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nicer observed the rapidly fading transient at2022cva (ho et al. gcn 31619) for 2.4 ks starting at 2022-02-21t22:56:03. x-rays are clearly detected above the background in the 0.3-5.0 kev band with a mean background-subtracted count rate of 0.92+-0.02 counts/seconds. | nicer x-ray detection of ztf22aabjpxh/at2022cva are consistent with a grb afterglow at z=0.293 |
at 03:15:35 ut, the swift burst alert telescope (bat) triggered and located grb 230325a (trigger=1161390). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 296.820, -46.094 which is ra(j2000) = 19h 47m 17s dec(j2000) = -46d 05' 38" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a complex structure structure with a duration of about 40 sec. the peak count rate was ~2200 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 03:17:09.9 ut, 94.0 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source located at ra, dec 296.84910, -46.07455 which is equivalent to: ra(j2000) = 19h 47m 23.78s dec(j2000) = -46d 04' 28.4" with an uncertainty of 3.8 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. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (4.88 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 3.9 (+3.24/-2.71) x 10^21 cm^-2 (90% confidence). the initial flux in the 2.5 s image was 2.06e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 101 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 0.046. 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 230325a: swift detection of a burst |
gw170817/grb 170817a has had a huge impact on our understanding of gamma-ray burst (grb) afterglows, and has prompted a huge sustained effort at modeling the details of the geometry and emission from grb jets. while no additional electro-magnetic counterparts have been detected to gravitational wave emission from neutron star mergers so far, it is certainly reasonable to expect further detections in the future. whether these will be very similar in nature to grb 170817a or instead will provide us with samplings of afterglow model parameters across a wide parameter space remains an open question. in this presentation i will survey some of the work done by the various active groups worldwide in theoretical modeling and understanding afterglows post 170817a. | grb 170817a and the long-term aftermath of neutron star mergers |
in the first observed neutron star merger, gw170817, two dynamical components, mildly- and ultra-relativistic outflows were detected independently. the first component triggered a rapidly evolving thermal transient named macronova (kilonova), while the second caused an observed short grb where the early gamma-ray signal was followed by a multi-wavelength afterglow. these two distinct components are typically modelled independently and the observational consequences of their interplay are hardly explored. here we summarize the results of 3d special-relativistic simulations that we have used to investigate the consequences of jet propagation through a realistic environment. we show how the presence of a jet can lead to the macronova being brighter and bluer for on-axis observers in the first few days. then we show the consequences on the interaction on the shape of the emerging jet. finally, we will discuss how small scale features in the emerging jet structure can impact the best-fit afterglow parameters. | consequences of jet-ejecta interaction in neutron star mergers |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 231222b in a series of observations tiled on the sky. we point out that the burst was improperly named grb 231222a in gcn circ 35415, where the tiling was announced. the total exposure time is 4.1 ks, distributed over 4 tiles; the maximum exposure at a single sky location was 2.3 ks. the data were collected between t0+43.2 ks and t0+54.8 ks, and are entirely in photon counting (pc) mode. three uncatalogued x-ray sources are detected, of which one ("source 1") is believed to be the afterglow. using 1211 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 = 251.24744, +19.62084 which is equivalent to: ra (j2000): 16h 44m 59.39s dec(j2000): +19d 37' 15.0" with an uncertainty of 3.3 arcsec (radius, 90% confidence). this position is 9.3 arcmin from the fermi/lat position. the source has a mean count rate of 6.0e-02 ct/sec; we cannot determine at the present time whether it is fading. a spectrum formed from the pc mode data can be fitted with an absorbed power-law with a photon spectral index of 1.65 (+0.49, -0.29). the best-fitting absorption column is consistent with the galactic value of 7.1 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 3.4 x 10^-11 (3.8 x 10^-11) erg cm^-2 count^-1. a summary of the pc-mode spectrum is thus: total column: 7 (+/-14) x 10^20 cm^-2 galactic foreground: 7.1 x 10^20 cm^-2 excess significance: <1.6 sigma photon index: 1.65 (+0.49, -0.29) the results of the xrt-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021639. the results of the full analysis of the tiled xrt observations are available at https://www.swift.ac.uk/xrt_products/tiled_grb00118. this circular is an official product of the swift-xrt team. | grb 231222b: swift-xrt afterglow detection |
the gamma-ray bursts (grbs) with distinct thermal components are rarely detected, especially in cases with thermal components throughout the prompt phase. recently, fermi/gbm, swift/bat, and swift/xrt detected the special long-duration grb 190109a, which has four pulses in the prompt gamma-ray emission, i.e, pulse i (-4 to 20 s), pulse ii (20-50 s), pulse iii (50-90 s), and pulse iv (90-120 s). grb 190109a exhibits a very hard low-energy index (α ~ 1) in the band function relative to the typical grbs (α ~ - 1). in the whole burst prompt emission, we find distinct thermal emissions in the time-resolved spectra throughout four pulses. the blackbody (bb) temperature kt varies from 24.7 to 8.2 kev for pulse i to pulse iv. we also obtain the relation of f ∝ kt -0.40 for the early phase (pulse i) and f ∝ kt 3.33±0.76 for the late phase (pulses ii-iv), respectively. the significant deviation of the kt - f relation in the early epochs from that in the late epochs likely suggests that the bb spectra origin of the early phase (pulse i) may have disparate physical processes from those of the late phase (pulses ii-iv). for instance, it may be the transition from cocoon surroundings by a jet to the photosphere of the matter-dominated jet. a jet break is found in the late x-ray afterglow, which is in keeping with the standard external shock afterglow model in the interstellar medium circumburst. | distinct thermal emission from grb 190109a |
the full-frame images produced by the transiting exoplanet survey satellite (tess) are invaluable tools to detect periodic and transient astrophysical events, such as variable stars, supernovae, tidal disruption events, and gamma-ray burst afterglows. our pixel-level method separates the time-series ffis into smaller groups and then calculates the per-pixel variance over the duration of each group. these variance maps are then combined across adjacent groups to produce a "variability" image in which systematics, like those caused by scattered light and differential velocity aberration, are mitigated. all point sources in the variability image are extracted and classified using a convolutional neural network (cnn) that has been trained on known transients from tess's prime mission. our cnn has 90% accuracy on test data, which will increase as newly-identified transients are added to the training set. sources with the highest probabilities (assigned through classification) are filtered by matching with catalogs like simbad and tns, and photometry is done on the set of filtered sources. the generated light curves are then analyzed using a variety of statistical techniques to prioritize those that are most important for follow-up. we are thus able to filter the tens to hundreds of thousands of point sources in each variability image to a manageable level (100s per sector) that can then be visually inspected prior to follow-up. our technique has also shed light on detector systematics that must be mitigated to increase our pipeline's snr. future work will involve exploiting the novel 10-minute ffis to evaluate transient light curves in finer detail. additionally, we hope to identify tess-band counterparts to high-energy transient events, such as compact object mergers and frbs, that have large error ellipses. | using machine learning to detect transients in tess ffis |
we forecast the reionization history constraints, inferred from lyman-alpha damping wing absorption features, for a future sample of ~ 20 z > 6 gamma-ray burst (grb) afterglows using a fisher matrix analysis. we determine the expected constraints on the average neutral fraction after marginalizing over parameters describing the size of the ionized regions around each grb and the column density of local damped lyman-alpha systems associated with the grb host galaxies. assuming follow-up spectroscopy of the afterglows with a fiducial signal-to-noise ratio of 20 per r=3,000 resolution element at the continuum, we find that the neutral fraction may be determined to better than 10-15% (1-sigma) accuracy from this data across multiple independent redshift bins at z ~ 6-10, spanning much of the epoch of reionization, although the precision degrades somewhat near the end of reionization. a more futuristic survey with 80 grb afterglows at z > 6 can improve the precision here by a factor of 2 and extend measurements out to z ~ 14. | future constraints on the reionization history from grb afterglows |
swift-xrt has performed follow-up observations of the maxi-detected burst grb 221006a (mihara et al. gcn circ. 32626) in a series of observations tiled on the sky. the total exposure time is 1.9 ks, distributed over 3 tiles; the maximum exposure at a single sky location was 992 s. the data were collected between t0+37.6 ks and t0+39.8 ks, and are entirely in photon counting (pc) mode. three 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): 337.3524 = 22:29:24.58 dec (j2000.0): +15.6341 = +15:38:02.8 error: 12.1 arcsec (radius, 90% conf.) count-rate: 0.0104 [+0.0063, -0.0045] ct s^-1 distance: 262 arcsec from maxi position. source 2: ra (j2000.0): 337.2458 = 22:28:58.99 dec (j2000.0): +15.7138 = +15:42:49.6 error: 3.2 arcsec (radius, 90% conf. [enhanced position]) count-rate: 0.0401 [+0.0076, -0.0070] ct s^-1 distance: 287 arcsec from maxi position. flux: (1.67 [+0.32, -0.29])e-12 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 3: ra (j2000.0): 337.3461 = 22:29:23.07 dec (j2000.0): +15.6941 = +15:41:38.6 error: 8.2 arcsec (radius, 90% conf.) count-rate: 0.0106 [+0.0043, -0.0034] ct s^-1 distance: 70 arcsec from maxi position. flux: (2.00 [+0.81, -0.64])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_grb00108. this circular is an official product of the swift-xrt team. | grb 221006a: swift-xrt observations |
the study of gamma-ray burst (grb) afterglows across the electromagnetic spectrum can reveal a lot of information about their jets and surrounding environment. the physical parameters of the grb jet and emission processes at its shock front can be constrained by broad-band modeling, but individual parameters can in some cases be determined by a limited number of observables, which can be used to independently constrain the models themselves. we expand upon a method using peaks observed in afterglow radio light curves to constrain the fraction of the shock energy that resides in electrons, ɛe,weakly depending on other physical parameters. we use both light curves and radio spectra to determine the peaks, allowing for a systematic check of the modeling approach. we also expand the sample of 36 radio afterglows in the initial study with 15 additional grbs that have good radio data available. with this expanded methodology and larger sample, we assess the initial results on the width of the distribution of ɛe,which provides important input on grb shock physics. | making the most of radio peaks in gamma-ray burst afterglows |
gamma-ray bursts (grbs) are panchromatic phenomena by nature; their afterglow emissions are observed from sub-tev energies to radio wavelengths. in this work, we investigate grbs presenting the plateau feature in optical observations, inspired by the similarities with the plateau feature in x-ray observations. we analyze all published grbs with optical plateaus and known redshifts, observed mostly by the neil gehrels swift observatory. we fit 277 optical light curves using the willingale 2007 phenomenological model and find the plateau exists in 102 cases. in addition to exploring trends in optical wavelengths, we also compare the rest-frame end-time of the plateau in optical and x-ray wavelengths (t*opt, t*x) for 56 grbs with observations at both wavelengths; we find that there is an indication of achromaticity between t*opt and t*x. we also confirm the existence of the two-dimensional dainotti relation between t*opt and the optical luminosity lopt at the end of the plateau emission for our sample, which is the largest compilation of optical plateaus thus far. we find that the optical correlation has the smallest scatter for grbs associated spectroscopically with sne ib/c, where the scatter is 48.7% smaller than that of the total sample. | the optical luminosity-time correlation for 102 gamma-ray burst afterglows |
grb 210205a was detected by the swift burst alert telescope (bat) at 11:11:17 ut on 5th feb 2021 (gcn 29397). the prompt emission mask-weighted bat light curve consists of a multi-peaked structure with a t90 duration of 22.70 +- 4.18 sec in 15-350 kev energy range (gcn 29409). we compare the reported value of bat fluence and peak photon flux for this grb (gcn 29409) with all the bat detected samples, we find this burst is positioned nearly the middle of this distribution. the swift xrt detected an x-ray afterglow ~ 134.7 sec after the bat trigger (gcn 29397). the x-ray light curve could be best described with a simple power-law model with a temporal index of 1.100 (+0.092, -0.101) and the afterglow is fainter (0.016 x 10^-11 erg/cm2/s, at 11-hour post burst) than typical x-ray afterglows. as no red-shift has been reported for this source, we modeled the time-averaged xrt spectrum (t0 + 143 to 39716 s) considering red-shift = 2, roughly average red-shift value for long grbs. the spectrum could be modeled using an absorption power-law with following spectral parameters: nh_host= 5.34 (-4.58,+6.18) * 10^{22} cm^{-2} and \beta_x= 1.11 (-0.37,+0.40). considering the adiabatic deceleration without energy injection, closure relations indicate that the x-ray afterglow could be best described with \nu > \nu_c spectral regime for ism as well as wind medium for the electron energy index p ~ 2.22. many optical telescopes searched for the optical afterglow but no counterpart associated with this burst was detected to deeper limits at early epochs(gcn 29397, 29398, 29400, 29401, 29402, 29403, and 29406). so, we performed the search for the optical counterpart of this xrt localized grb 210205a (gcn 29399) using the 4kx4k ccd imager (pandey et al. 2017, arxiv:1711.05422v1) mounted at the axial port of the 3.6m devasthal optical telescope (dot) of aries nainital. multiple frames having exposure times of 300s each were taken in r and i filters. we do not find any evidence of an afterglow candidate inside the xrt error circle, consistent with other non-detections. we constrain the following 3-sigma upper limits. t-t0 (days) exp. (s) filter ot ul telescope 1.0921 2*300 r na 22.8 3.6m dot 1.1033 2*300 i na 22.6 3.6m dot the limiting magnitudes quoted are not corrected for the galactic and host extinction in the direction of the burst. considering no spectral break between x-ray and optical frequencies, we extrapolated the x-ray spectral index towards optical frequencies. we found that using reported limiting values at optical (galactic extinction corrected) roughly lie below the extrapolated x-ray power-law slope, suggesting that this burst could be a potential dark grb candidate either highly extinguished or as a high redshift event. 3.6m devasthal optical telescope (dot) is a recently commissioned facility in the northern himalayan region of india (long:79 41 04e, lat:29 21 40n, alt:2540m) owned and operated by the aryabhatta research institute of observational sciences (aries), nainital (https://www.aries.res.in). authors of this gcn circular thankfully acknowledge consistent support from the staff members to run and maintain the 3.6m dot. this circular may be cited. | grb 210205a: observations with the 3.6m dot, a potential dark burst? |
