10 ghz beginning on 2021 august 14.75 ut (18.94 days post-burst) and detect the source at both frequencies. we find a significant brightening at 6 ghz, confirming this source as the radio afterglow of grb210726a. we note that this radio afterglow is among the brightest ever detected for a short grb to date. further observations are planned. we thank the vla staff for quickly approving and executing these observations." | grb 210726a: vla radio afterglow detection |
swift-xrt has performed follow-up observations of the integral-detected burst grb 190919b (mereghetti et al. gcn circ. 25788), collecting 3.0 ks of photon counting (pc) mode data between t0+28.6 ks and t0+36.4 ks. an uncatalogued x-ray source has been detected 1.1 arcsec from the reported grond afterglow position (bolmer, gcn circ. 25789): source 1: ra (j2000.0): 311.87783 = 20:47:30.68 dec (j2000.0): -44.69542 = -44:41:43.5 error: 2.1 arcsec (radius, 90% conf. [enhanced position]) count-rate: 0.0222 [+0.0032, -0.0031] ct s^-1 distance: 0 arcsec from integral position. flux: (7.16 [+1.03, -0.98])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) the source is below the rass limit and, due to the limited amount of data available so far, shows no signs of fading. the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/00020948. this circular is an official product of the swift-xrt team. | grb 190919b: swift-xrt observations |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 201208a (dirirsa et al. gcn circ. 29003), collecting 5.0 ks of photon counting (pc) mode data between t0+70.4 ks and t0+111.4 ks. four uncatalogued x-ray sources are detected, of which one ("source 2") is above the 2sxps 3-sigma upper limit at this position, and is therefore likely the grb afterglow. using 2046 s of pc mode data and 2 uvot images, we find an enhanced xrt position (using the xrt-uvot alignment and matching uvot field sources to the usno-b1 catalogue): ra, dec = 158.32352, -28.71989 which is equivalent to: ra (j2000): 10h 33m 17.64s dec(j2000): -28d 43' 11.6" with an uncertainty of 3.1 arcsec (radius, 90% confidence). this position is 112 arcsec from the fermi/lat position. the results of the xrt-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/too_grbs/00021405/source2.php. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021405. this circular is an official product of the swift-xrt team. | grb 201208a: swift-xrt afterglow detection |
at 08:42:38 ut, the swift burst alert telescope (bat) triggered and located grb 210307a (trigger=1036139). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 119.190, -66.963 which is ra(j2000) = 07h 56m 46s dec(j2000) = -66d 57' 45" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure with a duration of about 120 sec. the peak count rate was ~1300 counts/sec (15-350 kev), at ~3 sec after the trigger. the xrt began observing the field at 96.2 s seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with a position: ra, dec 119.239583, -66.969694 which is equivalent to: ra(j2000) = 07 56 57.5 dec(j2000) = -66 58 10.9 with an uncertainty of 4.7 arcseconds (radius, 90% containment). this location is 73.8 arcsec from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. uvot took a finding chart exposure of 150 seconds with the white filter starting 100 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.138. this source lies within the current (sector 35) field-of-view of tess camera 4. burst advocate for this burst is e. ambrosi (elena.ambrosi at inaf.it). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210307a: swift detection of a burst |
swift-xrt has performed follow-up observations of the swift/bat-detected burst grb 210605b (james delaunay et al. gcn circ. 30130), collecting 5.0 ks of photon counting (pc) mode data between t0+74.2 ks and t0+96.6 ks. one uncatalogued x-ray sources has been detected, however it is not above the rass limit or shows definitive signs of fading. therefore, at the present time we cannot confirm if this source is the afterglow. details of the source are given below: source 1: ra (j2000.0): 15.7456 = 01:02:58.95 dec (j2000.0): -6.4290 = -06:25:44.3 error: 5.7 arcsec (radius, 90% conf.) count-rate: (2.94 [+1.05, -0.86])e-3 ct s^-1 distance: 145 arcsec from swift/bat position. flux: (9.3 [+3.3, -2.7])e-14 erg cm^-2 s^-1 (observed, 0.3-10 kev) the field has been previously observed by xrt for the swift gravitational wave galaxy survey (https://www.swift.ac.uk/sgwgs/). no source was detected at this position on a 5.3 ks integrated exposure, down to a 3-σ upper limit of 2.7 e-3 ct s^-1. a catalogued source and a spurious source caused by earth limb contamination were also detected. the results of the xrt-team automatic analysis of the xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/too_grbs/00021450. this circular is an official product of the swift-xrt team. | grb 210605b: swift-xrt observations |
swift-xrt has performed follow-up observations of the ipn-detected burst grb 201227a (ursi et al. gcn circ. 29179) in a series of observations tiled on the sky. the total exposure time is 7.5 ks, distributed over 4 tiles; the maximum exposure at a single sky location was 5.3 ks. the data were collected between t0+51.6 ks and t0+80.7 ks, and are entirely in photon counting (pc) mode. four uncatalogued x-ray sources have been detected, however none of them is above the rass limit or shows definitive signs of fading. therefore, at the present time we cannot identify which, if any, is the afterglow. details of these sources are given below: source 1: ra (j2000.0): 170.6083 = 11:22:25.99 dec (j2000.0): -73.4880 = -73:29:16.9 error: 7.4 arcsec (radius, 90% conf.) count-rate: (4.4 [+1.7, -1.4])e-3 ct s^-1 distance: 670 arcsec from ipn position. flux: (9.0 [+3.5, -2.8])e-14 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 2: ra (j2000.0): 170.6190 = 11:22:28.57 dec (j2000.0): -73.4798 = -73:28:47.2 error: 4.8 arcsec (radius, 90% conf.) count-rate: (3.6 [+1.6, -1.3])e-3 ct s^-1 distance: 698 arcsec from ipn position. flux: (1.34 [+0.60, -0.47])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 3: ra (j2000.0): 169.8508 = 11:19:24.19 dec (j2000.0): -73.5866 = -73:35:11.9 error: 5.6 arcsec (radius, 90% conf.) count-rate: (2.8 [+1.4, -1.1])e-3 ct s^-1 distance: 290 arcsec from ipn position. source 4: ra (j2000.0): 171.2953 = 11:25:10.87 dec (j2000.0): -73.6326 = -73:37:57.4 error: 4.4 arcsec (radius, 90% conf.) count-rate: (4.2 [+2.6, -1.9])e-3 ct s^-1 distance: 1194 arcsec from ipn position. the results of the xrt-team automatic analysis of the tiled xrt observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/tiled_grb00096. this circular is an official product of the swift-xrt team. | grb 201227a: swift-xrt observations |
