abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
since the lp-nova models were proposed, and the short gamma-ray burst (sgrb) afterglows were confirmed, people have actively made searches for the evidence of the existence of lp-novae among the optical (or near-infrared) counterparts of sgrbs. in this paper, we first summarize these observational progresses before 2012 in section 2. in section 3 and 4, we respectively introduce the basic properties of grbs 130603b and 060614, as well as the theoretical interpretation for their near-infrared (nir) counterparts, and their nir excess may be the signature of the existence of lp-novae. in section 5, we describe the basic properties of grb 080503, and the theoretical interpretation for its optical and x-ray counterparts, and the later re-brightening of its optical and x-ray light curves is explained as the ejecta radiation (merger-nova radiation) of magnetar heating after the neutron star merging. if the interpretations for the sgrb-associated optical and infrared counterparts are correct, they may provide the first series of direct evidence to show that sgrbs and some special lgrbs are originated from the compact star mergers. besides lp-novae (and merger-novae), the high-speed orbital motion before the compact star merging and the merger itself will produce strong gravitational-wave bursts (gwbs). in the coming era of gravitational wave detection, the theoretical and observational studies on the electromagnetic counterparts of compact star mergers will receive more and more attentions. due to the larger uncertainty of gwb's location, the lp-novae associated with gwbs can serve as the best candidates for the precise location of gwbs. the fast developing high-cadence and wide-field optical-nir surveys will make effective explorations on the lp-novae and similar phenomena, and interact the detection and research of gravitational waves. therefore, in the last section we present the methods for the future detections of lp-novae, and the prospect of their multi-messenger detections. | research developments in li-paczyński novae (ii): observational aspect |
at 19:07:13 ut, the swift burst alert telescope (bat) triggered and located grb 210702a (trigger=1058804). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 168.570, -36.741 which is ra(j2000) = 11h 14m 17s dec(j2000) = -36d 44' 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 100 sec. the peak count rate was ~10,000 counts/sec (15-350 kev), at ~2 sec after the trigger. the xrt began observing the field at 19:08:49.2 ut, 95.5 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 168.5813, -36.7474 which is equivalent to: ra(j2000) = 11h 14m 19.51s dec(j2000) = -36d 44' 50.6" with an uncertainty of 11.0 arcseconds (radius, 90% containment). 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 1.00e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 45 seconds with the u filter starting 315 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 11:14:18.83 = 168.57846 dec(j2000) = -36:44:48.8 = -36.74690 with a 90%-confidence error radius of about 0.61 arc sec. this position is 8.4 arc sec. from the center of the xrt error circle. the estimated magnitude is 11.72 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.121. burst advocate for this burst is a. y. lien (amy.y.lien at nasa.gov). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210702a: swift detection of a burst with a bright optical counterpart |
the work describes an investigation of afterglow of various luminophores under influence of pulsed x-ray radiation of nanosecond duration. as a source of radiation a pulsed x-ray “yasen 01” apparatus is applied. maximum impulse current of an x-ray tube is 300 a. maximum electron energy is 120 kev. half-height pulse duration of an x-ray burst is about 30 ns. a pulse repetition rate is up to 4 khz. two types of x-ray luminophores based on gadolinium oxysulfide gd2o2s:tb and cesium iodide csi:tl have been investigated. the novelty of the work is use of a fast-acting solid-state semiconductor photomultiplier. it allows recording changes of luminophores luminosity in the nanosecond time range. the photomultiplier is characterized by having two discreet outputs for measuring quickly and slowly time-changing light flows. presence of two signal outputs allows recording changes of luminophores luminosity both during fast nanosecond excitation and during long-time afterglow. obtained data about the nature of afterglow of investigated luminophores makes it possible to select the best one for use in conjunction with a pulsed x-ray apparatus with a high pulse repetition rate. | research of luminophores afterglow under influence of pulsed x-ray radiation of nanosecond duration |
two neutron stars merge somewhere in the universe approximately every 10 to 100 seconds, creating explosions potentially observable in gravitational waves and across the electromagnetic spectrum. these observations are in- trinsically connected to the fate of the merger. this thesis focuses on using these different signatures to shed light on the aftermath of these explosions and several fundamental questions in astrophysics. i begin by reviewing the different signatures expected from a binary neutron star merger, describing the impact of different merger outcomes in detail. in particular, i examine the x-ray afterglows of gamma-ray bursts and their connection to nascent neu- tron stars. i describe work introducing a new method to study the behaviour of nuclear matter in a previously unexplored regime. this work has led to tentative evidence for the presence of temperature-dependent phase transi- tions. i introduce a new model incorporating radiative losses with energy injection from a nascent neutron star that self-consistently explains x-ray flares seen in gamma-ray bursts, plateau diversity, and x-ray afterglow data. i describe a bayesian framework for identifying the mechanism responsible for powering the x-ray afterglow of gamma-ray bursts. i apply this method to grb140903a, demonstrating that grb140903a definitively produced an infinitely stable neutron star. i also describe work introducing a new waveform model for the gravitational-wave signature of such a neutron star and how we can use x-ray observations to guide our searches for gravitational waves. i also include work on interpreting the nature of two transients, cdf-s xt1 and at2020blt. the latter likely being the afterglow of a low-efficiency long gamma-ray burst, with prompt emission potentially weaker than 98.4% of the gamma-ray burst population hinting at a sub-population of very-low effi- ciency gamma-ray bursts. on the other hand, i show that cdf-s xt1 is likely the x-ray afterglow of an off-axis short gamma-ray burst. as potentially the first orphan afterglow observed in x-rays, and at z = 2.23, one of the most distant binary neutron star merger ever observed this event has several im- plications. i discuss these implications alongside the prospect of identifying other off-axis afterglows. the works presented in this thesis are shedding significant insight into the presence and dynamics of nascent neutron stars and improving our understanding of the biggest explosions in the universe. i conclude by discussing these insights, some closing thoughts and the next big questions in this field. | the observational signatures of nascent neutron stars |
strong spectral softening has been revealed in the late x-ray afterglows of some gamma-ray bursts (grbs). the scenario of x-ray scattering around the circumburst dusty medium has been supported by previous works due to its overall successful prediction of both the temporal and spectral evolution of some x-ray afterglows. to further investigate the observed feature of spectral softening we now systematically search the x-ray afterglows detected by the x-ray telescope aboard swift and collect 12 grbs with significant late-time spectral softening. we find that dust scattering could be the dominant radiative mechanism for these x-ray afterglows regarding their temporal and spectral features. for some well-observed bursts with high-quality data, the time-resolved spectra could be well-produced within the scattering scenario by taking into account the x-ray absorption from the circumburst medium. we also find that during spectral softening the power-law index in the high-energy end of the spectra does not vary much. the spectral softening is mainly manifested by the spectral peak energy continually moving to the soft end. | on the late-time spectral softening found in x-ray afterglows of gamma-ray bursts |
at 09:18:18 ut, the swift burst alert telescope (bat) triggered and located grb 210822a (trigger=1069788). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 304.476, +5.265 which is ra(j2000) = 20h 17m 54s dec(j2000) = +05d 15' 54" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 30 sec. the peak count rate was ~38000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 09:19:32.7 ut, 74.6 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 304.4377, 5.2786 which is equivalent to: ra(j2000) = 20h 17m 45.05s dec(j2000) = +05d 16' 43.0" with an uncertainty of 11.9 arcseconds (radius, 90% containment). this location is 145 arcseconds from the bat onboard position, within the bat error circle. no event data are yet available to determine the column density using x-ray spectroscopy. the initial flux in the 0.1 s image was 1.25e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 250 seconds with the u filter starting 297 seconds after the bat trigger. an afterglow candidate has been found in the initial data products with a magnitude of u = 13.81 +/- 0.03. no correction has been made for the expected extinction corresponding to e(b-v) of 0.162. the preliminary uvot position is ra=304.43748, dec = 5.28337 (j2000), which is equivalent to: ra = 20h 17m 45.0s, dec = +05d 17m 00.1s (j2000) with an uncertainty of about an arcsecond. burst advocate for this burst is k. l. page (klp5 at leicester.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 210822a: swift detection of a burst with an optical afterglow |
context. the short burst grb 130912a was detected by swift, fermi satellites, and several ground-based optical telescopes. its x-ray light curve decayed with time normally. the optical emission, however, displayed a long-term plateau.aims: we examine the physical origin of the x-ray and optical emission of short grb 130912a.methods: the afterglow emission was analysed and the light curve fitted numerically.results: the canonical forward-shock model of the afterglow emission accounts for the x-ray and optical data self-consistently, so the energy injection model that has been widely adopted to interpret the shallowly decaying afterglow emission is not needed.conclusions: the burst was born in a very-low density interstellar medium, which is consistent with the compact-object merger model. significant amounts of the energy of the forward shock were given to accelerate the non-thermal electrons and amplify the magnetic fields (i.e., ɛe ~ 0.37 and ɛb ~ 0.16, respectively), which are much more than those inferred in most short-burst afterglow modelling and can explain why the long-lasting optical afterglow plateau is rare in short grbs. | the long-lasting optical afterglow plateau of short burst grb 130912a |
this paper presents a catalogue of gamma-ray bursts (grbs) that were detected by the instruments onboard the lomonosov space observatory. the lomonosov mission gave the first experience of not only multi-wavelength (from optical to gamma) observations of grbs but also multi-messenger observations of extreme phenomena and grbs. the detailed light curves and energy spectra of the detected grbs are presented. the results of the prompt, early an afterglow optical observations of several grbs are discussed. | lomonosov grb catalogue: the first experience of prompt emission multi-wavelength observations |
grb 130427a was the most luminous gamma-ray burst detected in the last 30 years. with an isotropic energy output of 8.5 × 10 53 erg and redshift of 0.34, it combined very high energetics with a relative proximity to earth in an unprecedented way. sensitive x-ray observatories such as xmm-newton and chandra have detected the afterglow of this event for a record-breaking baseline longer than 80 million seconds. the light curve displays a simple power-law over more than three decades in time. in this presentation, we explore the consequences of this result for a few models put forward so far to interpret grb 130427a, and more in general the implication of this outcome in the context of the standard forward shock model. | challenging the forward shock model with the 80 ms follow up of the x-ray afterglow of gamma-ray burst 130427a |