the distribution of jet angles for short gamma-ray bursts (sgrbs) is critical to constrain because it directly affects the true energy scale and event rate. the event rate is of particular interest in the gravitational wave era. our current knowledge of the jet angle distribution comes almost exclusively from x-ray observations at >1 day after the burst. here, we propose for chandra too observations to monitor an sgrb afterglow and constrain its collimation, either from the detection of a jet break, or the non-detection of a break to place a lower limit of >5-20 deg. a precise calculation of the jet angle also requires broad-band afterglow observations, which will be leveraged to provide the tightest constraints on the jet angle. | the late-time x-ray behavior of short gamma-ray bursts: implications for energetics and rates |
at 06:36:50 ut, the swift burst alert telescope (bat) triggered and located grb 220412a (trigger=1102281). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 123.968, +30.322 which is ra(j2000) = 08h 15m 52s dec(j2000) = +30d 19' 19" 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 ~900 counts/sec (15-350 kev), at ~1 sec after the trigger. the xrt began observing the field at 06:38:52.9 ut, 122.7 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 123.96470, 30.34319 which is equivalent to: ra(j2000) = 08h 15m 51.53s dec(j2000) = +30d 20' 35.5" with an uncertainty of 4.5 arcseconds (radius, 90% containment). this location is 76 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 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 0.037. burst advocate for this burst is n. j. klingler (noelklin at umbc.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 220412a: swift detection of a burst |
swift-xrt has performed follow-up observations of the swift/bat-guano-detected burst grb 210706a (tohuvavohu et al. gcn circ. 30393), collecting 2.8 ks of photon counting (pc) mode data between t0+43.3 ks and t0+50.7 ks. two uncatalogued x-ray sources are detected, of which one ("source 2") is believed to be the afterglow. using 2536 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 = 311.99471, +13.31694 which is equivalent to: ra (j2000): 20h 47m 58.73s dec(j2000): +13d 19' 01.0" with an uncertainty of 3.2 arcsec (radius, 90% confidence). this position is 69 arcsec from the swift/bat-guano position. the source has a mean count rate of 1.4e-02 ct/sec; we cannot determine at the present time whether it is fading. the field has been previously observed by xrt for the swift gravitational wave galaxy survey (https://www.swift.ac.uk/sgwgs/, gcn 24305). no source was detected at this position on a 2.8 ks integrated exposure, down to a 3-σ upper limit of 7 e-3 ct s^-1. the results of the xrt-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021455. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021455. this circular is an official product of the swift-xrt team. | grb 210706a: swift-xrt afterglow detection |
at 01:37:03 ut, the swift burst alert telescope (bat) triggered and located grb 210112a (trigger=1016881). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 218.999, +33.070 which is ra(j2000) = 14h 36m 00s dec(j2000) = +33d 04' 13" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve shows multiple peaks with the larger peak at t+70 sec and duration of ~150 sec. the peak count rate was ~20800 counts/sec (15-350 kev), at ~68 sec after the trigger. the xrt began observing the field at 01:38:18.0 ut, 74.2 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 219.0044, 33.0566 which is equivalent to: ra(j2000) = 14h 36m 1.06s dec(j2000) = +33d 03' 23.8" with an uncertainty of 5.0 arcseconds (radius, 90% containment). this location is 50 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 7.10e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 82 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 14:36:01.45 = 219.00606 dec(j2000) = +33:03:15.4 = 33.05428 with a 90%-confidence error radius of about 0.66 arc sec. this position is 9.8 arc sec. from the center of the xrt error circle. the estimated magnitude is 19.52 with a 1-sigma error of about 0.16. no correction has been made for the expected extinction corresponding to e(b-v) of 0.014. 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 210112a: swift detection of a burst with an optical counterpart |
gw170817 was detected almost 4.5 years ago as the first binary neutron star (bns) merger by the ligo/virgo collaboration. it is the first object to have both a gravitational wave and an electromagnetic counterpart and it also provided the first observational confirmation of the connection between short gamma-ray bursts and bns mergers. it still remains the only one of its kind. for almost 3 years, the evolution of the broadband non-thermal emission originating in gw170817 was consistent with an afterglow produced by the interaction of an ultra-relativistic structured jet, that was initially viewed off-axis, with the ambient medium. however, observations 3.4 years after the merger narrated a story different from expectations. we observed a statistically significant excess in x-rays compared to the predictions from a structured jet model, which was not accompanied by an excess in radio. i will discuss our investigation of a few theoretical models that could lead to a deviation from the existing model in x-rays only, including the plausibility of an emerging kilonova afterglow, which if true, would make it the first ever to be observed. i will discuss an alternate scenario where the x-ray excess is powered by the accretion onto a black hole remnant. i will further present the most recent observations we acquired ∼4.5 years after the merger and our preliminary interpretations of them. | emergence of a new x-ray emission component from gw170817 3.5 years after the merger |
at 08:43:18 ut, the swift burst alert telescope (bat) triggered and located grb 210211a (trigger=1032024). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 269.433, -46.299 which is ra(j2000) = 17h 57m 44s dec(j2000) = -46d 17' 57" 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 10 sec. the peak count rate was ~2500 counts/sec (15-350 kev), at ~4 sec after the trigger. the xrt began observing the field at 08:44:32.2 ut, 73.9 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 269.4374, -46.2660 which is equivalent to: ra(j2000) = 17h 57m 44.99s dec(j2000) = -46d 15' 57.7" with an uncertainty of 3.4 arcseconds (radius, 90% containment). this location is 119 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 (1.24 x 10^21 cm^-2, willingale et al. 2013), with an excess column of 8.7 (+9.04/-6.57) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 77 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 expected extinction corresponding to e(b-v) of 0.126. 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 210211a: swift detection of a burst |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 210802a (longo et al. gcn circ. 30589) in a series of observations tiled on the sky. the total exposure time is 5.2 ks, distributed over 4 tiles; the maximum exposure at a single sky location was 2.3 ks. the data were collected between t0+41.7 ks and t0+43.0 ks, and are entirely in photon counting (pc) mode. twenty-eight uncatalogued x-ray sources are detected. many of these sources are in the bottom tile (likely a high background effect), and in the left tile (possibly an extended emission related to a nearby cluster of galaxies). one of the most significant sources ("source 7") is above the 2sxps 3-sigma upper limit at this position, and is therefore likely the grb afterglow. using 1246 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 = 230.72285, +29.90180 which is equivalent to: ra (j2000): 15h 22m 53.48s dec(j2000): +29d 54' 06.5" with an uncertainty of 3.5 arcsec (radius, 90% confidence). this position is 9.8 arcmin from the fermi/lat position. while we cannot determine at the present time whether the source is fading, we note that a previous 1 ks swift-xrt visit of the field showed no sign of source 7 (https://www.swift.ac.uk/2sxps/fields/10000004351). the results of the xrt-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/xrt_products/tiled_grb00100/source7.php. the results of the full analysis of the tiled xrt observations are available at https://www.swift.ac.uk/xrt_products/tiled_grb00100. this circular is an official product of the swift-xrt team. | grb 210802a: swift-xrt afterglow detection |
at 00:10:13 ut, the swift burst alert telescope (bat) triggered and located a burst form the soft gamma repeater sgr 1830-0645 (trigger=1032350). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 277.660, -6.748 which is ra(j2000) = 18h 30m 38s dec(j2000) = -06d 44' 52" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a single short peak in one 0.128 s timebin. the peak count rate was ~8000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 00:11:14.4 ut, 60.6 seconds after the bat trigger. using promptly downlinked data we find an x-ray source with an enhanced position: ra, dec 277.6734, -6.7541 which is equivalent to: ra(j2000) = 18h 30m 41.61s dec(j2000) = -06d 45' 14.9" with an uncertainty of 2.2 arcseconds (radius, 90% containment). this location is 52 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 8.1 (+9.28/-7.67) x 10^21 cm^-2 (90% confidence). 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 25% of the bat 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 bat 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's most recent detection of this sgr was on 2020-11-22, following its discovery by swift on 2020-11-10 (page et al., gcn circ. 28594). | swift trigger 1032350: detection of sgr 1830-0645 |
we report the discovery of the fast optical transient ztf21aahifke/at2021clk with the zwicky transient facility (ztf, bellm et al. 2019, graham et al. 2019) at coordinates (j2000, <0.5''): ra = 02:54:27.54 (43.61475d) dec = +36:31:56.80 (+36.53244d) ztf21aahifke was first detected on 2021-02-06 03:14 ut, hereafter labelled t_det. it faded by ~0.9 mag in r-band in the first 24 hours since t_det. the transient was last detected by ztf on 2021-02-07 03:58 ut at r = 20.9 +- 0.2 mag. upper limits constrain the transient onset time to be within ~1 day from t_det. the color of the transient appears to be red, with g-r~0.3 (un-corrected) at t_det. the galactic extinction on the line of sight is e(b-v)=0.12 mag (planck collaboration et al., 2015). ztf21aahifke is located at galactic latitude b_gal = -20.1 deg. in the table below, we report photometry obtained using forcephotztf (yao et al., 2019) 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 ------------------------------------- 2021-02-05 04:53 | > 20.6 | - | g 2021-02-06 03:14 | 20.2 | 0.1 | g 2021-02-06 04:16 | 19.9 | 0.1 | r 2021-02-07 03:58 | 20.9 | 0.2 | r 2021-02-09 03:59 | > 21.0 | - | r ------------------------------------- forced photometry on 1109 ztf images taken before t_det did not reveal any previous activity. previous activity was also not found in the pan-starrs (chambers et al., 2016) dr2 catalog and in atlas images, explored via the public forced photometry server (tonry et al., 2018; smith et al., 2020). a possible host galaxy, sdss j025427.89+363151.5 (r=21.4), is located ~6.6 arcsec away from ztf21aahifke. the source has sdss photometric redshift of zphot = 0.433 +- 0.1735. we do not find any fermi-identified gamma-ray bursts consistent with the detection location and explosion time of this object, assuming that a grb happened between the last non-detection and t_det. the nature of ztf21aahifke remains uncertain and we cannot exclude the possibility that it is the afterglow of an un-triggered (or off-axis) grb, or galactic in origin. follow-up observations are encouraged. ztf21aahifke was found by the ''ztf realtime search and triggering'' (ztfrest) 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. based on observations obtained with the samuel oschin telescope 48-inch and the 60-inch telescope at the palomar observatory as part of the zwicky transient facility project. ztf is supported by the national science foundation under grant no. ast-2034437 and a collaboration including caltech, ipac, the weizmann institute for science, the oskar klein center at stockholm university, the university of maryland, deutsches elektronen-synchrotron and humboldt university, the tango consortium of taiwan, the university of wisconsin at milwaukee, trinity college dublin, lawrence livermore national laboratories, and in2p3, france. operations are conducted by coo, ipac, and uw. | ztf21aahifke/at2021clk: ztf discovery of an optical fast transient (possible afterglow) |
at 03:54:31 ut, the swift burst alert telescope (bat) triggered and located grb 210318a (trigger=1037339). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 33.930, -37.789 which is ra(j2000) = 02h 15m 43s dec(j2000) = -37d 47' 21" 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 ~700 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 03:56:35.2 ut, 123.5 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 33.9263, -37.7772 which is equivalent to: ra(j2000) = 02h 15m 42.32s dec(j2000) = -37d 46' 38.1" with an uncertainty of 3.2 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 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 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 0.016. 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 210318a: swift detection of a burst |
at 15:05:51 ut, the swift burst alert telescope (bat) triggered and located grb 210411c (trigger=1042398). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 296.559, -39.373 which is ra(j2000) = 19h 46m 14s dec(j2000) = -39d 22' 21" 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. the peak count rate was ~5500 counts/sec (15-350 kev), at ~4 sec after the trigger. the xrt began observing the field at 15:06:54.6 ut, 63.1 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 296.60899, -39.39786 which is equivalent to: ra(j2000) = 19h 46m 26.16s dec(j2000) = -39d 23' 52.3" with an uncertainty of 3.7 arcseconds (radius, 90% containment). this location is 165 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 (8.10 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 3.2 (+2.66/-2.35) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of nominal 150.000 seconds with the white filter starting 66 seconds after the bat trigger. there is a candidate afterglow in the list of sources generated on-board at ra(j2000) = 19:46:26.83 = 296.61178 dec(j2000) = -39:23:51.9 = -39.39774 with a 90%-confidence error radius of about 1.10 arc sec. this position is 7.0 arc sec. from the center of the xrt error circle. the estimated magnitude is 17.99. no correction has been made for the expected extinction corresponding to e(b-v) of 0.080. burst advocate for this burst is t. sbarrato (tullia.sbarrato 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 210411c: swift detection of a burst with an optical counterpart |