swift-xrt has performed follow-up observations of the swift/bat-guano-detected burst grb 220107a (delaunay et al. gcn circ. 31402), collecting 699 s of photon counting (pc) mode data between t0+26.7 ks and t0+27.4 ks. an uncatalogued x-ray source is detected and is above the rass 3-sigma upper limit at this position, and is therefore likely the grb afterglow. using 698 s of pc mode data and 1 uvot image, we find an enhanced xrt position (using the xrt-uvot alignment and matching uvot field sources to the usno-b1 catalogue): ra, dec = 169.80648, +34.17014 which is equivalent to: ra (j2000): 11h 19m 13.55s dec(j2000): +34d 10' 12.5" with an uncertainty of 2.3 arcsec (radius, 90% confidence). this position is 3.0 arcmin from the swift/bat-guano position. the light curve can be modelled with a power-law decay with a decay index of alpha=2.5 (+0.5, -2.4). a spectrum formed from the pc mode data can be fitted with an absorbed power-law with a photon spectral index of 1.84 (+0.27, -0.18). the best-fitting absorption column is 3.1 (+6.1, -0.9) x 10^20 cm^-2, consistent with the galactic value of 2.2 x 10^20 cm^-2 (willingale et al. 2013). the counts to observed (unabsorbed) 0.3-10 kev flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (3.7 x 10^-11) erg cm^-2 count^-1. a summary of the pc-mode spectrum is thus: total column: 3.1 (+6.1, -0.9) x 10^20 cm^-2 galactic foreground: 2.2 x 10^20 cm^-2 excess significance: <1.6 sigma photon index: 1.84 (+0.27, -0.18) if the light curve continues to decay with a power-law decay index of 2.5, the count rate at t+24 hours will be 0.054 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 kev flux of 1.9 x 10^-12 (2.0 x 10^-12) erg cm^-2 s^-1. the results of the xrt-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021476. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021476. this circular is an official product of the swift-xrt team. | grb 220107a: swift-xrt afterglow detection |
swift-xrt has performed further follow-up observations of the fermi/gbm (e. bissaldi et al. gcn 30405) and swift/bat-guano detected burst grb 210706a (tohuvavohu et al., gcn circ. 30393), collecting 9.5 ks of photon counting (pc) mode data between t0+43 ks and t0+180 ks. the uncatalogued x-ray source (src #2) detected in the first 2.8 ks of data as the grb afterglow candidate (tohuvavohu et al. gcn 30399), which was above existing upper limits at this location from previous xrt observations, has faded significantly in the latest observation, and is thus confirmed as the x-ray afterglow of the burst. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/xrt_curves/00021455/. this circular is an official product of the swift-xrt team. | grb 210706a: swift/xrt afterglow confirmation |
at 15:49:44 ut, the swift burst alert telescope (bat) triggered and located grb 180102a (trigger=802999). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 203.115, +62.148 which is ra(j2000) = 13h 32m 28s dec(j2000) = +62d 08' 53" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 40 sec. the peak count rate was ~1800 counts/sec (15-350 kev), at ~1 sec after the trigger. the xrt began observing the field at 15:50:54.4 ut, 70.2 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 203.06761, 62.17091 which is equivalent to: ra(j2000) = 13h 32m 16.23s dec(j2000) = +62d 10' 15.3" with an uncertainty of 3.8 arcseconds (radius, 90% containment). this location is 114 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 1.88 x 10^20 cm^-2 (willingale et al. 2013). uvot took a finding chart exposure of 150 seconds with the white filter starting 73 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers none of the xrt error circle. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.01. burst advocate for this burst is k. l. page (klp5 at leicester.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/too.html.) | grb 180102a: swift detection of a burst |
at 15:28:49 ut, the swift burst alert telescope (bat) triggered and located grb 200806a (trigger=987016). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 52.905, +37.082 which is ra(j2000) = 03h 31m 37s dec(j2000) = +37d 04' 55" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a pulse that starts at ~t0 and lasts beyond the currently available data, which ends at ~t+8 s. the peak count rate was ~4800 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 15:30:07.6 ut, 77.7 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source located at ra, dec 52.93173, 37.07845 which is equivalent to: ra(j2000) = 03h 31m 43.62s dec(j2000) = +37d 04' 42.4" with an uncertainty of 3.5 arcseconds (radius, 90% containment). this location is 77 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 2.56 x 10^21 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 2.59e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 86 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.42. burst advocate for this burst is e. ambrosi (elena.ambrosi at inaf.it). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200806a: swift detection of a burst |
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