a widely accepted model for producing gamma-ray bursts (grbs) is based on the dissipation of an ultra-relativistic jet. synchrotron emission is believed to be the dominant radiation process for the main emission components of grbs, i.e. prompt gamma-rays, reverse shock emission and afterglow. although the presence of strong magnetic fields in the emission regions is crucial to produce the bright emission, the origin and its role in the dynamics are still unknown. understanding the nature of the relativistic jet, especially the energy content, acceleration and collimation, is a major focus of international theoretical and observational effort. polarisation is one of characteristics of synchrotron emission, and polarimetric observations would allow us to study the magnetic field structure and energy distribution in grb jets. | magnetic fields in gamma-ray bursts and their polarised emission |
for four types of grbs, namely high-luminosity, low-luminosity, standard and failed grbs, we calculated their radio afterglow light curves. meanwhile, considering contributions from host galaxies in radio bands, we statistically investigated the effect of hosts on radio afterglows. it is found that a tight anti-correlation exists between the ratio of radio flux (rrf) of host galaxy to the total radio afterglow peak flux and the observed frequency. using this method, the host flux densities of those bursts without host measurements can be estimated at low or medium frequencies. we predicted that almost all types of radio afterglows, except that of low-luminosity grbs, can be observed by fast up to z = 15 or even more. fast is expected to significantly expand the samples of grb radio afterglows and host galaxies. | gamma-ray bursts: radio afterglow and host galaxy study with the fast telescope |
being the most extreme explosions in the universe, gamma-ray bursts (grbs) provide a unique laboratory to study various plasma physics phenomena. the complex light curve and broad-band, non-thermal spectra indicate a very complicated system on the one hand, but, on the other hand, provide a wealth of information to study it. in this chapter, i focus on recent progress in some of the key unsolved physical problems. these include: (1) particle acceleration and magnetic field generation in shock waves; (2) possible role of strong magnetic fields in accelerating the plasmas, and accelerating particles via the magnetic reconnection process; (3) various radiative processes that shape the observed light curve and spectra, both during the prompt and the afterglow phases, and finally (4) grb environments and their possible observational signature. | plasmas in gamma-ray bursts: particle acceleration, magnetic fields, radiative processes and environments |
we try to identify the nature of high redshift long gamma-ray bursts (lgrbs) host galaxies by comparing the observed abundance ratios in the interstellar medium with detailed chemical evolution models accounting for the presence of dust. we compared measured abundance data from lgrb afterglow spectra to abundance patterns as predicted by our models for different galaxy types. we analysed in particular [x/fe] abundance ratios (where x is c, n, o, mg, si, s, ni, zn) as functions of [fe/h]. different galaxies (irregulars, spirals, ellipticals) are, in fact, characterised by different star formation histories, which produce different [x/fe] ratios ("time-delay model"). this allows us to identify the morphology of the hosts and to infer their age (i.e. the time elapsed from the beginning of star formation) at the time of the grb events, as well as other important parameters. relative to previous works, we use newer models in which we adopt updated stellar yields and prescriptions for dust production, accretion and destruction. we have considered a sample of seven lgrb host galaxies. our results have suggested that two of them (grb 050820, grb 120815a) are ellipticals, two (grb 081008, grb 161023a) are spirals and three (grb 050730, grb 090926a, grb 120327a) are irregulars. we also found that in some cases changing the initial mass function can give better agreement with the observed data. the calculated ages of the host galaxies span from the order of 10 myr to little more than 1 gyr. | the nature of grb host galaxies from chemical abundances |
we present x-ray and optical observations of the short duration gamma-ray burst grb 071227 and its host at z = 0.381, obtained using swift, gemini south, and the very large telescope. we identify a short-lived and moderately bright optical transient, with flux significantly in excess of that expected from a simple extrapolation of the x-ray spectrum at 0.2-0.3 d after burst. we fit the sed with afterglow models allowing for high extinction and thermal emission models that approximate a kilonova to assess the excess' origins. while some kilonova contribution is plausible, it is not favoured due to the low temperature and high luminosity required, implying superluminal expansion and a large ejecta mass of ∼0.1 m⊙. we find, instead, that the transient is broadly consistent with power-law spectra with additional dust extinction of e(b - v) ∼ 0.4 mag, although a possibly thermal excess remains in the z band. we investigate the host, a spiral galaxy with an edge-on orientation, resolving its spectrum along its major axis to construct the galaxy rotation curve and analyse the star formation and chemical properties. the integrated host emission shows evidence for high extinction, consistent with the afterglow findings. the metallicity and extinction are consistent with previous studies of this host and indicate the galaxy is a typical, but dusty, late-type sgrb host. | an unusual transient following the short grb 071227 |
we consider a sample of 107 gamma-ray bursts (grbs) for which early ultra-violet emission was measured by swift and extrapolate the photon intensity to lower energies. protons accelerated in the grb jet may interact with such photons to produce charged pions and subsequently ultra high energy neutrinos {\varepsilon }ν ≥slant {10}16 ev. we use simple energy conversion efficiency arguments to predict the maximal neutrino flux expected from each grb. we estimate the neutrino detection rate at large area radio based neutrino detectors and conclude that the early afterglow neutrino emission is too weak to be detected even by next generation neutrino observatories. | ultra-high energy neutrinos from gamma-ray burst afterglows using the swift-uvot data |
compact binary mergers, with neutron stars or neutron star and black-hole components, are thought to produce various electromagnetic counterparts: short gamma-ray bursts (grbs) from ultra-relativistic jets followed by broadband afterglow; semi-isotropic kilonova from radioactive decay of r-process elements; and late time radio flares; etc. if the jets from such mergers follow a similar power-law distribution of lorentz factors as other astrophysical jets then the population of merger jets will be dominated by low-γ values. the prompt gamma-rays associated with short grbs would be suppressed for a low-γ jet and the jet energy will be released as x-ray/optical/radio transients when a shock forms in the ambient medium. using monte carlo simulations, we study the properties of such transients as candidate electromagnetic counterparts to gravitational wave sources detectable by ligo/virgo. approximately 78% of merger-jets result in failed grb with optical peaks 14-22 magnitude and an all-sky rate of 2-3 per year. | low-γ jets from compact binary mergers as candidate electromagnetic counterparts to gravitational wave sources |
one of the central scientific goals of the next-generation cherenkov telescope array (cta) is the detection and characterization of gamma-ray bursts (grbs). cta will be sensitive to gamma rays with energies from about 20 gev, up to a few hundred tev. the energy range below 1 tev is particularly important for grbs. cta will allow exploration of this regime with a ground-based gamma-ray facility with unprecedented sensitivity. as such, it will be able to probe radiation and particle acceleration mechanisms at work in grbs. in this contribution, we describe posytive, the population synthesis theory integrated project for very high-energy emission. the purpose of the project is to make realistic predictions for the detection rates of grbs with cta, to enable studies of individual simulated grbs, and to perform preparatory studies for time-resolved spectral analyses. the mock grb population used by posytive is calibrated using the entire 40-year dataset of multi-wavelength grb observations. as part of this project we explore theoretical models for prompt and afterglow emission of long and short grbs, and predict the expected radiative output. subsequent analyses are performed in order to simulate the observations with cta, using the publicly available ctools and gammapy frameworks. we present preliminary results of the design and implementation of this project. | posytive -- a grb population study for the cherenkov telescope array (icrc-2019) |
accretion on to black holes powers some of the most luminous objects in the universe. in this thesis i present a series of works aimed at constraining the properties of black hole accretion in a variety of astrophysical systems. numerical methods are vital for studying the multi-scale and non-linear physics of these systems. first i introduce discogr, the first implementation of numerical general relativistic magnetohydrodynamics on a moving mesh. discogr is capable of efficiently and accurately simulating highly supersonic thin accretion disks, the objects responsible for many luminous accretion events. i apply discogr to study minidisks: accretion disks around a single member of a binary black hole system. spiral shock waves, excited by tidal forces from the binary companion, propagate throughout the disk, causing efficient accretion by purely hydrodynamical means. the shock-driven accretion has an effective alpha parameter of the order 0.01, comparable with accretion driven by the magnetorotational instability. furthermore, shocks near the black hole contribute to a radiative signature brighter in the hard x-rays than the standard novikov-thorne model. finally i present an analysis of gamma-ray burst (grb) x-ray afterglow light curves. the analysis fits the data from the swift-xrt directly to a suite of hydrodynamical simulations, constraining the jet opening angle and, for the first time, the viewing angle of these events. i find typically the viewing angle to be 0.57 of the jet opening angle. observing a grb off-axis can reduce the inferred energy of the central engine, thought to be a neutron star or accreting black hole, by up to a factor of four. | numerical simulations of black hole accretion |
i review how polarization signals have been discussed in the research field of gamma-ray bursts (grbs). i mainly discuss two subjects in which polarimetry enables us to study the nature of relativistic jets. (1) jet breaks: gamma-ray bursts are produced in ultra-relativistic jets. due to the relativistic beaming effect, the emission can be modeled in a spherical model at early times. however, as the jet gradually slows down, we begin to see the edge of the jet together with polarized signals at some point. (2) optical flash: later time afterglow is known to be insensitive to the properties of the original ejecta from the grb central engine. however, a short-lived, reverse shock emission would enable us to study the nature of of grb jets. i also briefly discuss the recent detection of optical circular polarization in grb afterglow. | polarized emission from gamma-ray burst jets |