swift-xrt has performed follow up observations of grb 210218a (sbarufatti et al. gcn circ. 29529). the swift-bat trigger happened while the burst position in the sky was moon constrained for xrt and uvot observations. a first follow up observation was performed when the target emerged from moon constraint, with one uncatalogued x-ray source (source #3) detected inside the bat error circle (sbarufatti et al. gcn circ. 29542). swift-xrt observed the field again, for a further 4.7 ks, from t+497 ks to t+549 ks. source #3 has faded below detection, with a 3-sigma upper limit of 2.5e-3 cts s^-1 (equivalent to 4.6e-14 erg cm^-2 s^-1 ), and is thus confirmed to be the burst afterglow. this circular is an official product of the swift-xrt team. | grb 210218a: swift-xrt confirmation of afterglow |
the radio observations of grbs presented in this paper were obtained using ami, which is a radio interferometer consisting of eight 12.8m diameter dishes with baselines between 18 and 110m. as all the observations were conducted prior to 2015 june, the effective frequency range was 13.9-17.5ghz using channels 3-7, each with a bandwidth of 0.72ghz, with channels 1, 2 and 8 being disregarded due to their susceptibility to radio frequency interference (rfi). through the ami grb follow-up programme, we have produced the first catalogue of radio afterglows that is representative (i.e. not biased by target selection informed by prior knowledge of the event) of the radio properties of swift-detected grbs down to 0.2mjy/beam at 15.7ghz. this catalogue includes 139 grbs, 132 of which were detected with swift, and is made up of ami observations up to >90d post-burst. (2 data files). | vizier online data catalog: ami 15.7ghz grb catalogue (anderson+, 2018) |
gamma-ray bursts (grbs) are panchromatic phenomena by nature; their afterglow emissions are observed from sub-tev energies to radio wavelengths. in this work, we investigate grbs presenting the plateau feature in optical observations, inspired by the similarities with the plateau feature in x-ray observations. we analyze all published grbs with optical plateaus and known redshifts, observed mostly by the neil gehrels swift observatory. we fit 277 optical light curves using the willingale 2007 phenomenological model and find the plateau exists in 102 cases. in addition to exploring trends in optical wavelengths, we also compare the rest-frame end-time of the plateau in optical and x-ray wavelengths (t*opt, t*x) for 56 grbs with observations at both wavelengths; we find that there is an indication of achromaticity between t*opt and t*x. we also confirm the existence of the two-dimensional dainotti relation between t*opt and the optical luminosity lopt at the end of the plateau emission for our sample, which is the largest compilation of optical plateaus thus far. we find that the optical correlation has the smallest scatter for grbs associated spectroscopically with sne ib/c, where the scatter is 48.7% smaller than that of the total sample. we also extend this correlation in 3d by adding the peak luminosity in the optical emission and we found out that it holds for more than 50 grbs. we will discuss the comparison with the previous 3d correlation in x-rays. we will also present future perspective with an observing program will soon initiate with the kiso observatory in japan for the optical follow-up of grbs. scientific goals of this project will be discussed. | the 3d optical fundamental plane as a further step of the luminosity-time correlation and future perspective with the kiso observatory |
at 01:53:02 ut on 2018 march 25, the neil gehrels swift observatory detected grb 180325a with its burst alert telescope (bat), and its x-ray telescope (xrt) began observations at 01:54:16.2 ut. at 6 minutes after the burst trigger, the nordic optical telescope (not) equipped with the andalucia faint object spectrograph and camera (alfosc) observed the grb in the r-band. the gamma-ray burst optical and near-infrared detector (grond) mounted at the 2.2m max planck gesellschaft telescope started taking photometric observations of the afterglow in all seven (g' r' i' z' jh and k) bands at ~1.05hr after the burst. we subsequently observed grb 180325a at ~1.84hr after trigger with the vlt/x-shooter spectrograph. vlt/x-shooter data were obtained as part of the stargate vlt proposal (program id: 0100.d-0649(a)). the complete log of grond, not, and vlt/x-shooter photometric observations is provided in table 1. (1 data file). | vizier online data catalog: grond, not & vlt/x-shooter obs. of grb180325a (zafar+, 2018) |
swift-xrt has performed follow-up observations of the swift/bat-guano-detected burst grb 210827a (james delaunay et al. gcn circ. 30732), collecting 2.3 ks of photon counting (pc) mode data between t0+44.4 ks and t0+50.4 ks. one uncatalogued x-ray source has been detected consistent with being within 296 arcsec of the swift/bat-guano 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 3: ra (j2000.0): 174.9003 = 11:39:36.07 dec (j2000.0): +55.7239 = +55:43:26.2 error: 3.8 arcsec (radius, 90% conf. [enhanced position]) count-rate: 0.0103 +/- 0.0025 ct s^-1 distance: 225 arcsec from swift/bat-guano position. flux: (4.8 +/- 1.2)e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) four 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/00021461. this circular is an official product of the swift-xrt team. | grb 210827a: swift-xrt observations |
at 07:20:08 ut, the swift burst alert telescope (bat) triggered and located grb 200227a (trigger=958592). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 56.436, +9.491 which is ra(j2000) = 03h 45m 45s dec(j2000) = +09d 29' 27" 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 ~4500 counts/sec (15-350 kev), at ~8 sec after the trigger. the xrt began observing the field at 07:21:30.1 ut, 82.2 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 56.43302, 9.48264 which is equivalent to: ra(j2000) = 03h 45m 43.92s dec(j2000) = +09d 28' 57.5" with an uncertainty of 3.5 arcseconds (radius, 90% containment). this location is 31 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 2.12 x 10^21 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 3.08e-09 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. 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 0.27. 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 200227a: swift detection of a burst |
electrons accelerated in relativistic collisionless shocks are usually assumed to follow a power-law energy distribution with an index of $p$. observationally, although most gamma-ray bursts (grbs) have afterglows that are consistent with $p>2$, there are still a few grbs suggestive of a hard ($p<2$) electron energy spectrum. our previous works found strong evidence for the exist of a double power-law hard electron energy (dplh) spectrum with $1<p_1<2$, $p_2>2$ and an injection break assumed as $\gamma_{\rm b}\propto \gamma^{q}$ in the relativistic regime. moreover, these works suggested a possibly universal value of $q\sim0.5$. grb~060908 is another case that shows a flat spectrum in the optical/near-infrared band and requires a hard electron energy distribution, which, along with the rich multi-band afterglow data, provides us an opportunity to test this conjecture. based on the model of \citet{resmi08}, we explain the multi-band afterglow of grb~060908 in a wind medium and take also the synchrotron self-compton effect. we show that though the dplh spectrum is favored by the afterglow data, the value of $q$ is badly constrained due to the relatively large uncertainties of the spectral indices. however, the afterglow can be well reproduced if we adopt $q=0.5$, implying the compatibility of the above conjecture with the data. | modeling the multi-band afterglow of grb 060908 with the double power-law hard electron energy spectrum model |
at 05:10:20 ut, the swift burst alert telescope (bat) triggered and located grb 211025a (trigger=1081113). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 162.377, +31.557 which is ra(j2000) = 10h 49m 30s dec(j2000) = +31d 33' 26" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). as is usual for an image trigger, the immediately available bat lightcurve is unclear, but there does appear to be a peak between t+30 and t+64, with a peak count rate of ~300 counts/s (15-350 kev) at ~38 s after the nominal trigger time. the xrt began observing the field at 05:12:23.2 ut, 123.3 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 162.38427, 31.51343 which is equivalent to: ra(j2000) = 10h 49m 32.22s dec(j2000) = +31d 30' 48.3" with an uncertainty of 4.1 arcseconds (radius, 90% containment). this location is 158 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 5.36e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 131 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 0.027. 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 211025a: swift detection of a burst |
grb 130427a was the brightest gamma-ray burst detected in 30 years. with an isotropic energy output of 8.5×10^{53} erg and redshift of 0.34, it combined a very high energy release with a relative proximity to earth in an unprecedented fashion. sensitive x-ray observatories such as xmm-newton and chandra have detected the afterglow of this event for a record-breaking baseline of 90 million seconds. the light curve shows a simple power-law decay over more than three decades in time. in this presentation, we explore the consequences of this result for the scenarios proposed to interpret grb 130427a, the implication of this outcome in the context of the forward shock model (beaming angle, energetics, surrounding medium), and the scientific prospects of extending grb afterglow observations for several hundreds of ms with athena. | a strong test for the forward shock model in grbs: the 90 ms follow up of the x-ray afterglow of grb 130427a. |
at 05:05:59 ut, the swift burst alert telescope (bat) triggered and located grb 231129a (trigger=1199764). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 317.536, +41.544 which is ra(j2000) = 21h 10m 09s dec(j2000) = +41d 32' 37" 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 ~3700 counts/sec (15-350 kev), at ~90 sec after the trigger. the xrt began observing the field at 05:07:51.1 ut, 112.0 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 317.54581, 41.52062 which is equivalent to: ra(j2000) = 21h 10m 10.99s dec(j2000) = +41d 31' 14.2" with an uncertainty of 4.0 arcseconds (radius, 90% containment). this location is 88 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 0.1 s image was 3.05e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 120 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. results from the list of sources generated on-board are not available at this time. no correction has been made for the large, but uncertain, extinction expected. 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 231129a: swift detection of a burst |
the provenance of swift lies with earlier discoveries of gamma ray burst (grb) phenomena, starting with the serendipitous discovery of grbs by the vela nuclear-test-ban-treaty monitoring satellites, through the first all sky grb mapping by the compton gamma-ray observatory (cgro) to the discovery of x-ray afterglows by bepposax. building on these foundations, swift has provided the astrophysics community with a new tool for studying grbs; a rapid reaction spacecraft hosting a unique combination of newly available instrument technologies able to detect, locate and follow the life cycle of bursts across their energy spectrum from gamma-ray, through x-ray, to optical/uv. the swift science team has shaped the scientific priorities for the mission and ensured access to world class observatories for rapid follow-up observations. since launch, on 2004 november 20, swift has been detecting grbs at a rate of about 100 per year. many of these have led to major breakthroughs in understanding grb phenomena and are referenced here alongside comments on some of the events that at times threatened early demise of the swift mission - happily averted through prompt action by the scientists and engineers of the mission operations team. | reflections on swift from the early years |
long-duration gamma-ray bursts (lgrbs) provide a unique way of selecting a sample of actively star-forming galaxies independent of their brightness and at practically any redshift. i will review what we know about the hosts and more immediate environments of lgrbs from two different perspectives: ultraviolet absorption-line spectroscopy of the bright early afterglow, and observations of their hosts in emission once the afterglow has faded away. | lgrb hosts in emission and in absorption |
at 03:47:02 ut, the swift burst alert telescope (bat) triggered and located grb 210725a (trigger=1061511). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 215.363, -1.177 which is ra(j2000) = 14h 21m 27s dec(j2000) = -01d 10' 36" 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 ~1800 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 03:48:53.6 ut, 110.7 seconds after the bat trigger. using promptly downlinked data we find a fading, uncatalogued x-ray source with an enhanced position: ra, dec 215.3742, -1.1934 which is equivalent to: ra(j2000) = 14h 21m 29.81s dec(j2000) = -01d 11' 36.2" 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 gives a column density in excess of the galactic value (4.09 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 3.9 (+2.81/-2.40) x 10^21 cm^-2 (90% confidence). 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 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 0.046. burst advocate for this burst is m. g. bernardini (grazia.bernardini 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 210725a: swift detection of a burst |
at 01:02:08 ut, the swift burst alert telescope (bat) triggered and located grb 210818a (trigger=1069169). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 149.131, -87.031 which is ra(j2000) = 09h 56m 32s dec(j2000) = -87d 01' 52" 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 60 sec. the peak count rate was ~28000 counts/sec (15-350 kev), at ~1 sec after the trigger. the xrt began observing the field at 01:03:06.9 ut, 59.0 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source with an enhanced position: ra, dec 148.8666, -87.0253 which is equivalent to: ra(j2000) = 09h 55m 27.99s dec(j2000) = -87d 01' 31.0" with an uncertainty of 1.9 arcseconds (radius, 90% containment). this location is 53 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 (1.74 x 10^21 cm^-2, willingale et al. 2013), with an excess column of 4.7 (+2.38/-2.11) x 10^21 cm^-2 (90% confidence). the initial flux in the 2.5 s image was 1.40e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 66 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 09:55:28.15 = 148.86729 dec(j2000) = -87:01:28.8 = -87.02467 with a 90%-confidence error radius of about 0.62 arc sec. this position is 1.9 arc sec. from the center of the xrt error circle. the estimated magnitude is 17.93 with a 1-sigma error of about 0.15. no correction has been made for the expected extinction corresponding to e(b-v) of 0.213. although this was originally reported in the gcn notices as a known source we believe that this is a grb. 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 210818a: swift detection of a burst with an optical counterpart |