the combo-relation is a tight relation involving the prompt emission spectral peak energy ep,i and the x-ray afterglow plateau luminosity l0 and its rest-frame duration τ, and the late power-law decay index α. to explain its features, in this work we investigate the external shock scenario, i.e. the synchrotron emission from the electrons accelerated in a relativistic shock propagating through a cold external medium with density n and interacting with the magnetic field b associated with the turbulent plasma. three assumptions were introduced: (1) the homologous shock expansion; (2) an electron power-law distribution over a large range of frequencies; and (3) a power-law dependence on the shock radius of b and n. first, we show how the values of ep,i, l0 and τ depend on combinations of the initial values of the magnetic field b0, shock radius r0 and medium density n0, as well as the shock lorentz factor γ0 and the electron distribution. then, we prove that the combo-relation results from the relationship between ep,i, l0 and τ and the corresponding comoving quantities that scale with γ0. finally, through monte carlo simulations, we deduce the typical model parameters, for example, b_0=4.6^{+253.9}_{-4.5} g, r_0=7.0^{+34.4}_{-5.8}× 10^{13} cm and n_0=10.00^{+7694.62}_{-9.99} cm-3, all in agreement with the results obtained in the literature. we conclude that, within the external shock scenario and its flaws, the combo-relation represents a new tool for investigating the physics of the prompt and afterglow emissions and for inferring the properties of the gamma-ray-burst external medium. | physical insight into the combo-relation |
long-duration gamma-ray bursts (grbs) are excellent probes to study dust extinction due to their occurrence in star-forming regions and having simple synchrotron emission spectra. inclusion of spectroscopic data to the grb x-ray to the infrared spectral energy distribution (sed) could better define the continuum and confirm extinction feature. a preliminary sed analysis of grb afterglows targeted with the vlt/x-shooter spectrograph finds that all the 60% of extinguished bursts fit-well with featureless extinction curves. the longer wavelength coverage from ultraviolet to the near-infrared of x-shooter helps to derive individual extinction curves and determine the total-to-selective extinction, rv precisely, suggesting extinction curves steeper (with a mean of rv = 2.66 ± 0.10) than the small magellanic cloud. moreover, addition of more data to the study of dust-to-metals ratios in grb afterglows, quasar absorbers, and multiply lensed galaxies still shows the dust-to-metals ratios close to the galactic value (with a mean value of log - 21.2cm-2mag-1), hinting short time delay between metals and dust formation. such studies demonstrate the strength of using grb afterglows to study dust origin and its properties the from low to high redshift universe. | grb afterglows: dust extinction properties from the low to high redshift universe |
at 04:43:57 ut, the swift burst alert telescope (bat) triggered and located grb 210226a (trigger=1034721). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 124.138, +57.577 which is ra(j2000) = 08h 16m 33s dec(j2000) = +57d 34' 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 30 sec. the peak count rate was ~3400 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 04:45:35.3 ut, 98.1 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 124.1144, 57.5839 which is equivalent to: ra(j2000) = 08h 16m 27.46s dec(j2000) = +57d 35' 02.2" with an uncertainty of 2.1 arcseconds (radius, 90% containment). this location is 51 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 (5.24 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 3.2 (+1.84/-1.67) x 10^21 cm^-2 (90% confidence). 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 0.048. 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 210226a: swift detection of a burst |
in 1977, blandford and znajek showed how the spin energy of a rotating black hole may be extracted electromagnetically through a magnetic field that threads the black hole horizon. a characteristic feature of this mechanism is that, under certain fairly general conditions, the energy loss rate decays exponentially. we looked precisely for such behavior in the x-ray light curves of long and ultra long duration gamma-ray bursts (grbs) observed with the xrt instrument on board the swift satellite, and found that almost 30% of xrt light curves show an exponential decay before they reach the afterglow plateau. a similar behavior (fast rise exponential decay-fred) was observed in γ -rays with the batse instrument aboard the cgro satellite. we consider both of these findings as the signature of the blandford-znajek mechanism in action in the central engine of grbs. | the signature of the blandford-znajek mechanism in grb light curves |
we present the statistics of the ratio, r, between the prompt and afterglow “plateau” fluxes of gamma-ray bursts (grbs). we define this as the ratio of the mean prompt energy flux in swift bat and the swift xrt one, immediately following the steep transition between these two states and the beginning of the afterglow stage referred to as the “plateau”. like the distribution of many other grb observables, the histogram of r is log-normal with maximum at a value {{r}m}≃ 2000, fwhm of about two decades, and with the entire distribution spanning about five decades in the value of r. we note that the peak of the distribution is close to the proton-to-electron mass ratio ({{r}m}≃ {{m}p}/{{m}e}=1836), as proposed to be the case in an earlier publication, on the basis of a specific model of the grb dissipation process. it therefore appears that, in addition to the values of the energy of peak luminosity {{e}pk}∼ {{m}e}{{c}2}, grbs present us with one more quantity with an apparent characteristic value. the fact that the values of both these quantities ({{e}pk} and r) are consistent with the same specific model invoked to account for the efficient conversion of their relativistic proton energies to electrons argues favorably for its underlying assumptions. | the statistics of bat-to-xrt flux ratio in grbs: evidence for a characteristic value and its implications |
the space-based multi-band astronomical variable objects monitor (svom) project is a dedicated satellite developed at the cooperation of china and france, aim to make prompt multi-band observations of gamma-ray bursts (grbs), the afterglows and other high-energy transient astronomical events. the visible telescope (vt) is one of the four payloads onboard the svom. vt is designed to observe the afterglows of grbs both in the visible and near infrared bands simultaneously. the telescope can reach a limiting magnitude of +22.5mv and provide the redshift indicators for high-z (z<4) grbs. vt is also designed to measure the relative performance errors (rpes) for the satellite attitude and orbit control system (aocs), aiming to improve the pointing stability of the platform during observation. vt adopts a ritchey-chrétien (rc) catadioptric optical configuration with a 440mm aperture and uses the dichroic prism before the focal plane to split the incident light into blue (visible) and red (near infrared) band. two fine guidance sensor (fgs) ccds are mounted beside the main ccd on the blue band focal plane of vt and provide sub-arcsecond pixel resolution. fiber reinforced plastic (cfrp) composites is selected as the material of vt's main structure to ensure enough stiffness and strength during launch. the electrical video processing circuit is carefully designed to make the readout noise below 6e-/pix (rms) in 100s exposure time. active and passive thermal control are used together to ensure the optical performance and thermoelectric cooler (tec) is adopted to control the main ccds working temperature below -65°c to reduce the noise. this paper provides a comprehensive overview of the scientific requirements and the key instrument design aspects of optics, main structure, electrics, thermal control, performance test and validation results of vt. | the visible telescope onboard the chinese-french svom satellite |
phenomenological properties of gamma-ray bursts (grb) are briefly reviewed and observations of grb optical afterglow and other transients in abastumani astrophysical observatory are discussed. in particular, the catalog of observations in 2012-2015, and some results including the final photometry of the optical afterglow of grb 140801a are presented. | observations of gamma-ray bursts in abastumani observatory |
afterglows of gamma-ray bursts (grbs) from population iii (pop iii) stars could reveal the formation history and properties of these first generation stars. through detailed simulation, we predict the prospects of detecting these afterglows with a range of established, existing and upcoming telescopes across the spectrum from radio waves to x-rays. the simulations show that the afterglow light curves of pop iii grbs at high redshift (≳8) are very similar to those of pop i/ii grbs at lower redshift (∼2), with the distinction that lyα absorption at pop iii redshifts removes any optical [and some near-infrared (nir)] component. we calculate that within a single field of view (fov) of the australian square kilometre array pathfinder (askap) telescope there will be on average four detectable pop iii grb afterglows. this is the product of askap's large fov and excellent sensitivity at wavelengths where the afterglows are very long-lasting. we show that the exceptional sensitivity of the james webb space telescope (jwst) near-infrared camera will make this the optimal instrument for afterglow follow-up and redshift measurement, while jwst near-infrared spectrograph will be able to detect the absorption features of pop iii-enriched environments in 70 per cent of directed pop iii grb afterglows. we also find that the atacama large millimetre array is very poorly suited to observe these afterglows, and that the spectrum-roentgen-gamma 4 yr all-sky x-ray survey has a 12 per cent chance of detecting an orphan pop iii grb afterglow. the optimal strategy for detecting, identifying and studying pop iii grb afterglows is to have jwst attempt nir photometry of afterglows with a detected radio component but no detected optical component. | multiwavelength detectability of pop iii grbs from afterglow simulations |
at 11:26:59 ut, the swift burst alert telescope (bat) triggered and located grb 210104a (trigger=1015873). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 103.705, +64.661 which is ra(j2000) = 06h 54m 49s dec(j2000) = +64d 39' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 40 sec. the peak count rate was ~16000 counts/sec (15-350 kev), at ~21 sec after the trigger. the xrt began observing the field at 11:28:01.8 ut, 62.7 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 103.7707, 64.6743 which is equivalent to: ra(j2000) = 06h 55m 4.97s dec(j2000) = +64d 40' 27.5" with an uncertainty of 5.3 arcseconds (radius, 90% containment). this location is 111 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 1.41e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of nominal 150.0 seconds with the white filter starting 70 seconds after the bat trigger. there is a candidate afterglow in the list of sources generated on-board at ra(j2000) = 06:55:05.25 = 103.77188 dec(j2000) = +64:40:34.0 = 64.67611 with a 90%-confidence error radius of about 1.10 arc sec. this position is 6.7 arc sec. from the center of the xrt error circle. the estimated magnitude is 15.52. no correction has been made for the expected extinction corresponding to e(b-v) of 0.04. 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 210104a: swift detection of a burst with a bright optical counterpart |
on june 25-29, 2020, during its second sky survey, srg/erosita discovered a new x-ray source srge j195057.5+672122 at ra=19:50:57.5 dec=67:21:21.5 (j2000) with a 95% error radius of 4.1 arcsec. | x-ray and optical transient srge j195057.5+672122: a possible nearby grb afterglow/hypernova |
at 03:53:57 ut, the swift burst alert telescope (bat) triggered and located grb 210306a (trigger=1035994). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 129.965, +60.196 which is ra(j2000) = 08h 39m 52s dec(j2000) = +60d 11' 46" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve shows multiple peaks in a complex structure with a duration of about 15 sec. the peak count rate was ~20,000 counts/sec (15-350 kev), at ~7 sec after the trigger. the xrt began observing the field at 03:55:12.07 ut, 74.9 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with a position: ra, dec 129.96204, 60.203271 which is equivalent to: ra(j2000) = 08h 39m 50.89s dec(j2000) = +60d 12' 11.7" with an uncertainty of 4.7 arcseconds (radius, 90% containment). this location is 27 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. uvot took a finding chart exposure of 150 seconds with the white filter starting 85 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 08:39:49.95 = 129.95813 dec(j2000) = +60:12:19.4 = 60.20538 with a 90%-confidence error radius of about 0.61 arc sec. this position is 13.6 arc sec. from the center of the xrt error circle. the estimated magnitude is 16.22 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.052. burst advocate for this burst is v. d'elia (delia at ssdc.asi.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 210306a: swift detection of a burst with a bright optical counterpart |
we investigate the expected radio emission from short grbs, guided by the observed distributions of their afterglow parameters. our motivation is to explore the radio signatures of the forward and reverse shock in a sgrb jet, as well as the off-axis jet component and radio emission from the dynamical ejecta. we estimate the fraction of grbs detectable in the radio that may be coincident with a gw signal from a neutron star (ns) merger. at the distance to which aligo at design specification is sensitive to gws from ns mergers, we may detect up to 20 % of off-axis jet radio components of these events, and up to about 10 % of events with radio emission from the tidal ejecta shocking with the external medium. we discuss our results in light of the next generation very large array, expected to make significant progress in detecting radio signals from sgrbs. | science with an ngvla: radio emission from short gamma-ray bursts in the multi-messenger era |
we report on the first open-use based atacama large millimeter/submm array (alma) 345 ghz observation for the late afterglow phase of grb 131030a. the alma observation constrained a deep limit at 17.1 d for the afterglow and host galaxy. we also identified a faint submillimeter source (alma j2300-0522) near the grb 131030a position. the deep limit at 345 ghz and multifrequency observations obtained using swift and ratir yielded forward-shock modeling with a two-dimensional relativistic hydrodynamic jet simulation and described x-ray excess in the afterglow. the excess was inconsistent with the synchrotron self-inverse compton radiation from the forward shock. the host galaxy of grb 131030a and optical counterpart of alma j2300-0522 were also identified in the subaru image. based on the deep alma limit for the host galaxy, the 3σ upper limits of ir luminosity and the star formation rate (sfr) are estimated as lir < 1.11 × 1011 l⊙ and sfr <18.7 (m⊙ yr-1), respectively. although the separation angle from the burst location (3{^''.}5) was rather large, alma j2300-0522 may be one component of the grb 131030a host galaxy, according to previous host galaxy cases. | alma and ratir observations of grb 131030a |
we present design status of the microchannel x-ray telescope, the focussing x-ray telescope on board the sino- french svom mission dedicated to gamma-ray bursts. its optical design is based on square micro-pore optics (mpos) in a lobster-eye configuration. the optics will be coupled to a low-noise pnccd sensitive in the 0.2{10 kev energy range. with an expected point spread function of 4.5 arcmin (fwhm) and an estimated sensitivity adequate to detect all the afterglows of the svom grbs, mxt will be able to provide error boxes smaller than 60 (90% c.l.) arc sec after five minutes of observation. | the microchannel x-ray telescope status |
the galactic magnetar sgr 1935+2154 is currently known to be in an active state and has shown flaring activity in the x-ray bands in recent past (palmer et al., atel #13675; younes et al., atel #13678; barthelmy et al., gcn #27657; nakahira et al., gcn #27661). | a ugmrt search for low-frequency persistent radio emission and afterglow from sgr 1935+2154 |
as the central engine of gamma-ray bursts (grbs), a nascent magnetar can release its rotational energy by magnetic dipole radiation. this energy is injected into the outflow of the grb jet. with the rapid evolution of the magnetic inclination angle, the perpendicular component of the magnetar's surface magnetic field decreases rapidly. the energy loss rate of the magnetar is characterized by two different timescales. this peculiar two-stage energy injection model will affect the shape of the x-ray afterglow light curve. it is shown that a new shallow decay phase will emerge following the initial shallow decay phase. as a result, there could be two plateaus in the x-ray light curve. the effects of various physical parameters on the light curves are studied in detail. it is found that the observed afterglows of grb 161217a and grb 190114a, both having two plateaus in the light curve, can be well fitted in our framework. | two x-ray plateaus of gamma-ray bursts: energy injection from nascent magnetars with an evolving magnetic inclination angle |
the chandra x-ray observatory re-observed the field of gw170817 starting on may 3rd, 2018 as part of its on-going monitoring program (pi: wilkes). observations were split into two exposures of 50.7 ks and 46 ks, respectively. | chandra observations of gw170817 reveal a fading afterglow |
the neutron-rich matter ejected by compact object mergers (neutron star-neutron star merger and neutron star-black hole merger) provides one of the most important environments for the syntheses of r-process elements. in recent seventeen years, theoretical studies suggested that the energy produced during the decay of r-process elements will form optical/near infrared (nir) radiations after thermalization. this type of optical/nir transients are called li-paczyński novae, or lp-novae for short. since the typical peak brightness of lp-novae is ∼1000 times brighter than that of a typical nova, they are also called kilonovae. besides, both theoretical and observational studies have showed, directly or indirectly, that under certain conditions, the compact object mergers can produce the gamma-ray bursts with a rather short duration of t90 ≤ 2s (sgrbs for short), and most sgrbs may come from compact object mergers. after the identification of sgrb afterglows, dedicated searches of the lp-novae associated with sgrbs have been taken. in this review we present the theoretical progress of lp-novae in recent seventeen years, and the observational aspect will appear in a upcoming paper. | research developments in li-paczyński novae (i): theoretical aspect |
we obtained spectroscopic observations of the optical counterpart (izzo et al., gcn #29066, jelinek et al., gcn #29070) of the magic-detected (blanch et al., gcn #29075) grb 201216c (beardmore et al., gcn #29061, malacaria et al., gcn #29073, nadella et al., gcn #29074) with the eso very large telescope ut 3 (melipal) equipped with the x-shooter spectrograph, covering the wavelength range 3200-22000 aa. observations started at 01:30 ut on 2020-12-17, 2.38 hr after the burst, and consisted of 4 exposures of 600 s each. the afterglow is well-detected in the stacked spectrum, but the continuum is very red. as a consequence, the s/n drops dramatically from the red to the blue end. we identify a doublet which we tentatively match to ca ii h & k at z = 1.10. unfortunately, no other lines are detected to confirm this value, though most of them would fall in a spectral region of poor s/n. we note that ca ii h&k absorption is uncommon in intervening absorbers, making it likely this is the actual redshift of the grb, and that it does not lie at an even greater distance (in accordance with the vhe detection). a redshift of z = 1.1 would place this object among the most distant known vhe sources. using the fermi gbm parameters (malacaria et al., gcn #29073), we derive a an observer-frame 10-1000 kev isotropic energy release of e_iso = (4.71 +/- 0.16) * 10^53 erg. based on our grz photometry (izzo et al., gcn 29066), we measure a spectral slope beta_opt = 4.1 +- 0.2 (fnu propto nu^-beta), which is an unusually red value, suggesting significant extinction. this is confirmed by the optical-to-x-ray spectral index, beta_ox ~ 0.1 which indicates a very low optical/x-ray flux ratio, making this a bona fide dark grb. we acknowledge excellent support from the eso observing staff in paranal, in particular, diego parraguez, bin yang, and zahed wahhaj. | grb 201216c: vlt x-shooter spectroscopy and potential high redshift of a vhe-emitting grb |
gamma-ray burst (grb) optical and x-ray afterglow luminosity is expected to correlate with the grb isotropic equivalent kinetic energy of the outflow in the standard synchrotron model for grb afterglows. previous studies, using prompt grb isotropic equivalent energy (eiso) as a proxy for isotropic equivalent kinetic energy, have generally confirmed a correlation between x-ray and optical afterglow luminosities. assuming that grb afterglow luminosity does not evolve strongly with redshift, we identify a strong malmquist bias in grb optical and x-ray afterglow luminosity data. we show that selection effects dominate the observed eiso-lopt, x correlations, and have likely been underestimated in other studies. the bias is strongest for a subset of optically faint bursts m > 24 at 24 h with z > 2. after removing this optical selection bias, the eiso-lopt, x correlation for long grbs is not statistically significant, but combining both long and short grb luminosity data the correlation is significant. using the median of the eiso and lopt, x distributions, we apply the synchrotron model assuming the same power-law index for short and long grbs, but different microphysical parameter distributions. comparing the ratio of optical and x-ray luminosities, we find tentative evidence that the fraction of post-shock energy in magnetic fields, ɛb, could be systematically higher in short grbs compared to long grbs. | selection biases in the gamma-ray burst eiso - lopt, x correlation. |
in previous papers it was shown that gamma rays with characteristics similar to those of the gamma-ray bursts (grbs) observed by astronomers may arise from suitably shaped nonuniformities in the big bang in a quasi-spherical szekeres (qss) model. the gamma radiation arises by blueshifting the light emitted by hydrogen atoms at the end of the last scattering epoch along preferred directions that exist in qss models. however, the durations of the gamma flashes and of their afterglows implied by the model were much longer than those of the observed grbs. in this paper it is shown that for the gamma-ray flash a duration of correct order results if the blueshifted radiation, on its way to the present observer, passes through another qss region where it is deflected. the angle of deflection changes with time because of the cosmological drift mechanism, so the high-frequency ray will miss the observer after a while. it is shown by explicit numerical calculation that a gamma-ray flash will no longer be visible to the present observer after 10 minutes. | short-lived flashes of gamma radiation in a quasi-spherical szekeres metric |
grb 110709b presented a peculiar three-peak lightcurve; this burst twice triggered the bat detector onboard swift. the two triggers were separated by ∼10 min. in order to explain such an event, we unify into a single description the millisecond (ms) protomagnetar and the collapsar central-engine models. we find that such a scenario could produce grbs with three peaks. one for the ms-protomagnetar stage, a second one for the bh-formation event and a third one for the collapsar phase. we show that the three peaks for grb 110709b originate from different phases of the same collapsing object. we estimate the energies and timescales of the different episodes of this burst using our model and compare with previous results as well as with a reanalysis we perform on the data. we show that not only the light curve, but also the photon index evolution and the delay between the prompt emission and the afterglow of the second central-engine activity phase point toward a model like the one proposed here. we find that, with reasonable assumptions, our model correctly describes the activity in grb 110709b. we further suggest careful study of future grbs lightcurves which may help show the validity of our model. if our model is correct, this would be the first time that the formation of a bh from a core-collapse event is observed unimpededly. | three-peak grbs and their implications for central engines |