at 14:46:10 ut, the swift burst alert telescope (bat) triggered and located grb 210723a (trigger=1061284). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 121.726, -32.889 which is ra(j2000) = 08h 06m 54s dec(j2000) = -32d 53' 20" 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 50 sec. the peak count rate was ~2200 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 14:47:40.4 ut, 89.6 seconds after the bat trigger. using promptly downlinked data we find a bright, fading, uncatalogued x-ray source located at ra, dec 121.72157, -32.88624 which is equivalent to: ra(j2000) = 08h 06m 53.18s dec(j2000) = -32d 53' 10.5" with an uncertainty of 7.0 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 gives a column density consistent with the galactic value of 7.70 x 10^21 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 3.04e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 99 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. although the data from this burst are consistent with a classical long grb, we note that this source is close to the galactic plane (lat = -0.34 degrees) which raises the possibility that this is a galactic transient. if further analysis determines that to be the case, we would name the object swift j0806.9-3253 . burst advocate for this burst is t. sbarrato (tullia.sbarrato 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 210723a: swift detection of a burst |
gamma-ray burst (grb) is the most violent explosion in the universe. it has strong gamma-ray emission during short timescale. for some grbs after prompt emission, x-ray flare is shown in the x-ray decay phase. the pulse of x-ray flare, similar to that of grb, has an asymmetric structure. usually the rise time of x-ray flare is less than the decay time of x-ray flare. the x-ray flare duration ranges from hundreds of seconds to thousands of seconds. in some grbs, the x-ray flare is as bright as the prompt emission. for one x-ray flare, the duration is linearly related to the peak time. the spectrum of x-ray flare is harder than that of normal x-ray afterglow. the early x-ray flare has a narrow pulse and hard spectrum, compared with the late x-ray flare. the physical mechanisms on the x-ray flare are similar to those of grb prompt emission. in the fireball model, fast shell collides with slow shell, and the internal shock is generated. the shock accelerates electrons, and the synchrotron radiation generates the x-ray flare. the fireball external shock sweeps up the interstellar medium, and the synchrotron radiation produces x-ray flare as well. in the photosphere model, x-ray flux emerges at the photospheric radius, because the jet has enormously dissipative energy near the optically thick region. the peak energy of thermal emission settles down in the x-ray band, and this makes x-ray flare. in the poynting-dominated models, grb jet has interaction with the surrounding interstellar medium, producing the instable magnetic field, which can release huge energy of the magnetic field. the x-ray flare is powered by the dissipative magnetic energy. in the case of anisotropic jet model, due to curvature effect, the anisotropic emission makes a late x-ray flare. multiple x-ray flares in one grb can be caused by the intermittent accretion of black hole after grb occurs. during the accretion, the magnetic field around the black hole can modify the accretion rate and the energy released by grb jet. | an investigation of research progress for x-ray flare in gamma-ray burst |
gamma-ray bursts (grbs), which have been observed up to redshifts z ≈ 9.5 can be good probes of the early universe and have the potential of testing cosmological models. the analysis by dainotti of grb swift afterglow lightcurves with known redshifts and definite x-ray plateau shows an anti-correlation between the <underline>rest frame</underline> time when the plateau ends (the plateau end time) and the calculated luminosity at that time (or approximately an anti-correlation between plateau duration and luminosity). we present here an update of this correlation with a larger data sample of 101 grbs with good lightcurves. since some of this correlation could result from the redshift dependences of these intrinsic parameters, namely their cosmological evolution we use the efron-petrosian method to reveal the intrinsic nature of this correlation. we find that a substantial part of the correlation is intrinsic and describe how we recover it and how this can be used to constrain physical models of the plateau emission, whose origin is still unknown. the present result could help clarifing the debated issue about the nature of the plateau emission. this result is very important also for cosmological implications, because in literature so far grb correlations are not corrected for redshift evolution and selection biases. therefore we are not aware of their intrinsic slopes and consequently how far the use of the observed correlations can influence the derived `best' cosmological settings. therefore, we conclude that any approach that involves cosmology should take into consideration only intrinsic correlations not the observed ones. | determination of intrinsic slope of the luminosity-time correlation in x-ray afterglows of grbs and its implications |
we here present the h.e.s.s. follow-up of fast radio bursts (frbs), millisecond-long, very strong radio pulses of yet unknown origin. the superb (survey for pulsars and extragalactic radio bursts) project at the parkes radio observatory is able to detect these enigmatic events almost in real-time which allows triggering follow-up observations covering the full electromagnetic spectrum. the h.e.s.s. gamma-ray observatory is taking active part in this endeavor. here we focus on data taken within hours of frb 150418, which allow us to derive the first limits on gamma-ray afterglow emission of frbs. based on the identification of the potential host galaxy of this burst we are able to discuss absorption effects due to the extragalactic background light (ebl) and derive intrinsic, energy dependent limits on the gamma-ray afterglow. | limits on the tev gamma-ray afterglow of fast radio bursts with h.e.s.s. |
at 13:00:27 ut, the swift burst alert telescope (bat) triggered and located grb 221024a (trigger=1131029). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 169.718, +33.041 which is ra(j2000) = 11h 18m 52s dec(j2000) = +33d 02' 28" 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 30 sec. the peak count rate was ~1000 counts/sec (15-350 kev), at ~3 sec after the trigger. the xrt began observing the field at 13:02:36.5 ut, 129.5 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 169.74060, 33.04207 which is equivalent to: ra(j2000) = 11h 18m 57.74s dec(j2000) = +33d 02' 31.5" with an uncertainty of 3.5 arcseconds (radius, 90% containment). this location is 68 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 (2.86 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 4 (+2.22/-1.98) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 250 seconds with the uvw2 filter starting 127 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 there is no aspect solution due to a nearby very bright star. results from the list of sources generated on-board are not available at this time. 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 221024a: swift detection of a burst |
we observed the field of grb 210704a (ursi et al., gcn 30372; berretta et al., gcn 30375; malacaria et al. gcn 30380) with the near-infrared imager (niri) mounted on the 8.1m gemini north telescope. we obtained 24x60 s imaging in j-band starting on 2021 july 10 at 06:00 ut (~5.5 days after the grb) at an average airmass of 2.0. at the location of the optical afterglow (kim et al., gcn 30384) we detect no source. preliminary calibration against nearby 2mass objects yields a 3-sigma upper limit of j>23.5 ab mag. with respect to the earlier observations reported by rastinejad et al. (gcn 30433), our data show a marginal evidence of fading. we note that nearly simultaneous swift/xrt observations still detect the x-ray afterglow at a flux level of ~4.4e-14 erg/cm2/s at 4.5 d after the burst. by using a spectral index of about 0.85, consistent with the swift/xrt spectrum (https://www.swift.ac.uk/xrt_spectra/00021454/) and the observed temporal decay with slope ~1.3, we estimate an afterglow contribution of ~23.1 ab mag to the nir emission. this suggests that the non-thermal afterglow component could have significantly contributed to the nir detection reported in rastinejad et al. (gcn 30433). we thank the gemini staff for scheduling and executing these observations. | grb210704a: gemini near-infrared upper limits |
swift-xrt has performed follow-up observations of the second optical afterglow candidate observed by meerlicht (de wet et al. gcn circ. 32460) of the fermi/gbm detected burst grb 220810a (fermi gbm team, gcn 32455), collecting 4.9 ks of photon counting (pc) mode data between t0+156.3 ks and t0+180.2 ks. no x-ray sources have been detected consistent with being within 9.9 arcsec of the meerlicht optical afterglow candidate position. the 3-sigma upper limit in the field is 0.003 ct s^-1, corresponding to a 0.3-10 kev observed flux of 1.1e-13 erg cm^-2 s^-1 (assuming a typical grb spectrum). 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/00021510. this circular is an official product of the swift-xrt team. | grb 220810a: swift-xrt observations |
at 16:09:14 ut, the swift burst alert telescope (bat) triggered and located grb 220706a (trigger=1114937). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 0.587, -16.391 which is ra(j2000) = 00h 02m 21s dec(j2000) = -16d 23' 28" 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 50 sec. the peak count rate was ~1400 counts/sec (15-350 kev), at ~1 sec after the trigger. the xrt began observing the field at 16:10:57.0 ut, 102.8 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 0.60368, -16.41065 which is equivalent to: ra(j2000) = 00h 02m 24.88s dec(j2000) = -16d 24' 38.3" with an uncertainty of 3.5 arcseconds (radius, 90% containment). this location is 91 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 (2.40 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 6.6 (+4.12/-3.33) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 107 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 0.025. 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 220706a: swift detection of a burst |
grb 170817a, the first short gamma-ray burst (sgrb) to be detected after the gravitational wave signal from a binary neutron star (bns) merger, proved that such merger events are able to power relativistic jets and provided unprecedented insights into the associated electromagnetic (em) emission at all wavelengths. the origin of sgrb jets remains however a matter of debate, and many theoretical and phenomenological models, combining observational data with results of numerical calculations, are currently under development with the aim of unveiling it. one key aspect under investigation is how the ultimate jet properties are shaped by the interaction of the initial outflow with the surrounding post-merger environment. in this talk, i will present results of numerical simulations in which we modelled, for the first time, the three-dimensional (magneto-)hydrodynamic evolution of an sgrb jet propagating through the post-merger environment of a fully general-relativistic (gr) magnetized bns merger simulation. our results shed light on the role of magnetic fields in the jet propagation and open the way for a systematic investigation of how the physical conditions at the time of jet launching affect the ultimate jet properties and thus the prompt and afterglow sgrb signals. | short gamma-ray burst jet propagation through self-consistent post-merger environments |
the afterglow emission of gamma-ray bursts (grbs) often shows a nearly constant flux evolution ("plateau") lasting ~ hours after the prompt emission. plateaus are typically observed in x-rays but in a fraction of events they are also observed in the optical bands. the origin of the plateau is still unknown and several interpretations have been proposed. in this work we investigate the spectro-temporal properties of plateaus observed in x-rays with well monitored optical counterparts for a sample of 29 grbs, aiming to disentangle different interpretations. we identify a "golden" sample of 15 grbs, and for 13 of which we find evidence of a plateau also in optical, with r-band flux densities consistent with a broad-band synchrotron spectrum in the framework of the standard external-shock model. considering the full sample, 26 grbs (~ 90%) have the optical and x-ray flux densities consistent with the same synchrotron spectrum during the x-ray plateau temporal window. we discuss our findings in the context of two possible interpretations of the plateau origin. as a general conclusion, our broad-band analysis proved to be a powerful diagnostic to identify grbs with plateau features consistent with a standard synchrotron scenario and those for which a more complex scenario should be considered in their interpretation. | on the origin of afterglow "plateaus" in gamma-ray bursts |
swift-xrt has performed further follow-up observations of the swift/bat-guano-detected burst grb 210827a (james delaunay et al. gcn circ. 30732), collecting a total of 12.2 ks of photon counting (pc) mode data between t0+44.4 ks and t0+257.2 ks. the uncatalogued candidate x-ray source (source 3) reported in gropp et al. (gcn circ. 30734) faded to a count-rate of 3e-3 ct s^-1, thus suggesting it as the likely x-ray afterglow of grb 210827a. the light curve can be described with a single power-law with a decay index alpha = 1.0 (+0.5, -0.4). the results of the xrt-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/00021461 <https://www.swift.ac.uk/xrt_products/00021461> this circular is an official product of the swift-xrt team. | grb 210827a: further swift-xrt observations |