thanks to the advances in robotic telescopes, time domain astronomy leads to a large number of transient events detected in images every night. data mining and machine learning tools used for object classification are presented. the goal is to automatically classify transient events for both further follow-up by a larger telescope and for statistical studies of transient events. special attention is given to the identification of gamma-ray burst afterglows. machine learning techniques are used to identify grond gamma-ray burst afterglow among the astrophysical objects present in the sdss archival images based on the g'-r', r'-i' and i'-z' color indices. the performance of the support vector machine, random forest and neural network algorithms is compared. a joint meta-classifier, built on top of the individual classifiers, can identify grb afterglows with the overall accuracy of ≳ 90%. | machine learning search for gamma-ray burst afterglows in optical images |
we use the correlation relation between the energy emitted by the grbs in their prompt phases and the x-ray afterglow fluxes, in an effort to constrain cosmological parameters and aiming to construct a hubble diagram at high redshifts, i.e. beyond those found with type ia supernovae. | determination of cosmological parameters from gamma ray burst characteristics and afterglow correlations |
we observed the position of grb 201015a (d'elia et al., gcn 28632) with the chandra x-ray observatory with epochs 8.4 and 13.6 days after trigger. the x-ray afterglow is clearly detected with a flux around 100x brighter than expected based on the extrapolation of the early xrt data taken between 0.03 and 0.8 days after burst. the source is seen to fade between the two chandra epochs with a power-law index of approximately -0.8. a swift too has been approved. | grb 201015a: late x-ray detections with chandra |
using the data set from t-239 to t+963 sec from the recent telemetry downlink, we report further analysis of bat grb 201015a (trigger #1000452) (d'elia et al., gcn circ. 28632). the bat ground-calculated position is ra, dec = 354.310, 53.446 deg which is ra(j2000) = 23h 37m 14.4s dec(j2000) = +53d 26' 45.0" with an uncertainty of 2.9 arcmin, (radius, sys+stat, 90% containment). the partial coding was 30%. the mask-weighted light curve shows a short-soft structure with several overlapping pulses that start at ~t0 and end at ~t+1 s, followed by a weak-soft tail that lasts till ~t+10 s. t90 (15-350 kev) is 9.78 +- 3.47 sec (estimated error including systematics). the time-averaged spectrum from t+0.02 to t+10.35 sec is best fit by a simple power-law model. the power law index of the time-averaged spectrum is 3.03 +- 0.68. the fluence in the 15-150 kev band is 2.0 +- 0.6 x 10^-7 erg/cm2. the 1-sec peak photon flux measured from t+0.08 sec in the 15-150 kev band is 1.8 +- 0.4 ph/cm2/sec. all the quoted errors are at the 90% confidence level. the bat spectrum of this event does not appear to be a short hard burst. however, the quickly fading x-ray and optical afterglows are consistent with those from a short grb. if this is a short grb, this is one of the softest short bursts detected by bat (based on a sample with constrained spectral fits from the 3rd bat grb catalog; lien & sakamoto et al. 2016). other bat-detected short grbs with similar softness include grb190326a and grb140622a. grb190326a has an ambiguous origin due to an observing constraint, but late time xrt/uvot followup observations suggest that the source is more consistent with a grb (sbarufatti et al., gcn circ. 24129). grb140622a was classified to be a short grb because the xrt light curve is consistent with the normal behavior of a short burst (sakamoto et al. gcn circ. 16438; burrows et al. gcn circ. 16439). the results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/1000452/ba/ | grb 201015a: swift-bat refined analysis (a soft short pulse with a tail emission) |
here we give an overview of the follow-up campaign of the gamma-ray bursts. and then we give an introduction about gwac project which is aiming to detect the prompt emission with high-cadence photometry and large field of view monitoring. besides, we also present our plan to search for the associated counterparts of gravitational wave events in the optical during the o3 run. | the observations of grb afterglows and the plan to search for optical counterparts of gravitational wave events |
if all long gamma-ray bursts (grbs) are related to supernovae core-collapse supernovae (sne) explosions indeed, then a long grb is the collapse of a massive star core or the beginning of an axially symmetric explosion of sn, and the long grbs must always be accompanied by an sn explosion (of ib/c type or other types of core-collapse sne). then the total energy release of a burst source in gamma rays is in any case not higher that the total electromagnetic energy radiated by the sn (< or ~ 10^(49) erg). within the context of the model of asymmetric explosion of such sne it is discussed when the relation grb-sn is observed and when it is not observed. the accumulated statistics of grb + sn coincidences will confirm the grb compact model more and more. and we tell about the study of grbs in sao ras, about optical identification of the first ten of grbs. | the core collapse supernovae, gamma-ray bursts and sn 1987a |
it is shown that the basic observed properties of the gamma-ray bursts (grbs) are accounted for if one assumes that the grbs arise by blueshifting the emission radiation of hydrogen and helium generated during the last scattering epoch. the blueshift generator for a single grb is a region with a nonconstant bang-time function tb(r ) (described by a lemaître-tolman (l-t) exact solution of einstein's equations) matched into a homogeneous and isotropic (friedmann) background. blueshift visible to the present observer arises only on those rays that are emitted radially in an l-t region. the paper presents three l-t models with different big bang profiles, adapted for the highest and the lowest end of the grb frequency range. the models account for (1) the observed frequency range of the grbs; (2) their limited duration; (3) the afterglows; (4) their hypothetical collimation into narrow jets; (5) the large distances to their sources; (6) the multitude of the observed grbs. properties (2), (3) and (6) are accounted for only qualitatively. with a small correction of the parameters of the model, the implied perturbations of the cmb radiation will be consistent with those actually caused by the grbs. a complete model of the universe would consist of many l-t regions with different tb(r ) profiles, matched into the same friedmann background. this paper is meant to be an initial exploration of the possibilities offered by models of this kind; the actual fitting of all parameters to observational results requires fine-tuning of several interconnected variables and is left for a separate study. | cosmological blueshifting may explain the gamma ray bursts |
global robotic net (lipunov et al., 2010, advances in astronomy,vol.2010, 30l) observed extremaly bright (3.7062e-04 erg/cm^2, ttrig=2019-05-30 10:19:08.9ut, bissaldi et al. gcn #24692) (gbm team gcn #24676, balrog biltzinger et al.gcn #24677, lat longo et al. gcn #24679 and ipn localization; gamma-ray transient also detected by agile 8s later lecarelli et al. gcn #24678, verrecchia et al. gcn #24683) by master-amur, master-tunka, master-saao, master-kislovodsk, master-tavrida, master-iac (lipunov et al. gcn #24680, gcn #24693). | master ot j080207.73+352847.7 discovery - optical afterglow of very bright grb190530a |
we examine the expected radio emission from short grbs detectable by the ngvla, guided by the observed distributions of their afterglow parameters. we give estimates for the peak emission from both the forward and reverse shock, as well as the late-time off-axis jet emission. in the context of neutron star merger model for short grbs, we also estimate the radio emission from the dynamical ejecta of these double neutron star systems. the latter two quasi-spherical radio emission components are particularly important given the advent of gravitational wave (gw) detections of binary compact object mergers. we discuss how the ngvla has potential to shed light on the physics behind short grbs, and estimate the fraction of grbs detectable in the radio that may be coincident with a gw signal from a neutron star (ns) merger. | radio emission from short gamma-ray bursts in the multi-messenger era |
we report the optical observations of grb 121011a by the 0.8m tnt facility at xinglong observatory, china. the light curve of the optical afterglow shows a smooth and featureless bump during the epoch of ∼130 s and ∼5000 s with a rising index of 1.57 ± 0.28 before the break time of 539 ± 44 s, and a decaying index of about 1.29 ± 0.07 up to the end of our observations. moreover, the x-ray light curve decays in a single power-law with a slope of about 1.51 ± 0.03 observed by xrt onboard swift from 100 s to about 10 000 s after the burst trigger. the featureless optical light curve could be understood as an onset process under the external-shock model. the typical frequency has been below or near the optical one before the deceleration time, and the cooling frequency is located between the optical and x-ray wavelengths. the external medium density has a transition from a mixed stage of ism and wind-type medium before the peak time to the ism at the later phase. the joint-analysis of x-ray and optical light curves shows that the emissions from both frequencies are consistent with the prediction of the standard afterglow model without any energy injections, indicating that the central engine has stopped its activity and does not restart anymore after the prompt phase. | optical light curve of grb 121011a: a textbook for the onset of grb afterglow in a mixture of ism and wind-type medium |
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 work showed that grb 091127 gave strong evidence for a double power-law hard electron energy (dplh) spectrum with 1 < p 1 < 2, p 2 > 2 and an “injection break” assumed as γ b ∝ γqin the highly relativistic regime, where γ is the bulk lorentz factor of the jet. in this paper, we show that grb 060614 and grb 060908 provide further evidence for such a dplh spectrum. we interpret the multiband afterglow of grb 060614 with the dplh model in a homogeneous interstellar medium by taking into account a continuous energy injection process, while, for grb 060908, a wind-like circumburst density profile is used. the two bursts, along with grb 091127, suggest a similar behavior in the evolution of the injection break, with q ∼ 0.5. whether this represents a universal law of the injection break remains uncertain and more afterglow observations such as these are needed to test this conjecture. | modeling the multiband afterglows of grb 060614 and grb 060908: further evidence for a double power-law hard electron energy spectrum |
extragalactic x-ray absorption and optical extinction are often found in gamma-ray burst (grb) afterglows, and they could be tracers of both circumburst and host galaxy environments. by performing spectral analyses of the spectral energy distribution of nine short grb (sgrb) afterglows with a known redshift, we investigated the ratio of the equivalent hydrogen column density to the dust extinction, n_h^rest/av^rest, in the rest frame of each sgrb. we found that the distribution of n_h^rest/av^rest is systematically smaller than for long grbs, and is roughly consistent with the gas-to-dust ratio in the milky way. this result means that the measured gas-to-dust ratio of sgrbs would originate from the interstellar medium in each host galaxy. this scenario supports the prediction that sgrbs occur in non-star-forming regions in the host galaxies. | systematic study for gas-to-dust ratio of short gamma-ray burst afterglows |
observations of gamma-ray burst (grb) afterglows have long provided the most detailed information about the origin of this spectacular phenomenon. the model that is most commonly used to extract physical properties of the event from the observations is the relativistic fireball model, where ejected material moving at relativistic speeds creates a shock wave when it interacts with the surrounding medium. electrons are accelerated in the shock wave, generating the observed synchrotron emission through interactions with the magnetic field in the downstream medium. it is usually assumed that the accelerated electrons follow a simple power-law distribution in energy between specific energy boundaries, and that no electron exists outside these boundaries. this letter explores the consequences of adding a low-energy power-law segment to the electron distribution with energy that contributes insignificantly to the total energy budget of the distribution. the low-energy electrons have a significant impact on the radio emission, providing synchrotron absorption and emission at these long wavelengths. shorter wavelengths are affected through the normalization of the distribution. the new model is used to analyze the light curves of grb 990510, and the resulting parameters are compared to a model without the extra electrons. the quality of the fit and the best-fit parameters are significantly affected by the additional model component. the new component is in one case found to strongly affect the x-ray light curves, showing how changes to the model at radio frequencies can affect light curves at other frequencies through changes in best-fit model parameters. | low-energy electrons in gamma-ray burst afterglow models |