we report the discovery of the fast and red optical transient ztf22aaajecp/at2022cmc with the zwicky transient facility (ztf, bellm et al. 2019, graham et al. 2019) at coordinates: ra = 13:34:43.20 (203.6800149d) dec = +33:13:00.44 (33.2167887d) ztf22aaajecp was first detected on 2022-02-11 10:42 ut at r=20.73 +- 0.3 mag. the last ztf upper limit before the first detection was measured on 2022-01-21 09:54 ut. ztf22aaajecp increased its luminosity to r=19.04 +- 0.16 mag in 23.2 hours, then it faded by 0.8 mag in the following 48 hours. the latest detection of ztf22aaajecp occurred on 2022-02-14 09:40 ut, r=19.84 +- 0.19 mag. the color of ztf22aaajecp appears to be red, with g-r~0.25 mag and g-i~0.5 mag at the observed peak on 2022-02-12. the galactic extinction on the line of sight is small, with e(b-v)=0.01 mag (planck collaboration et al., 2014). the source is located at a high galactic latitude of b=78.85 deg. ztf22aaajecp does not have any cataloged underlying source in deep legacy survey dr9 images. the fast evolution and red color suggest that ztf22aaajecp could be a gamma-ray burst afterglow, but a spectroscopic confirmation is required to determine the nature of the transient. ztf22aaajecp is spatially and temporally consistent with the fermi-gbm short grb 220211a (gbm trigger 666234473); however, it is located several degrees outside the ipn localization region for this event (ridnaia et al. 2022; gcn 31584). follow-up observations are strongly encouraged. ztf22aaajecp was discovered by the ''ztf realtime search and triggering'' project (ztfrest; andreoni & coughlin et al., 2021) within the ztf collaboration. based on observations obtained with the samuel oschin telescope 48-inch and the 60-inch telescope at the palomar observatory as part of the zwicky transient facility project. ztf is supported by the national science foundation under grant no. ast-2034437 and a collaboration including caltech, ipac, the weizmann institute for science, the oskar klein center at stockholm university, the university of maryland, deutsches elektronen-synchrotron and humboldt university, the tango consortium of taiwan, the university of wisconsin at milwaukee, trinity college dublin, lawrence livermore national laboratories, and in2p3, france. operations are conducted by coo, ipac, and uw. | ztf22aaajecp/at2022cmc: zwicky transient facility discovery of a fast and red optical transient |
recently, ground-based imaging atmospheric cherenkov telescopes, such as magic and h.e.s.s., have reported the detection of very-high-energy (vhe) gamma-rays from four gamma-ray bursts (grb 180720b, 190114c, 190829a, 201216c). one of them, grb 190829a, was triggered by the swift satellite, and about 20000 s after the burst onset the vhe gamma-ray emission was detected by h.e.s.s. with ∼ 20 sigma significance. this event had more unusual features than the other vhe gamma-ray events. 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 2000 s. we propose an off-axis jet model 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 300-500 and the initial jet opening half-angle of 0.01-0.02 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. our model parameters determined by x-ray, optical and radio afterglows may roughly explain observed vhe gamma-ray flux. | on theoretical interpretation of broad-band afterglows of a very-high-energy grb 190829a |
at 10:31:52 ut, the swift burst alert telescope (bat) triggered and located grb 230427a (trigger=1165948). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 153.324, +48.180 which is ra(j2000) = 10h 13m 18s dec(j2000) = +48d 10' 48" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). no bat light-curve is available at this time. the xrt began observing the field at 10:33:25.9 ut, 94.0 seconds after the bat trigger. using promptly downlinked data we find a fading, uncatalogued x-ray source with an enhanced position: ra, dec 153.31199, 48.20404 which is equivalent to: ra(j2000) = 10h 13m 14.88s dec(j2000) = +48d 12' 14.6" with an uncertainty of 1.9 arcseconds (radius, 90% containment). this location is 91 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 (8.35 x 10^19 cm^-2, willingale et al. 2013), with an excess column of 3.5 (+2.81/-2.63) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 98 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 10:13:15.05 = 153.31270 dec(j2000) = +48:12:14.4 = 48.20400 with a 90%-confidence error radius of about 0.74 arc sec. this position is 1.4 arc sec. from the center of the xrt error circle. the estimated magnitude is 20.31 with a 1-sigma error of about 0.20. no correction has been made for the expected extinction corresponding to e(b-v) of 0.007. burst advocate for this burst is e. troja (nora.gsfc 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 230427a: swift detection of a burst with an optical counterpart |
in this thesis, we present three projects on open questions in the gammaray burst (grb) field. in the first project, we used x-ray and optical observations to determine the amount of amplification of the ism magnetic field needed to explain the grb afterglow observations. we determined that mild amplification is required, at a level stronger than shock-compression but weaker than predicted by the weibel mechanism. in the second project, we present a monte carlo code we wrote from scratch to perform realistic simulations of the photospheric process, one of the mechanisms considered to explain the grb gamma-ray emission. we determined that photospheric emission can explain the grb gamma-ray spectrum above the peak-energy if the photons are taken to have a temperature much smaller than the electron temperature and if the interactions between photons and electrons take place at a large optical depth. in the third project, we used multi-wavelength observations to constrain the x-ray flare radiation mechanism. we determined that synchrotron from a poynting jet and the photospheric process are the best candidates to explain the x-ray flare observations. | towards understanding magnetic field generation in relativistic shocks with grb afterglow observations and the grb radiation mechanism with photospheric simulations and the x-ray flare radiation mechanism |
the follow-up of $\gamma$-ray bursts (grbs) by the x-ray telescope (xrt, 0.3-10 kev) on board the neil gehrels swift observatory led to the discovery of a shallow decay phase (the so-called plateau) of the x-ray emission in a good fraction of grbs. this unexpected temporal behaviour does not fit the standard grb afterglow expectation. thus, in the last years, many models emerged, that invoke energy injection into the external shock, requiring long-lasting activity of the central engine of grbs. we discuss a new alternative, comprehensive model: the plateau phase originates from the high latitude emission (i.e., the radiation observed from larger angles relative to the line of sight, after the prompt emission from a curved surface is switched off) when the jet exhibits bulk motion and intensity structure. this model enables us to reproduce not only the temporal behaviour of the x-ray light curves, but also the diversity of joint optical-to-x-ray emission. | x-ray plateaus in \\gamma-ray bursts explained by structured jets |
the prompt emission of the long, smooth, and single-pulsed gamma-ray burst, grb 141028a, is analyzed under the guise of an external shock model. first, we fit the γ-ray spectrum with a two-component photon model, namely synchrotron+blackbody, and then fit the recovered evolution of the synchrotron ν f_{ν} peak to an analytic model derived considering the emission of a relativistic blast-wave expanding into an external medium. the prediction of the model for the ν f_{ν} peak evolution matches well with the observations. we observe the blast-wave transitioning into the deceleration phase. further we assume the expansion of the magnetic field deduced from the observations. this allows us to recover within an order of magnitude the flux density at the ν f_{ν} peak, which is remarkable considering the simplicity of the analytic model. under this scenario we argue that the distinction between prompt and afterglow emission is superfluous as both early and late time emission emanate from the same source. while the external shock model is clearly not a universal solution, this analysis opens the possibility that at least some fraction of grbs can be explained with an external shock origin of their prompt phase. | an external shock origin of grb 141028a |
dark gamma-ray bursts (grbs) -- where the optical emission is apparently suppressed -- can only be reliably localized by their x-ray afterglows. here we propose to continue a survey using the sensitivity and point spread function of chandra to precisely pinpoint the grb locations, and hst to locate and study the host galaxies. our results to date are suggestive of most dark grbs originating in more luminous galaxies than "bright" grbs. our new observations will increase the statistical certainty of this result, while simultaneously allowing us to more precisely identify the minority of dark grbs which most likely originate from the highest redshifts. | a chandra/hst survey of dark gamma-ray bursts |
the electromagnetic counterpart of the binary neutron-star merger gw 170817, connected with the short grb 170817a, has been monitored from early to very late times at all wavelengths. multi-band observations demonstrated the existence of the kilonova emission associated with the merger of a binary neutron-star system, as expected from several theoretical models. we discuss the temporal evolution of the associated gamma-ray burst afterglow emission in the x-rays and radio bands, detected at later times. these observations seem to finally support a flattening/decaying behaviour, favouring the structured jet interpretation, over the isotropic emission scenario, for the origin of the electromagnetic signal. | the evolution of the x-ray and radio emission of gw 170817/grb 170817a |
at 13:58:04 ut, the swift burst alert telescope (bat) triggered and located grb 220714b (trigger=1116221). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 47.072, -19.334 which is ra(j2000) = 03h 08m 17s dec(j2000) = -19d 20' 02" 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 ~5500 counts/sec (15-350 kev), at ~13 sec after the trigger. the xrt began observing the field at 13:59:20.9 ut, 76.4 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 47.0803, -19.3269 which is equivalent to: ra(j2000) = 03h 08m 19.27s dec(j2000) = -19d 19' 36.8" with an uncertainty of 5.2 arcseconds (radius, 90% containment). this location is 38 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 1.70e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 56 seconds with the white filter starting 121 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 position. 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 0.032. 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 220714b: swift detection of a burst |
following the remarkable neutron star binary merger known as gw170817, much research has been conducted to uncover its nature and investigate whether its nearby location presents an opportunity to unveil similar events. gw170817 was accompanied by a kilonova, plus a delayed radio afterglow related to an off-axis jet that differs from those previously observed in gamma-ray bursts (grbs). it has thus been suggested that such delayed emission may have been missed in previously-known grbs. in this context, i will present the results of an analysis aimed at determining whether previously-detected grbs, lacking accurate localization and an early afterglow detection, could have originated from events similar to gw170817. specifically, i will discuss the results of a late-time radio follow-up campaign of a subset of short grbs in the swift/bat sample. the goal of this campaign, carried out with the jansky very large array (vla), is to determine whether any of the grbs in our sample is associated with delayed radio emission. i will show how such late-time emission, using its time variability and spectral energy distribution, can be used to constrain whether nearby ejecta similar to gw170817 were produced in any of the considered grbs. | a search for gw170817-like nearby grbs in the swift/bat sample |
swift-xrt has performed follow-up observations of the fermi/lat-detected burst grb 220527a (bissaldi et al. gcn circ. 32131), collecting 1.7 ks of photon counting (pc) mode data between t0+30.1 ks and t0+31.9 ks. two uncatalogued x-ray sources are detected, of which one ("source 2") is above the rass 3-sigma upper limit at this position, and is therefore likely the grb afterglow. using 1733 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 = 323.52805, -14.97183 which is equivalent to: ra (j2000): 21h 34m 06.73s dec(j2000): 14d 58' 18.6" with an uncertainty of 2.6 arcsec (radius, 90% confidence). this position is 4.9 arcmin from the fermi/lat position. the light curve is consistent with a constant source of mean count rate 3.9e-01 ct/sec. a power-law fit gives an index of 0.6 (+2.5, -1.1). a spectrum formed from the pc mode data can be fitted with an absorbed power-law with a photon spectral index of 1.83 (+0.21, -0.20). the best-fitting absorption column is 9.8 (+6.1, -3.5) x 10^20 cm^-2, consistent with the galactic value of 6.2 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 3.6 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. a summary of the pc-mode spectrum is thus: total column: 9.8 (+6.1, -3.5) x 10^20 cm^-2 galactic foreground: 6.2 x 10^20 cm^-2 excess significance: <1.6 sigma photon index: 1.83 (+0.21, -0.20) the results of the xrt-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021503. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021503. this circular is an official product of the swift-xrt team. | grb 220527a: swift-xrt afterglow detection |
on august 17, 2017, ligo/virgo detected the first gravitational waves from merging neutron stars. this event, known as gw170817 was accompanied by observations all over the electromagnetic spectrum. the peculiar gamma-ray burst that followed the merger in gw170817, is unlike any gamma-ray burst observed before. in order to explain the afterglow observations, there is a need for the jet launched after the merger to have structure, which is a natural consequence of the interaction of the jet with the ambient medium. in this talk, i will show special relativistic simulations of the interaction of the jet with several outflows launched during the merger and compare the simulations to the observation. i will then use the results in order to constrain key properties of the merger, such as the delay time between the merger and the collapse to a black hole. | binary neutron star mergers: the fate of the merger remnant in gw170817 and its imprint on the jet structure |
gamma ray bursts (grbs) can be used as a powerful tool to study galactic environments at different epochs of the universe’s evolution, thanks to their bright afterglow emission ranging from x-rays to optical and radio wavebands. important aspect of the environment is dust, which plays a central role in the astrophysical processes of interstellar medium and in the formation of stars. grbs can be a unique probe of dust at cosmological distances, where its origin and properties are still poorly known.by using a sample of grb afterglow spectra observed with the vlt/x-shooter spectrograph we studied the rest-frame extinction in grb lines-of-sight by modelling the broadband near-infrared to x-ray afterglow spectral energy distributions. we will present our results on the rest-frame extinction of our sample, and illustrate that the spectroscopic data, thanks to a combination of excellent resolution and coverage of the blue part of the spectral energy distributions, are more successful than photometric measurements in constraining the extinction curves and therefore the dust properties in grb hosts. | extinction curves of grb environment with the x-shooter spectrograph |
current time-domain wide-field sky surveys generally operate with few-degree-sized fields and take many individual images to cover large sky areas each night. we present the design and project status of the evryscope ("wide-seer"), which takes a different approach: using an array of small telescopes to form a single wide-field-of-view pointed at every part of the accessible sky simultaneously and continuously. the evryscope is a gigapixel-scale imager with a 10,000 sq. deg. field of view and has 10% of the etendue of lsst. each 2-minute exposure will reach v=16.4; 3-mmag-level scinitillation-limited photometry will be obtained on bright stars every 15 minutes. each year the evryscope will generate 70,000+ photometric datapoints on tens of millions of stars. the system will search for transiting exoplanets around bright stars, m-dwarfs and white dwarfs, as well as detecting microlensing events, nearby supernovae, and gamma-ray burst afterglows. all data will be recorded long-term, allowing post-facto follow-up of interesting events. the evryscope is currently under construction and is planned for deployment in 2015. we present the current project status, including an update on the evryscope prototype telescopes we have been operating for the last three years in the canadian high arctic. | the evryscope: the first full-sky gigapixel-scale telescope |
gamma-ray burst (grb) afterglows shine, during a brief period of time as the most luminous objects that can be detected in the universe. they have been observed at almost any redshift, from our nearby environment (the nearest one, at z = 0.08) to the very distant universe (the current record holder at z = 9.4). their optical spectra are well reproduced by a clean, simple power law, making them ideal light houses to probe the interstellar medium of their host galaxies at any redshift. we have used the largest sample of grb afterglow spectra collected to date to perform a statistical study of the interstellar medium in their host galaxies. by analysing the distribution of equivalent widths of the most prominent absorption features we evaluate the different types of environments that host grbs and study their diversity. | statistical study of the ism of grb hosts |
in the gamma ray burst afterglow model, a relativistic shell forms which is unstable to the rayleigh-taylor instability during the formation of a relativistic blastwave. this instability is likely observable, and understanding the resulting turbulence have motivated many previous studies into the rayleigh-taylor instability in the context of a relativistic fireball. we study the rayleigh-taylor instability in a relativistic gamma ray burst outflow with and without magnetic fields. we also examine the growth of the magnetic fields with different lorentz factors. the simulations are performed using a wavelet based adaptive mesh refinement method. | examing the rayleigh-taylor instability in grb outflow using wavelets |
we discuss the lack of a clear jet-break in the optical and x-ray afterglow light curve of grb 130427a, which suggests that a very large isotropic energy is emitted in this burst. | to beam or not to beam. . . |
while the dominant radiation mechanism gamma-ray bursts (grbs) remains a question of debate, synchrotron emission is one of the foremost candidates to describe the multi-wavelength afterglow observations. as such, it is expected that grbs should present some degree of polarization across their evolution - presenting a feasible means of probing these bursts' energetic and angular properties. although obtaining polarization data is difficult due to the inherent complexities regarding grb observations, advances are being made, and theoretical modeling of synchrotron polarization is now more relevant than ever. in this manuscript, we present the polarization for a fiduciary model where the synchrotron forward-shock emission evolving in the radiative-adiabatic regime is described by a radially stratified off-axis outflow. this is parameterized with a power-law velocity distribution and decelerated in a constant-density and wind-like external environment. we apply this theoretical polarization model for selected bursts presenting evidence of off-axis afterglow emission, including the nearest orphan grb candidates observed by the neil gehrels swift observatory and a few gravitational wave (gws) events that could generate electromagnetic emission. in the case of grb 170817a, we require the available polarimetric upper limits in radio wavelengths to constrain its magnetic field geometry. | polarization from a radially stratified off-axis grb outflow |
the simultaneous detection of gravitational waves by the ligo and virgo detectors from a binary neutron star (bns) merge, gw 170817, is the first gravitational wave event that has electromagnetic (em) follow-up observations, from gamma-rays to millimeter wavelengths. the data from these em counterparts lead to the idea that the gw 170817 might be the first off-axis afterglow observed from a short gamma-ray burst (sgrb), and they would provide the first direct observational evidence for the launching of relativistic jets in bns mergers. the properties of the jets, as well as their interaction with the environment, can be studied at the microscopic level by using particle-in-cell (pic) numerical simulations. we study the evolution of relativistic plasma jets containing helical magnetic fields and examine how these helical magnetic fields affect (i) kinetic instabilities (such as the weibel instability, the kinetic kelvin-helmholtz instability, and the mushroom instability) and (ii) magnetic reconnection in the jets. we also calculate synthetic spectra and spectral evolution for the off-axis radiation emitted by the particles accelerated in such sgrb jets and compare them with observations. nevertheless, simulations using very large systems are required in order to thoroughly follow the evolution of global jets containing helical magnetic fields. | synthetic spectra for an off-axis afterglow from a short gamma-ray burst |
here, we present the grb 141220a optical photometry corresponding to the liverpool telescope (lt) ringo3 bv,r,i bands, skycam-z r-equivalent band, and io:o r band. a bright optical afterglow of 14.84+/-0.17 mag was detected 86s after bat trigger at the grb 141220a location by the 0.2-m skycam-z telescope, attached to the 2-m lt. at 129.5s post-burst, the lt reacted automatically to swift alert with the three-band optical polarimeter and imager ringo3 and started observations. lt observations consisted of 3x10min epochs of ringo3 instrument, followed by 6x10s frames with the r band of the optical wide field camera (io:o) and 7x10min more with ringo3. the tabulated data includes the bandpass name, the mean observing time corrected by t0 (swift trigger time), the length of the observing window and the grb magnitudes and flux density with their uncertainties. note that the skycam-z white-band photometry has been standarized in the r sdss band. the magnitudes and the flux density are corrected by galactic extinction (reddening e(b-v)=0.0128+/-0.0005; schlegel et al., 1998apj...500..525s), but not by host galactic extinction (e(b-v)=0.24+/-0.06). (1 data file). | vizier online data catalog: grb 141220a light curves (jordana-mitjans+, 2021) |
at 10:29:51 ut, the swift burst alert telescope (bat) triggered and located grb 230205a (trigger=1152764). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 202.072d, +46.684d which is ra(j2000) = 13h 28m 17s dec(j2000) = +46d 41' 01" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). due to a telemetry gap, the bat light curve before t+8s is not immediately available, and after that time shows no obvious variability. the bat rate trigger was on a 3 s timescale, consistent with the lack of variation at later times. the xrt began observing the field at 10:31:40.0 ut, 108.8 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 202.07147, 46.72613 which is equivalent to: ra(j2000) = 13h 28m 17.15s dec(j2000) = +46d 43' 34.1" with an uncertainty of 1.9 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. 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 (2.09 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 1.2 (+0.71/-0.56) x 10^22 cm^-2 (90% confidence). 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 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 0.036. 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 230205a: swift detection of a burst |
swift-xrt has performed follow-up observations of the ipn-detected burst grb 230906a (kozyrev et al., gcn circ 34637), collecting 4.7 ks of photon counting (pc) mode data between t0+93.0 ks and t0+106.0 ks. one uncatalogued x-ray source has been detected, 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): 79.7533 = 05:19:0.79 dec (j2000.0): -47.8930 = -47:53:34.9 error: 6.4 arcsec (radius, 90% conf.) count-rate: (1.73 [+0.88, -0.67])e-3 ct s^-1 distance: 23 arcsec from ipn position. 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/00021621. this circular is an official product of the swift-xrt team. | grb 230906a: swift-xrt observations |
we observed the field of ztf23aaoohpy/at2023lcr (swain et al., gcn 34022, gompertz et al., gcn34023, kumar et al., gcn34025)using the t193cm and t120cm telescopes at observatoire de haute-provence (france) respectively equipped with the mistral spectro-imager and the t120 ccd camera. a total of 8 exposures were obtained in the imaging mode of mistral in the r-band filter (1x360s +7x600s). observations were made from 2023-06-19 21:13:47.60 ut to 2023-06-19t22:37:40.86 ut (mid time ~1.85d after the t_goto = 2023-06-18 01:27:41 (gompertz et al., gcn34023)). a total of 16 exposures were also obtained with the t120 ccd camera in the r-band filter (1x300s +8x450s, mid time ~ t_goto+1.83d) and v-band (7x600s, mid time ~ t_goto+1.88d). in the coadded images, we measured the following magnitudes: ---------------------------------------------------------------------- jd (mid) | telescope | filter | exposure (s) | magnitude (ab) | ---------------------------------------------------------------------- 2460115.3875 | ohp-t120 | r | 3900 | 20.70 +/- 0.12 | 2460115.413706 | ohp-t193/mistral | r' | 4560 | 20.84 +/- 0.04 | 2460115.440972 | ohp-t120 | v | 4200 | 20.85 +/- 0.07 | ---------------------------------------------------------------------- the photometric calibration was performed using nearby stars from the ps1 catalog and the magnitudes are not corrected for galactic extinction. our measurements confirm that the source is fading at a mag rate ~ 0.9 mag/day compared to the last r magnitude reported by ztf (swain et al., gcn 34022). the red color of this transient g-r ~ 0.3 and its confirmed fast-fading evolution are consistent with a gamma-ray burst afterglow emission. we strongly encourage spectroscopic follow-up of this source in order to identify its astrophysical origin. additional i-band follow-up observation will be performed at ohp this night. we acknowledge the excellent support from observatoire de haute-provence, in particular yoann degot longhi for the mistral observations, gavin coleman the observer using the t193/sophie instrument who allowed us to perform these too observations as well as pascal gallais, antoine claret and matthias tornay for the t120 observations. | ztf23aaoohpy/at2023lcr: ohp/t193 and ohp/t120 optical follow-up observations |
swift-xrt has performed follow-up observations of the swift/bat-guano-detected burst grb 221231a, collecting 5.0 ks of photon counting (pc) mode data between t0+32.4 ks and t0+44.3 ks. five 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. sources 2 and 5 are inside the error box of swift/bat-guano, but source 5 is associated with a known source. details of these sources are given below: source 1: ra (j2000.0): 336.3458 = 22:25:22.98 dec (j2000.0): +25.1723 = +25:10:20.3 error: 6.5 arcsec (radius, 90% conf.) count-rate: (9.1 [+7.3, -5.4])e-4 ct s^-1 distance: 303 arcsec from swift/bat-guano position. source 2: ra (j2000.0): 336.2560 = 22:25:1.44 dec (j2000.0): +25.1298 = +25:07:47.2 error: 3.1 arcsec (radius, 90% conf. [enhanced position]) count-rate: 0.0107 [+0.0022, -0.0020] ct s^-1 distance: 34 arcsec from swift/bat-guano position. flux: (5.44 [+1.13, -1.00])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 3: ra (j2000.0): 336.2019 = 22:24:48.46 dec (j2000.0): +25.0298 = +25:01:47.3 error: 5.4 arcsec (radius, 90% conf.) count-rate: (1.87 [+0.97, -0.73])e-3 ct s^-1 distance: 435 arcsec from swift/bat-guano position. flux: (7.8 [+4.0, -3.1])e-14 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 4: ra (j2000.0): 336.2146 = 22:24:51.50 dec (j2000.0): +25.2635 = +25:15:48.7 error: 8.9 arcsec (radius, 90% conf.) count-rate: (1.48 [+0.87, -0.64])e-3 ct s^-1 distance: 474 arcsec from swift/bat-guano position. flux: (2.7 [+1.6, -1.2])e-14 erg cm^-2 s^-1 (observed, 0.3-10 kev) source 5: ra (j2000.0): 336.2452 = 22:24:58.84 dec (j2000.0): +25.1872 = +25:11:14.1 error: 5.7 arcsec (radius, 90% conf.) count-rate: (5.6 [+1.8, -1.5])e-3 ct s^-1 distance: 182 arcsec from swift/bat-guano position. flux: (1.12 [+0.37, -0.30])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/00021534. this circular is an official product of the swift-xrt team. | grb 221231a: swift-xrt observations |
the origin of prompt emission in $\gamma$-ray bursts (grbs) is highly debated topic. the observed spectra are supposed to play a crucial role in constraining the location of the emitting region, the strength of the magnetic field and the distribution of the accelerated particles. the apparent inconsistency of the prompt emission spectra with the synchrotron radiation scenario has resulted in considering more complex models. the inclusion of the soft x-ray data (down to 0.5 kev) in grb spectra have led to the discovery of low-energy breaks in their spectra. more importantly, the distribution of spectral slopes has been shifted towards the prediction of the synchrotron radiation scenario if the break is associated with the synchrotron cooling frequency. we discuss the recent study that systematically extend the range of investigation down to the optical domain. it was shown that the optical-to-gamma-rays spectra are consistent with the synchrotron model. in addition, widely used empirical model made of thermal and non-thermal components has been tested. we conclude that most of the spectra are consistent with the synchrotron scenario while the two-component model faces difficulties to account for the optical radiation in presence/absence of the contaminating afterglow emission. we comment on the parameter space of grb emitting region derived from the best fit parameters of the synchrotron model. in a basic one-shot particle acceleration model it corresponds to the quite contrived solutions for the magnetic field strength ($\sim$ 10 g) and for the radius of the emitting region ($r_\gamma \ge 10^{16}$ cm). possible modifications of the basic model would be necessary to have a fully consistent picture. | early optical emission in support of synchrotron radiation in \\gamma-ray bursts |
at 13:35:08 ut, the swift burst alert telescope (bat) triggered and located grb 170526a (trigger=754549). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 4.708, +1.240 which is ra(j2000) = 00h 18m 50s dec(j2000) = +01d 14' 22" 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 8 sec. the peak count rate was ~1200 counts/sec (15-350 kev), at ~5 sec after the trigger. the xrt began observing the field at 13:37:13.2 ut, 124.3 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 4.7074, 1.2773 which is equivalent to: ra(j2000) = 00h 18m 49.79s dec(j2000) = +01d 16' 38.1" with an uncertainty of 4.9 arcseconds (radius, 90% containment). this location is 134 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 3.16 x 10^20 cm^-2 (willingale et al. 2013). uvot took a finding chart exposure of 150 seconds with the white filter starting 127 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 0.03. burst advocate for this burst is b. sbarufatti (boris.sbarufatti 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/too.html.) | grb 170526a: swift detection of a burst |