the afterglow of a gamma-ray burst (grb) can give us valuable insight into the properties of its host galaxy. to correctly interpret the spectra of the afterglow we need to have a good understanding of the foreground interstellar medium (ism) in our own galaxy. the common practice to correct for the foreground is to use neutral hydrogen (h i) data from the leiden/argentina/bonn (lab) survey. however, the poor spatial resolution of the single dish data may have a significant effect on the derived column densities. to investigate this, we present new high-resolution h i observations with the australia telescope compact array (atca) towards four grbs. we combine the interferometric atca data with single dish data from the galactic all sky survey (gass) and derive new galactic h i column densities towards the grbs. we use these new foreground column densities to fit the swift xrt x-ray spectra and calculate new intrinsic hydrogen column density values for the grb host galaxies. we find that the new atca data show higher galactic h i column densities compared to the previous single dish data, which results in lower intrinsic column densities for the hosts. we investigate the line-of-sight optical depth near the grbs and find that it may not be negligible towards one of the grbs, which indicates that the intrinsic hydrogen column density of its host galaxy may be even lower. in addition, we compare our results to column densities derived from far-infrared data and find a reasonable agreement with the h i data. | exploring the pattern of the galactic h i foreground of grbs with the atca |
this paper is written in occasion of the marcel grossmann award i received at the 13th marcel grossmann meeting held in stockholm in 2012 july 2-7. i review the story of the bepposax discovery of the gamma ray burst afterglow and cosmological distance determination, starting from the first grb detection with vela satellites and from the efforts done before bepposax. an extended review of this story has also been given,1 on the occasion of the award of the fermi prize 2010. | grb afterglow discovery with bepposax: its story 15 years later |
we discuss two historical afterglows (grb 920723 and 920925c) prior to the afterglow era that started in 1997. we show how the use of both the 6-meter bta in zelenchuk (russia) and 10.4-m gtc in la palma (spain) have benefited the study of grb afterglows and their host galaxies. moreover, when completed with our bootes global network of 0.6-meter robotic telescopes, this result had completed studying the early phases starting seconds after the trigger. | gamma-ray bursts: historical afterglows and early-time observations |
it has been reported that some x-ray spectra of gamma-ray burst (grb) afterglows cannot be fitted by a simple power law. a blackbody component is added to precisely fit the thermal feature in these spectra. alternatively, we propose that bremsstrahlung radiation can also be one possible mechanism to explain the thermal component of the grb x-ray afterglow. in particular, we examine the x-ray afterglow of the ultra-long grb 130925a in this paper. by our calculation, we find that the x-ray thermal component observed by both swift-xrt and nustar can be well explained by the bremsstrahlung radiation. our results indicate that the grbs with the bremsstrahlung emission in the x-ray afterglow could be born in a metal-rich and dusty environment. | is bremsstrahlung a possible mechanism to explain the thermal feature in the grb 130925a x-ray afterglow? |
the relativistic external shock model of gamma-ray burst (grb) afterglows has been established with five free parameters, i.e., the total kinetic energy e, the equipartition parameters for electrons {{ɛ }}{{e}} and for the magnetic field {{ɛ }}{{b}}, the number density of the environment n and the index of the power-law distribution of shocked electrons p. a lot of modified models have been constructed to consider the variety of grb afterglows, such as: the wind medium environment by letting n change with radius, the energy injection model by letting kinetic energy change with time and so on. in this paper, by assuming all four parameters (except p) change with time, we obtain a set of formulas for the dynamics and radiation, which can be used as a reference for modeling grb afterglows. some interesting results are obtained. for example, in some spectral segments, the radiated flux density does not depend on the number density or the profile of the environment. as an application, through modeling the afterglow of grb 060607a, we find that it can be interpreted in the framework of the time dependent parameter model within a reasonable range. | revisiting gamma-ray burst afterglows with time-dependent parameters |
we develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered mev-tev photons. for gamma-ray burst (grb) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the gev photons. the number of pairs formed is set by the source gev output (calculated from the fermi-lat fluence), the unknown source lorentz factor, and the unmeasured peak energy of the lat spectral component. we show synchrotron and inverse-compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of grb optical counterparts. pairs formed in bright lat afterglows with a lorentz factor in the few hundreds may produce bright optical counterparts (r\lt 10) lasting for up to one hundred seconds. the number of internal pairs formed from unscattered seed photons decreases very strongly with the source lorentz factor, thus bright grb optical counterparts cannot arise from internal pairs if the afterglow lorentz factor is above several hundreds. | optical flashes from internal pairs formed in gamma-ray burst afterglows |
the rebrightening phenomenon is an interesting feature in some x-ray, optical, and radio afterglows of gamma-ray bursts (grbs). here, we propose a possible energy-supply assumption to explain the rebrightenings of radio afterglows, in which the central engine with multiple active phases can supply at least two grb pulses in a typical grb duration time. considering the case of double pulses supplied by the central engine, the double pulses have separate physical parameters, except for the number density of the surrounding interstellar medium (ism). their independent radio afterglows are integrated by the ground detectors to form the rebrightening phenomenon. in this letter, we firstly simulate diverse rebrightening light curves under consideration of different and independent physical parameters. using this assumption, we also give our best fit to the radio afterglow of grb 970508 at three frequencies of 1.43, 4.86, and 8.46 ghz. we suggest that the central engine may be active continuously at a timescale longer than that of a typical grb duration time as many authors have suggested (e.g., zhang et al., astrophys. j. 787:66, 2014; gao and mészáros, astrophys. j. 802:90, 2015), and that it may supply enough energy to cause the long-lasting rebrightenings observed in some grb afterglows. | radio afterglow rebrightening: evidence for multiple active phases in gamma-ray burst central engines |
the class of long gamma-ray bursts (lgrbs) is associated with the collapse of the most massive stars, making them a tool to investigate star formation in the early universe. furthermore, thanks to their exceptional brightness, lgrb afterglows can be used as extra-galactic background sources capable of unveiling the properties of the cold/warm gas of their hosting galaxies, up to the highest redshifts. therefore lgrbs allow, uniquely, the combination of the information on different phases of the gas, through the absorption lines present in the afterglow spectra and the emission (continuum and lines) properties obtained from host galaxy photometry and spectroscopy, once the afterglow disappeared. to date, the main problem to carry out this kind of studies at very high redshift is the poor number of grbs detected at z>5. the theseus mission will hugely increase such number, as it is expected to detect >100 grbs at z>5. therefore, theseus will bring a unique and fundamental contribution to the understanding of the chemical enrichment of the universe and of the evolution of galaxies and star formation up to the highest redshift. | gamma-ray bursts as tracers of star-formation rate and metallicity evolution with theseus |
galactic foreground hydrogen column density was estimated from hi 21cm surveys, the planck all-sky and akari all-sky data in the direction of the long gamma-ray burst grb 051022, a member of the large grb ring. intrinsic hydrogen column densities were derived from fitting the x-ray afterglow spectrum using all the various foreground estimates. the resolution of the akari fis maps is better than other available all sky survey data on the galactic ism. we show, how much that resolution gain matters calculating the actual foreground column densities, and then deriving an intrinsic column density. | gamma-ray burst parameters and the fine structure of the galactic ism as seen by akari |
we present a method to estimate the jet opening angles of long duration gamma-ray bursts (grbs) using the prompt gamma-ray energetics and 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 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 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. | estimating long grb jet opening angles and rest-frame energetics |
our understanding of gamma-ray bursts (grbs) has come a long way in the past fifty years since their first detection. we now know that grbs arise in distant galaxies and that there are at least two distinct sub-classes, the long-duration class being produced by some rare massive star core collapse and the short-duration class likely by compact binary mergers involved neutron stars. in both cases, the final remnant will be a stellar-mass black-hole or a massive neutron star. the bursts themselves are associated with ultra-relativistic jetted outflows created by these events, and their afterglows by the impact of these outflows on the surrounding circumburst material. increasingly grbs are also being used as probes of the universe, both for understanding galaxy evolution back to the era of reionization, and for the physics of gravitational wave sources. however, many aspects of grbs remain poorly understood, some pointers to which are given here. | gamma-ray bursts progress and problems |
the rapid infrared imager/spectrograph (rimas) is an instrument designed to observe gamma ray burst afterglows following initial detection by the swift satellite. operating in the near infrared between 0.9 and 2.4 μm, it has capabilities for both low resolution (r 25) and moderate resolution (r 4000) spectroscopy. two zinc selenide (znse) grisms provide dispersion in the moderate resolution mode: one covers the y and j bands and the other covers the h and k. each has a clear aperture of 44 mm. the yj grism has a blaze angle of 49.9° with a 40 μm groove spacing. the hk grism is blazed at 43.1° with a 50 μm grooves spacing. previous fabrication of znse grisms on the precision engineering research lathe (perl ii) at llnl has demonstrated the importance of surface preparation, tool and fixture design, tight thermal control, and backup power sources for the machine. the biggest challenges in machining the rimas grisms are the large grooved area, which indicates long machining time, and the relatively steep blaze angle, which means that the grism wavefront error is much more sensitive to lathe metrology errors. mitigating techniques are described. | technique for diamond machining large znse grisms for the rapid infrared/imager spectrograph (rimas) |