afterglows of gamma-ray bursts often show flares, plateaus, and sudden intensity drops: these temporal features are difficult to explain as coming from the forward shock. we calculate radiative properties of early grb afterglows with the dominant contribution from the reverse shock (rs) propagating in an ultra-relativistic (pulsar-like) wind produced by the long-lasting central engine. rs emission occurs in the fast cooling regime -- this ensures high radiative efficiency and allows fast intensity variations. we demonstrate that: (i) mild wind power, of the order of $\sim 10^{46}$ erg s$^{-1}$, can reproduce the afterglows' plateau phase; (ii) termination of the wind can produce sudden steep decays; (iii) mild variations in the wind luminosity can produce short-duration afterglow flares. | wind-powered afterglows of gamma-ray bursts: flares, plateaus and steep decays |
swift has performed further observations of the field of the fermi/lat-detected burst grb 170522a (arimoto et al., gcn circ. 21127). an additional 3.5 ks of data were collected between 987 ks and 999 ks after the fermi trigger. source 1, initially reported by mingo et al. (gcn circ. 21133), is no longer detected to a 3-sigma upper limit of 4.3e-3 ct s^-1. we therefore conclude that this source is likely the x-ray afterglow of grb 170522a. this circular is an official product of the swift-xrt team. | grb 170522a: confirmation of the x-ray afterglow |
international scientific optical network (ison) is one of largest observing networks specializing in space objects. the main goals of ison are the investigation of space debris, studying near earth asteroids (nea) and observing gamma-ray-bursts (grb) afterglows. ison is continuously growing and currently has 35 observation facilities in 15 countries, with 80 telescopes of different apertures (from 12.5 cm to 2.6 m)(see fig. 1). 8.4 millions of measurements in 1.26 millions of tracks for about 4000 space debris objects were collected by ison in 2014 and used for analysis. currently 3 observatories collaborate with ison in the western hemisphere: tarija in bolivia, cosala in mexico and mayhill in usa. | international scientific optical network (ison) in latin america |
the swift-uvot and xrt began settled observations of the field of grb 170524b 120 ks after the bat trigger (barthelmy et al., gcn circ. 21142). a fading source consistent with the xrt position is detected in the uvot exposures. swift-xrt performed follow-up observations of the swift/bat-detected burst grb 170524b (barthelmy et al. gcn circ.21142), collecting an additional 3ks (5.1 total) of photon counting (pc) mode data. one uncatalogued x-ray source has been detected consistent with being within 296 arcsec of the swift/bat position. there is also evidence of fading, which is confirmed with uvot analysis. xrt light curve can be modeled with a power-law decay with a decay index alpha = 1.3 the preliminary uvot position is: ra (j2000) = 06:03:28.49 = 90.86872 (deg.) dec (j2000) = -17:04:58.7 = -17.08297 (deg.) with an estimated uncertainty of 0.4 arc sec. (radius, 90% confidence). preliminary detections using the uvot photometric system (breeveld et al. 2011, aip conf. proc. 1358, 373) for the early exposures are: filter t_start(s) t_stop(s) exp(s) mag white 120431 126833 1297 19.89+-0.08 white 274703 286595 2027 21.11+-0.23 the magnitudes in the table are not corrected for the galactic extinction due to the reddening of e(b-v) = 0.19 in the direction of the burst. the decay inferred from the uvot white data suggests a slope of approximately -1.3. this circular is an official product of the swift team. | grb 170524b: swift-uvot/xrt confirmation of afterglow |
we present a method to estimate the jet opening angles of long duration gamma-ray bursts (grbs) using the prompt gamma-ray energetics and an inversion of the ghirlanda relation, which is a correlation between the time-integrated peak energy of the grb prompt spectrum and the collimation-corrected energy in gamma-rays. the derived jet opening angles using this method and detailed assumptions match well with the corresponding inferred jet opening angles obtained when a break in the afterglow is observed. furthermore, using a model of the predicted long grb redshift probability distribution observable by the fermi gamma-ray burst monitor (gbm), we estimate the probability distributions for the jet opening angle and rest-frame energetics for a large sample of gbm grbs for which the redshifts have not been observed. previous studies have only used a handful of grbs to estimate these properties due to the paucity of observed afterglow jet breaks, spectroscopic redshifts, and comprehensive prompt gamma-ray observations, and we potentially expand the number of grbs that can be used in this analysis by more than an order of magnitude. in this analysis, we also present an inferred distribution of jet breaks which indicates that a large fraction of jet breaks are not observable with current instrumentation and observing strategies. we present simple parameterizations for the jet angle, energetics, and jet break distributions so that they may be used in future studies. (1 data file). | vizier online data catalog: jet angles and gamma-ray energetics estimations (goldstein+, 2016) |
with the discovery of the electromagnetic counterpart of the gravitational wave source gw170817 the multi-messenger era is started. the identification of an electromagnetic counterpart is crucial to understand the nature of the detected gravitational wave sources and to maximize the scientific return of their detections. the role of the instrument theseus/irt will be crucial in this field, in particular in localizing afterglows of gamma-ray bursts within few minutes from the trigger and in identifying optical/nir isotropic emissions such as kilonovae. | infrared emission from gravitational wave sources with theseus/irt. |
the hosts of long gamma-ray bursts (grbs) are places of intense star-formation, which, at low redshift, are primarily low-mass dwarf starburst galaxies. spatially resolved studies of these galaxies are still sparse, even more so at high spectral resolution where we can probe gas kinematics, in- and outflows and differences in abundance between different components. here we present the first high resolution ifu sample of six low redshift grb hosts, all dwarf starbursts. all galaxies in our sample show evidence for excess emission or broad emission components, with velocities of 100-200 km s-1. for grb 030329, outflowing gas had also been observed in absorption in spectra of the grb afterglow. the high velocity emission is usually blue shifted, connected to the brightest star-forming regions and more metal rich than the narrow component associated with the emission of the general host ism. this gives strong indications that the excess emission/broad component is indeed associated to a starburst wind as observed in many field star-burst galaxies and a sign for the intense ongoing star-formation in those galaxies. | dwarf galaxies as hosts of stellar explosions: gas kinematics and abundances in 3d |
the laser interferometer gravitational-wave observatory (ligo) and virgo observatory detect gravitational wave (gw) emission from neutron star mergers. when ligo/virgo detect a neutron star merger, fully characterizing the event is challenging due to fairly poor localizations of ~10-100's of square degrees, and relies on the detection of an electromagnetic signal. to potentially improve searches following gw events, we present a study to characterize the behavior of radio off-axis afterglows from neutron star mergers. assuming that the properties of neutron star mergers are drawn from the same distributions as those of short gamma-ray bursts (grbs), we used observations of on-axis short grbs (θobs=0) to predict the behavior of off- axis afterglows (θobs>0) with boxfit. we sampled from the distributions of inferred kinetic energies and densities of on-axis short grb afterglows for our simulation parameters. overall, the light curves demonstrate that when we incorporate the distributions of energies and densities from short grbs, there is a large diversity in expected light curve behavior. we find that for θobs=10°, the light curves peak at or above 10-2 mjy that can be detected by our most sensitive facilities; while for θobs=60°, the light curves peak at or above 10-4 mjy, which is beyond the reach of current facilities. ultimately, our results show the critical role timing plays in our observations, as well as the limited return of deeper observations past a certain depth. this is a proof-of-concept study, and we have developed a multi-use tool that allows for adaptation to other electromagnetic counterpart models. our results can be reproduced and also tested at other angles through user desired input. | on to off: predictions for the radio afterglows of neutron star mergers |
while much has been learned about the particle acceleration and emission processes at work during both the prompt and afterglow phases of gamma-ray bursts (grbs), important questions remain, some of which can be addressed by searches for the highest-energy photons from grbs using telescopes operating in the very high energy (vhe; e > 100 gev) range. veritas, an imaging atmospheric cherenkov telescope (iact) array located at the whipple observatory in southern arizona, has been performing follow-up observations of grbs since mid-2006 and continues to maintain an active grb observing program. in the context of the detection of grb 190114c by magic at energies above 300 gev, demonstrating that an important contribution to the physics of grbs that can be made by iacts, we review the veritas grb follow-up program. we discuss the development of analysis methods tailored to transient signals, and upper limits on the vhe emission from prominent bursts. these bursts include grb 130427a, for which the veritas limits constrain radiation mechanisms in the afterglow, and grb 150323a, for which the limits constrain properties of the environment in which the burst took place. | the veritas gamma ray burst follow-up program |
"we observed grb 191221b (laha et al., gcn 26534) with the australia telescope compact array (atca) at multiple frequencies and multiple epochs beginning on 2019 december 22 14:17 ut (0.73 days after the burst). we detect a varying radio counterpart at 5.5, 9.0, 16.7, and 21.2 ghz at a position consistent with the x-ray position (beardmore et al., gcn 26540) and optical position (lipunov et al., gcn 26537). we identify this source as the radio afterglow of grb 191221b. further analysis and observations are on-going. we thank the csiro staff for approving these observations." | grb 191221b: atca detection of the radio afterglow |
gamma ray bursts (grbs) can be used to address high priority scientific questions on the formation of the universe including: when did the star formation begin and how did it evolve? when and how did the intergalactic medium become re-ionized and what processes governed its early chemical enrichment? long grbs signal when a massive star collapses and provide an independent tracer of massive star formation. the grb afterglow is a bright beacon lasting a few days that can be used out to the highest redshifts to probe the intervening material from the host galaxy and intergalactic medium. the gamow explorer will detect and locate grbs from the z > 6 high redshift universe. a wide field x-ray telescope detects grbs and triggers a rapidly slewing spacecraft to point an infra-red telescope to obtain an arc second location and autonomously determine the redshift by searching for the lyman alpha dropout. for z >6 grbs a redshift alert will enable follow up by large telescopes. the gamow explorer will be proposed to the 2021 nasa midex opportunity, for launch in 2028. it will be a key component in the multi-messenger era of jwst, 30-m class telescopes and gravitational wave detectors. | the gamow explorer: a gamma-ray burst mission to investigate the high redshift universe |
long gamma-ray bursts (grbs) with a plateau phase in their x-ray afterglows obey a 3d relation, between the rest-frame time at the end of the plateau, t a , its corresponding x-ray luminosity, l a , and the peak luminosity in the prompt emission, l peak. this 3d relation identifies a grb fundamental plane whose existence we here confirm. here we include the most recent grbs observed by swift to define a “gold sample” (45 grbs) and obtain an intrinsic scatter about the plane compatible within 1σ with the previous result. we compare grb categories, such as short grbs with extended emission (see), x-ray flashes, grbs associated with supernovae, a sample of only long-duration grbs (132), selected from the total sample by excluding grbs of the previous categories, and the gold sample, composed by grbs with light curves with good data coverage and relatively flat plateaus. we find that the relation planes for each of these categories are not statistically different from the gold fundamental plane, with the exception of the sse, which are hence identified as a physically distinct class. the gold fundamental plane has an intrinsic scatter smaller than any plane derived from the other sample categories. thus, the distance of any particular grb category from this plane becomes a key parameter. we computed the several category planes with t a as a dependent parameter obtaining for each category smaller intrinsic scatters (reaching a reduction of 24% for the long grbs). the fundamental plane is independent from several prompt and afterglow parameters. | the fundamental plane for grb x-ray afterglows |
the transiting exoplanet survey satellite (tess) has proven to be an invaluable tool to detect extrasolar planets. however, the full-sky survey conducted by tess also lends itself to a different type of analysis - the detection of astrophysical periodic and transient events, such as variable stars, supernovae, and gamma-ray burst (grb) afterglows. using full-frame images (64 megapixels, exposure time: 30 minutes) from each 2300 square degree sector of tess's observations, we are developing an algorithm designed to search for transient sources at the pixel level. our method separates the time-series images into smaller groups over time and then calculates the per-pixel variance over the duration of each such group. by subtracting these variance maps across adjacent groups, we can mitigate systematic variability, such as that caused by scattered light and motion of the images due to differential velocity aberration. the remaining point sources in the differential variance maps correspond to variable stars and other transient sources. furthermore, we can sort these variables by timescale by changing the length of time (i.e. the number of images in each group) over which we calculate the variance. our algorithm represents a key first step in identifying transient sources directly from tess data. applications include identifying rare and short time-scale transients that might be missed by ground-based surveys, discovering new asteroids (which appear as streaks, rather than point sources, on the variance maps), and efficiently searching for optical counterparts of transients with poorly determined coordinates, like fast radio bursts and gravitational-wave events. future work will use machine learning to classify prospective transient events and prioritize them for follow-up observations. | using tess data to detect astrophysical transients |
at 09:07:37 ut on 14 may 2020, the fermi gamma-ray burst monitor (gbm) triggered and located grb 200514b (gcn 27736, fermi-gbm team). follow-up observations by the zwicky transient facility identified ztf20aazpphd as a potential optical counterpart to grb 200514b (ahumada et al., gcn 27737). ztf20aazpphd was subsequently observed by atlas, who found no evidence for rapid decline (smartt et al., gcn 27738), contrary to what expected for a short grb afterglow. we also verified that, when gbm triggered on grb 200514b, the source position for ztf20aazpphd as observed by gbm was occulted by earth and therefore unobservable. we therefore conclude that the optical transient ztf20aazpphd is unrelated to grb 200514b. | optical transient ztf20aazpphd is unrelated to grb 200514b |
the uvot is a modified richey-chretien 30 cm telescope that has a wide (17'x17') field of view and a microchannel plate intensified ccd operating in photon-counting mode (see details in roming et al. 2000spie.4140...76r, 2004spie.5165..262r, 2005ssrv..120...95r) on board the neil gehrels swift gamma ray burst mission (gehrels et al. 2004apj...611.1005g). the instrument is equipped with a filter wheel that includes a clear white filter; u, b, and v optical filters; uvw1, uvm2, and uvw2 uv filters; a magnifier; two grisms; and a blocked filter. although its primary mission is to measure the optical/uv afterglows of gamma-ray bursts, the wide field, 2.3" resolution, broad wavelength range (1700-8000 å), and ability to observe simultaneously with swift's x-ray telescope (burrows et al. 2005ssrv..120..165b) allow a broad range of science, including the study of hot or highly energetic stars. we have included clusters in the sample if they were observed for at least 0.8 ks in two of uvot's three nuv filters and where the field center was within 5' of the nominal cluster center, although some exceptions have been made to expand the sample. (2 data files). | vizier online data catalog: swift uvot stars survey. iii. galactic open clusters (siegel+, 2019) |
burst observed from grb 190114c on 14 january 2019. report of a paper in apj by nuria jordan et al. | news note: master observes gamma-ray burst afterglow |
i will present a summary of the extensive multi wavelength observations of the counterpart of gw170817 and its host galaxy. i will highlight how these observations unveiled the associated kilonova, and what the properties of the kilonova tell us about the geometry of the explosion and the synthesis of heavy elements. i will outline how long-term observations across the electromagnetic spectrum allowed the identification of an off-axis grb afterglow, and how in turn this provides central insight into the nature of short duration gamma-ray bursts and their jets. finally, i will demonstrate how observations of the environment of the burst and its host galaxy offer significant additional astrophysical utility by providing vital constraints on the binary evolution pathways leading to the formation of binary and on the distance to the host galaxy. | optical/x-ray observations of gw170817 and its environment |
at 23:04:55.34 ut on 20 january 2020, the fermi gamma-ray burst monitor (gbm) triggered and located grb 200120a (trigger 601254300 / 200120962). grb 200120a was also detected by insight/hmxt (gcn 26840) and astrosat/czti (gcn 26851), and localized by the ipn (gcn 26856). approximately 820 s after the gbm trigger, srg/erosita detected and localized an x-ray transient consistent with being the afterglow of grb 200120a (weber et al. 2019, gcn 26988). the fermi gbm final real-time localization (gcn 26831) is consistent with the srg/erosita position. the angle from the fermi lat boresight at the gbm trigger time is 148 degrees. the gbm light curve shows a broad, single-peaked structure with a duration (t90) of about 13 s (50-300 kev). the time-averaged spectrum from t0-6. to t0+10. s is best fit by a power law function with an exponential high-energy cutoff. the power law index is -0.92 +/- 0.10 and the cutoff energy, parameterized as epeak, is 239 +/- 22 kev. the event fluence (10-1000 kev) in this time interval is (9.4 +/- 0.4)e-06 erg/cm^2. the 1-sec peak photon flux measured starting from t0+3.0 s in the 10-1000 kev band is 13 +/- 1 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 200120a: fermi gbm observation |
despite a general framework for describing gamma-ray burst (grb) afterglows, the nature of the compact object and the mechanism behind the grb prompt emission remain a mystery. the striped jet model is a promising venue to investigate many of these pressing questions since it gives a robust prediction of the relation of jet acceleration, magnetization and dissipation profile as a function of distance. here, we propose to use the afterglow observations constraining the jet properties at the large scales where the jet starts interacting with the ambient gas to (i) test the striped jet model for the grb flow and (ii) study its predictions for the prompt emission and the central engine. | connecting the early afterglow to the prompt grb and the central engine |
grb 220412b is an extremely short duration gamma-ray burst lasting just 140ms. prompt x-ray and optical follow-up revealed no corresponding afteglow to deep limits at early times. however, our vla observations at 10 days after trigger reveal a bright (~380 ujy) uncataloged radio source offset just a few arcseconds from the center of the bat localisation. these observations are consistent with an `off-axis' grb wherein the jet is not directly pointed towards earth. the afterglow is initially beamed away from the observer and is later seen to rise as the relativistic doppler beaming lessens. the radio source is not coincident with any known galaxy nor optical emission in archival images. we therefore request observations with chandra to explore its multi-wavelength properties and potentially confirm it as the grb afterglow in the local universe. | confirmation of a candidate nearby off-axis short grb |
when two compact objects neutron stars or black holes merge, will they emit light? a recent study looks at a neglected factor that could affect the answer: electric charge.dark or light?artists impression of two merging neutron stars producing a gamma-ray burst. [national science foundation/ligo/sonoma state university/a. simonnet]most theories agree that a compact binary containing a neutron star can emit light when it merges. this is because these systems contain lots of neutron-rich matter that can then radiate in the final stages of merger, in the form of gamma-ray bursts, kilonovae, and afterglows.but what about compact binaries containing two black holes? or so-called plunging black-holeneutron-star mergers in which the neutron star plunges directly into the black hole before it can be disrupted? are these mergers all doomed to darkness?possible chargenot according to bing zhang, a scientist at university of nevada las vegas. recently, zhang proposed that black holes might carry electric charge in a surrounding magnetosphere. as charged black holes spiral around and around each other during a merger, they could generate electromagnetic radiation: a characteristic signal that rises sharply just before merger.now zhang is back with a generalized model for the merger of charged compact objects, which also explores possible signatures from electrically charged neutron stars. in a new study, he works out the details and reports on where we might be able to detect these signals.searching for a signalall compact binaries containing a neutron star should emit radiation from electric charge, since neutron stars are definitely charged theyre essentially spinning magnets. but for most systems containing a neutron star, zhang demonstrates, the radiation associated with the objects charge will be non-detectable, since its so much dimmer than other electromagnetic signatures from merger (like a gamma-ray burst).the crab pulsar is a highly magnetized, spinning neutron star that powers the crab nebula seen in this composite image. [x-ray: nasa/cxc/sao/f.seward; optical: nasa/esa/asu/j.hester a.loll; infrared: nasa/jpl-caltech/univ. minn./r.gehrz]theres hope, though, in the scenario of a plunging neutron-starblack-hole merger. if the neutron star is less than 20% the size of the black hole, it can be consumed whole, preventing any of the typical electromagnetic signatures from occurring. in this case, the radiation from the charged, inspiralling neutron star is the only electromagnetic signal present.if the neutron star in such a system has a magnetic field similar to that of the crab pulsar possible in young star clusters the charge signal can reach detectable levels, according to zhangs calculations. in fact, its possible that we could observe such a signal as a fast radio burst, the mysterious millisecond radio bursts that weve seen originating from beyond our galaxy.looking aheadmany unknowns are still present in this picture. how is the electric radiation converted into observable emission? how commonly do we expect plunging neutron-starblack-hole mergers to occur as described? will we be able to link radiation from charged mergers to a gravitational-wave chirp?one thing is for certain: if we can, indeed, observe the light from charge in a compact-binary merger, this would provide an exciting new opportunity to further probe these distant, exotic systems.citationcharged compact binary coalescence signal and electromagnetic counterpart of plunging black holeneutron star mergers, bing zhang 2019 apjl 873 l9. doi:10.3847/2041-8213/ab0ae8 | compact objects charging toward merger |
we propose a chandra too program to observe short grbs detected by swift in order to localize their x-ray afterglow with sub-arcsecond accuracy. our too program will increase the number of short grbs having an unambiguous host galaxy identification, and provide a less biased sample of grb host galaxies. we request a maximum of 2 toos for 20 ksec each. our trigger criteria are 1) swift short grbs localized by swift/xrt and 2) no afterglow confirmation in optical within 24 hours after the burst. we request <2 days response to our too, so that the afterglow can be observed while still bright. | chandra sub-arcsecond localization of swift short grbs |
at 15:03:28 ut, the swift burst alert telescope (bat) triggered and located a burst from soft gamma repeater sgr swift j1818.0-1607 (trigger=972614). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 274.550, -16.193 which is ra(j2000) = 18h 18m 12s dec(j2000) = -16d 11' 32" 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 100 ms. the peak count rate was ~1000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 15:04:27.5 ut, 59.0 seconds after the bat trigger. using promptly downlinked data we find an x-ray source with an enhanced position: ra, dec 274.5010, -16.1314 which is equivalent to: ra(j2000) = 18h 18m 00.23s dec(j2000) = -16d 07' 53.0" with an uncertainty of 3.0 arcseconds (radius, 90% containment). this location is 279 arcseconds from the bat onboard position, consistent with the known position of swift j1818.0-1607. 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 1.35 x 10^22 cm^-2 (willingale et al. 2013). uvot took a finding chart exposure of 150 seconds with the white filter starting 62 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 none of the xrt error circle. no correction has been made for the large, but uncertain, extinction expected. swift is currently monitoring this source every 3 days under a too program. | swift detection of a burst from sgr swift j1818.0-1607 |
spectroscopic study of prompt gamma ray emission of grbs, while providing valuable information, has not proven adequate to fully discriminate between various emission models. measurement of polarisation simultaneously with spectroscopy, however, adds a very important dimension that allows one to put strong constraints on the emission mechanism, composition and geometry of the grb outflow. astrosat cadmium zinc telluride imager (czti) is actively measuring linear polarisation of grbs in 100-400 kev range. this paper presents the results of spectro-polarimetric analysis of grb 160325a and grb 160821a. (a) in grb 160325a, a transition is seen in the spectrum from thermal+non-thermal to pure non-thermal emission, with an accompanying change in polarisation. a composite modelling of polarisation, spectrum and the afterglow light curve allows us to infer that the outflow is baryon dominated with mild magnetisation. (b) grb 160821a, the third most energetic burst detected by the fermi, exhibited (i) high linear polarisation, and (ii) near-orthogonal transition of polarisation angle twice during a single emission episode. the emission mechanism that best explains these observations is synchrotron radiation produced in a magnetic field which is highly ordered on angular scales of 1/$\gamma$. | time resolved spectro-polarimetry of grb prompt emission |
at 09:51:06 ut, the swift burst alert telescope (bat) triggered and located grb 211129a (trigger=1085430). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 274.557, +31.776 which is ra(j2000) = 18h 18m 14s dec(j2000) = +31d 46' 33" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve shows 3 major peaks with a duration of about 200 sec. the peak count rate was ~1400 counts/sec (15-350 kev), at ~3 sec after the trigger. the xrt began observing the field at 09:52:19.7 ut, 73.5 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 274.58129, 31.78820 which is equivalent to: ra(j2000) = 18h 18m 19.51s dec(j2000) = +31d 47' 17.5" with an uncertainty of 4.0 arcseconds (radius, 90% containment). this location is 86 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/1085430. 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 1.41e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 83 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 0.082. 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 211129a: swift detection of a burst |
at 20:05:28 ut, the swift burst alert telescope (bat) triggered and located grb 220117b (trigger=1093611). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 191.947, -28.744 which is ra(j2000) = 12h 47m 47s dec(j2000) = -28d 44' 38" 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 ~1000 counts/sec (15-350 kev), at ~1 sec after the trigger. the xrt began observing the field at 20:07:04.0 ut, 95.9 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 191.9514, -28.7446 which is equivalent to: ra(j2000) = 12h 47m 48.34s dec(j2000) = -28d 44' 40.6" with an uncertainty of 6.5 arcseconds (radius, 90% containment). this location is 14 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 4.69e-10 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 104 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. data from the 2.7'x2.7' sub-image are not available at this time. 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 0.075. 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 220117b: swift detection of a burst |
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