we propose to substantially expand our capabilities of modeling relativistic flows of magnetized plasma by merging the uahuntsville-developed multi-scale fluid-kinetic simulation suite and the advanced relativistic mhd (rmhd) code mrgenesis developed in the university of valencia. combined, these will allow us to perform adaptive-mesh-refinement (amr) simulations of discontinuous relativistic flows ubiquitous in the universe. the code developed with this approach will allow us to address problems like the dynamical evolution of magnetized ultra-relativistic outflows that give rise to afterglows of gamma ray bursts (grb). the solution of this problem will substantially benefit on the code's amr capability. | a new rmhd code for astrophysical applications |
the rapid infrared imager-spectrometer (rimas) is a near-infrared (nir) imager and spectrometer that will quickly follow up gamma-ray burst afterglows on the 4.3-meter discovery channel telescope (dct). rimas has two optical arms which allows simultaneous coverage over two bandpasses (yj and hk) in either imaging or spectroscopy mode. rimas utilizes two teledyne hgcdte h2rg detectors controlled by astronomical research cameras, inc. (arc/leach) drivers. we report the laboratory characterization of rimas's detectors: conversion gain, read noise, linearity, saturation, dynamic range, and dark current. we also present rimas's instrument efficiency from atmospheric transmission models and optics data (both telescope and instrument) in all three observing modes. | h2rg detector characterization for rimas and instrument efficiencies |
transcontinental e-vlbi observations were conducted in june 2008 with telescopes in australia, china and japan. detections were made of the radio-loud quasar pks b0727-115, which shows superluminal motion, and the intra-day variable quasar pks b0524+034. the latter source was used as a phase reference calibrator for observations at the position of the gamma-ray burst grb 080409, for which an upper limit to the radio emission is set. australia telescope compact array data were also used to derive a limit on the radio flux density of the grb afterglow. these observations demonstrate the capability to form a large australasian radio telescope network for e-vlbi, with data transported and processed in realtime over high capacity networks. this campaign represents the first step towards more regular e-vlbi observations in this region. | e-vlbi observations of grb 080409 afterglow with an australasian radio telescope network |
in these proceedings, we summarise the exploration so far of the relationship between the afterglow luminosity (measured at rest frame 200s; log l 200 s ) and average afterglow decay rate (measured from rest frame 200s onwards, α > 200 s ) of long duration gamma-ray bursts (grbs), first reported in the optical/uv light curves of grb afterglows. we show that this correlation is also present in the x-ray afterglows of grbs as observed by swift-xrt. we explore how the parameters of the correlation observed in both the x-ray and optical/uv light curves relate to each other and the prompt emission phase and whether these correlations are consistent with predictions of the standard afterglow model. we find that the observed correlations are consistent with a common underlying physical mechanism producing grbs and their afterglows regardless of the detailed temporal behaviour. however, a basic afterglow model has difficulty explaining all the observed correlations. this leads us to briefly discuss alternative more complex models. | exploring the behaviour of long gamma-ray bursts with intrinsic afterglow correlations: log l200s‑α>200s |
while the afterglow phase of gamma-ray bursts (grbs) has been extensively measured, detections of prompt emission (i.e. during bright x-gamma emission) are more limited. some prompt optical measurements are regularly made, but these are typically in a single wide band, with limited time resolution, and no measurement of spectral shape. some models predict a synchrotron self-absorption spectral break somewhere in the ir-optical region. measurement of the absorption frequency would give extensive information on each burst, including the electron lorentz factor, the radius of emission, and more (shen & zhang 2008). thus far the best prompt observations have been explained invoking a variety of models, but often with a non-unique interpretation. to understand this apparently heterogeneous behavior, and to reduce the number of possible models, it is critical to add data on the optical - ir spectral shape.long grb prompt x-gamma emission typically lasts ~40-80 s. the swift bat instrument rapidly measures grb positions to within a few arc minutes and communicates them via the internet within a few seconds. we have measured the time for a fast-moving d=700 mm telescope to point and settle to be less than 9 s anywhere on the observable sky. therefore, the majority of prompt optical-ir emission can be measured responding to bat positions with this telescope. in this presentation, we describe our observing and science programs, and give our design for the burst simultaneous three-channel instrument (bsti), which uses dichroics to send eparate bands to 3 cameras. two emccd cameras, give high-time resolution in b and v; a third camera with a hgcdte sensor covers h band, allowing us to study extinguished bursts. for a total exposure time of 10 s, we find a 5 sigma sensitivity of 21.3 and 20.3 mag in b and r for 1" seeing and kitt peak sky brightness, much fainter than typical previous prompt detections. we estimate 5 sigma h-band sensitivity for an ir optimized telescope to be ~16.9 mag in 20 s. with three channels broadly separated in wavelength, two separate slopes would be measured, or if present between our bands, the absorption frequency would be determined, a brand-new window into grb physics. | measurement of the shape of the optical-ir spectrum of prompt emission from gamma-ray bursts |
we present and examine a correlation observed in both the optical and x-ray afterglows of long duration swift gamma-ray bursts, between the initial luminosity, measured at rest frame 200s, and average afterglow decay rate. | exploring the behaviour of long gamma-ray bursts with intrinsic afterglow correlations |
we compared the time (or time limit) of onset for optical afterglow emission to the γ-ray variability v in 76 gamma-ray bursts with redshifts. in the subset (25 cases) with the rise evident in the data, we fit the shape of the onset peak as well and compared the rising and decaying indices to v. we did not find any evidence for any patterns between these properties and there is no statistical support for any correlations. this indicates a lack of connection between irregularities of the prompt γ-ray emission and the establishment of the afterglow phase. in the ordinary prompt internal shocks interpretation, this would indicate a lack of relationship between v and the bulk lorentz factor of the event. | a search for correlations between gamma-ray burst variability and afterglow onset |
in this thesis i will test the fireball model for grb afterglows. first, i compare different analysis methods and implementations of the model, using data of the "textbook" afterglow of grb 081121a. afterwards, i apply a model based on hydro-dynamical simulations to a sample of short-duration grb afterglows. finally, i analyze data of the particularly interesting grb 150424a, a short grb with extended emission and a long optical plateau phase. | applying the fireball model to short gamma-ray burst afterglows: methods, jet opening angles and plateau phases |
swift-xrt has performed follow-up observations of the swift/bat-guano-detected burst grb 220710a, collecting 4.4 ks of photon counting (pc) mode data between t0+242.5 ks and t0+287.4 ks. an uncatalogued x-ray source is detected consistent with being within 197 arcsec of the swift/bat-guano position and is above the 2sxps 3-sigma upper limit at this position, and is therefore likely the grb afterglow. the position of this source is ra, dec=221.5668, +20.6576 which is equivalent to: ra (j2000): 14:46:16.03 dec(j2000): +20:39:27.3 with an uncertainty of 8.3 arcsec (radius, 90% confidence). this position is 83 arcsec from the swift/bat-guano position. we cannot determine at the present time whether the source is fading. the results of the xrt-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/too_grbs/00021509/source3.php. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021509. this circular is an official product of the swift-xrt team. | grb 220710a: swift-xrt afterglow detection |
many high-energy astrophysical sources accelerate electrons to relativistic velocities, resulting in broadband emission from synchrotron and other radiation processes. gamma-ray burst afterglow observations provide a unique probe of electron acceleration due to the relativistic nature of their collimated outflows. the peaks in gamma-ray burst radio light curves and spectral energy distributions pin down the characteristic synchrotron frequency related to the minimum lorentz factor of the accelerated electrons, γm. we present a method that constrains the fraction of shock energy that resides in electrons, εe, and the fraction of electrons that is shocked into a power-law energy distribution, ξ. based on a large sample of radio afterglows, we show narrow distributions for εe and γm, largely independent of other physical parameters describing the micro- and macrophysics of these gamma-ray burst jets and their environment. we also put constraints on ξ, which is almost impossible to do with broadband modeling due to its degeneracy with other physical parameters. these results have implications for multi-wavelength modeling of gamma-ray burst afterglows and the derived physical parameters, and for simulations of electron acceleration in relativistic shocks, which is relevant for a large variety of high-energy astrophysical sources. | probing electron acceleration in gamma-ray burst afterglows |
the merger of two compact objects neutron stars or black holes could be accompanied by a sudden, immediate flash of radio emission, according to predictions. can an array of antennas in california help us spot these signals?artists impression of two merging neutron stars producing a gamma-ray burst. [national science foundation/ligo/sonoma state university/a. simonnet]missing signalin recent years, the laser interferometer gravitational-wave observatory(ligo) has opened up a new world with the first detections of gravitational waves from compact-object mergers. in 2017, ligo announced the detection of a pair of neutron stars colliding gw170817 and astronomers around the world rushed to watch the fireworks emitted across the electromagnetic spectrum.in the time that followed, we saw gamma rays from a short-duration burst emitted during the merger itself; an optical/near-infrared kilonova, powered by the radioactive decay of heavy elements formed in the merger; and a long-lived radio, x-ray, and optical afterglow, caused when ejecta from the merger slammed into the surrounding environment and decelerated. one signal was missing, however: prompt radio emission.a prompt challengea nighttime photo of some of the antennas in the owens valley radio observatory long wavelength array. [gregg hallinan]according to models, the merger of two neutron stars should produce an immediate flash of radio emission. unlike belated afterglow radio emission, prompt radio emission should emerge immediately after the merger; models predict that it should arrive within as little as a minute of the gravitational-wave signal.catching this signal could provide us with information about the magnetic environment immediately around the binary, the properties of the intergalactic medium, and more. but its a tricky prospect theres very little lead time between the gravitational-wave detection and the radio signal, and the gravitational-wave source is poorly localized. how can we know where to point, quickly enough to capture the prompt radio emission from a merger?the localization of gw170104 is shown in blue, plotted over the ovra-lwas field of view at the time. the gray area was outside of the arrays field of view. [callister et al. 2019]radio eyes on the skyone approach: all-sky radio monitoring, like that provided by the owens valley radio observatory long wavelength array (ovro-lwa). this array of 288 antennas in california continuously scans the sky overhead, taking 13-s integrations that it stores for 24 hours.this broad coverage and data storage means that even if the alert for a gravitational-wave detection comes hours later, scientists still have access to relevant ovro-lwa data. we just have to get lucky to have the source in the field of view of the antennas something that didnt work out for gw170817, but likely will eventually!a successful nondetectionthe ovro-lwa view of the radio sky (from 27 to 84 mhz) at the time of gw170104. the contours show the localization of the gravitational-wave source. [callister et al. 2019]as a proof of concept, a team of scientists led by thomas callister (california institute of technology) recently used the ovro-lwa to perform a search for prompt radio emission from gw170104, a gravitational-wave event for which the majority of the localization region was within the arrays field of view.callister and collaborators didnt spot a signal but this was expected, since gw170104 was a binary black-hole merger, making it unlikely to produce electromagnetic radiation. the team did find, however, that they were able to place useful constraints on the amount of radio emission the merger could have produced, demonstrating the power of the ovro-lwa for future observations.the ovro-lwa is clearly up to the task of detecting prompt emission from upcoming neutron-star mergers. now well just have to wait and see if it spots something in the third ligo observing run, currently underway!citationa first search for prompt radio emission from a gravitational-wave event, thomas a. callister et al 2019 apjl 877 l39. doi:10.3847/2041-8213/ab2248 | catching radio signals from colliding objects |
swift/bat did not localize grb 220310c onboard (t0: 2022-03-10t22:23:51 utc, fermi/gbm gcn 31735). the fermi notice, distributed in near real-time, triggered the swift mission operations center operated gamma-ray urgent archiver for novel opportunities (guano; tohuvavohu et al. 2020, apj, 900, 1). upon trigger by this notice, guano sent a command to the swift burst alert telescope (bat) to save 200 seconds of bat event-mode data from [-50,+150] seconds around the time of the burst. all the requested event mode data was delivered to the ground. the bat likelihood search, nitrates (delaunay + tohuvavohu, arxiv:2111.01769), detects the burst in a 8.192 s analysis time bin with a sqrt(ts) of 9.7. a candidate arcminute localization is found with deltallhout of 19.7 and a deltallhpeak of 5.7. for this reason we can confidently claim detection, and preference for an in fov origin, but the best fit arcmin localization is not strongly preferred over other positions. a few burst locations with comparable deltallhpeak have been previously verified with afterglow discovery (eg grb 211106a). see section 9.1 and figure 20 in the nitrates paper for brief descriptions and interpretations of sqrt(ts), deltallhpeak, and deltallhout. no source is found with conventional bat imaging. this is expected given the strength of the signal in bat, and its position near the edge of the coded fov. the bat position is ra, dec = 290.069, +40.253 deg which is ra(j2000) = 19h 20m 16.62s dec(j2000) = +40d 15' 12.3″ with an estimated uncertainty of 5 arcmin. this independent position is consistent with the fermi/gbm localization (gcn 31735). xrt and uvot follow-up has been requested. results of follow-up observations will be reported in future circulars. guano is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of bat event mode data around the times of compelling astrophysical events to enable more sensitive grb searches. a live reporting of swift/bat event data recovered by guano can be found at: https://www.swift.psu.edu/guano/ | grb 220310c: swift/bat-guano candidate arcminute localization |
at 23:20:21 ut, the swift burst alert telescope (bat) triggered and located grb 220521a (trigger=1107466). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 275.197, +10.384 which is ra(j2000) = 18h 20m 47s dec(j2000) = +10d 23' 03" 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 15 sec. the peak count rate was ~4000 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 23:21:57.7 ut, 96.3 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source located at ra, dec 275.22891, 10.37262 which is equivalent to: ra(j2000) = 18h 20m 54.94s dec(j2000) = +10d 22' 21.4" with an uncertainty of 3.7 arcseconds (radius, 90% containment). this location is 120 arcseconds from the bat onboard position, within the bat error circle. this position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 1.87 x 10^21 cm^-2 (willingale et al. 2013). 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. results 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 0.185. burst advocate for this burst is s. dichiara (simonedichiara55 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 220521a: swift detection of a burst |
the analysis of 176 grb afterglow plateaus observed by swift with known redshifts revealed that the subsample of long grbs associated with sne (grb-sne), composed of 19 grbs, presents a very high correlation coefficient between luminosity at the end of the plateau phase lx (ta) = la and the end time of the plateau ta*, (hereafter lt correlation). moreover, a category of grbs with spectroscopically associated sne (7 grbs) show a higher lt correlation than any other analyzed sample, but with a steeper slope than the long grbs for which no associated sn has been observed (hereafter grbno-sne, 128 grbs). the difference among the grb-no-sne slope of 128 grbs, and the one of the grb-sne (7 grbs), which we have demonstrated through the efron & petrosian method18 not to be due to grb instrumental selection bias, is statistical significant with p = 0.005. this possibly suggest that the grb-sne might not require a standard energy reservoir in the plateau phase unlike the grb-no-sne. furthermore, these sne ib/c associated with grbs obey also the peak-magnitude stretch relation, similar to the one used to standardize the sne ia. therefore, this analysis may open new perspective in future theoretical investigations of the grbs with plateau emission and associated with sne. | gamma-ray bursts with afterglow plateau phases associated with supernovae |
at 02:28:17 ut, the swift burst alert telescope (bat) triggered and located grb 221110a (trigger=1136936). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 29.119, -27.314 which is ra(j2000) = 01h 56m 29s dec(j2000) = -27d 18' 50" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a single-peaked structure with a duration of about 10 sec. the peak count rate was ~1400 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 02:29:32.8 ut, 75.3 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 29.09928, -27.29435 which is equivalent to: ra(j2000) = 01h 56m 23.83s dec(j2000) = -27d 17' 39.7" with an uncertainty of 3.5 arcseconds (radius, 90% containment). this location is 94 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 (1.46 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 4.2 (+3.14/-2.70) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 150 seconds with the white filter starting 80 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 01:56:23.90 = 29.09958 dec(j2000) = -27:17:36.9 = -27.29355 with a 90%-confidence error radius of about 0.5 arc sec. this position is 3.0 arc sec. from the center of the xrt error circle. the estimated magnitude is 18.62 with a 1-sigma error of about 0.07. burst advocate for this burst is m. a. williams (mjw6837 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 221110a: swift detection of a burst with an optical counterpart |
gamma-ray burst (grb) afterglow emission can be observed from sub-tev to radio wavelengths, though only 6.6% of observed grbs present radio afterglows. we examine grb radio light curves (lcs) to look for the presence of radio plateaus resembling the plateaus observed at x-ray and optical wavelengths. we analyze 404 grbs from the literature with observed radio afterglow and fit 82 grbs with at least five data points with a broken power-law model, requiring four parameters. from these, we find 18 grbs that present a break feature resembling a plateau. we conduct the first multiwavelength study of the dainotti correlation between the luminosity la and the rest-frame time of break ta * for those 18 grbs, concluding that the correlation exists and resembles the corresponding correlation at x-ray and optical wavelengths after correction for evolutionary effects. we compare ta * for the radio sample with ta * values in x-ray and optical data, finding significantly later break times in the radio. we propose that this late break time and the compatibility in slope suggest either a long-lasting plateau or the passage of a spectral break in the radio band. we also correct the distribution of the isotropic energy eiso versus the rest-frame burst duration t * 90 for evolutionary effects and conclude that there is no significant difference between the t* 90 distributions for the radio lcs with a break and for those without | examining two-dimensional luminosity-time correlations for gamma-ray burst radio afterglows with vla and alma |
at 14:48:34 ut, the swift burst alert telescope (bat) triggered and located grb 230216a (trigger=1154815). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 113.966, -8.015 which is ra(j2000) = 07h 35m 52s dec(j2000) = -08d 00' 53" 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 ~700 counts/sec (15-350 kev), at ~0 sec after the trigger. the xrt began observing the field at 14:50:15.1 ut, 100.3 seconds after the bat trigger. using promptly downlinked data we find an uncatalogued x-ray source with an enhanced position: ra, dec 113.95924, -8.01160 which is equivalent to: ra(j2000) = 07h 35m 50.22s dec(j2000) = -08d 00' 41.8" with an uncertainty of 1.9 arcseconds (radius, 90% containment). this location is 27 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 3.17 x 10^21 cm^-2 (willingale et al. 2013). uvot took a finding chart exposure of 150 seconds with the white filter starting 105 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 0.197. the xrt position is 3.8" from the galaxy wisea j073550.15-080045.2 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 230216a: swift detection of a burst |
we observed the field of grb 230815a (klingler et al., gcn 34434; mailyan et al. gcn 34440) with the eso very large telescope, equipped with the hawk-i near-infrared camera. observations consisted of two epochs of 20 min exposure in the h band at 23:19:53 ut on 2023-08-15 (~12.5 hr after trigger) and 23:15:46 ut on 2023-08-16 (~36.4 hr after trigger). in both epochs, we clearly detected two sources consistent with the xrt error circle (beardmore et al., gcn 34437). one of the sources has significantly faded (~2 mag) between the two epochs, evolving from ab mag = 20.11 +/- 0.02 to ab mag = 22.01 +/- 0.08. this corresponds to a power-law decay index of 1.65, similar to the x-ray decay rate, suggesting a small host contribution to the nir flux. the proposed afterglow of the burst is detected at coordinates: ra (j2000) = 12:18:53.24 dec (j2000) = -58:03:09.45 with an uncertainty of 0.3". we acknowledge the excellent support provided by the paranal staff, in particular joe anderson. | grb 230815a: vlt/hawk-i near-infrared afterglow detection |
at 12:53:33 ut, the swift burst alert telescope (bat) triggered and located grb 170629a (trigger=759159). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 130.016, -46.587 which is ra(j2000) = 08h 40m 04s dec(j2000) = -46d 35' 11" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve is incomplete at this time due to lost telemetry, but was still rising at 8 sec after the trigger with a count rate of ~1500 counts/sec. the xrt began observing the field at 12:54:56.0 ut, 82.9 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source located at ra, dec 129.98653, -46.57155 which is equivalent to: ra(j2000) = 08h 39m 56.77s dec(j2000) = -46d 34' 17.6" with an uncertainty of 4.7 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 http://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. no spectrum from the promptly downlinked event data is yet available to determine the column density. the initial flux in the 2.5 s image was 5.16e-10 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 90 seconds with the uvw2 filter starting 86 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. analysis is complicated because of a nearby bright star (b vel). full results will have to await the full dataset. burst advocate for this burst is a. cholden-brown (aaronb at swift.psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/too.html.) | grb 170629a: swift detection of a burst |
at 13:53:15 ut, the swift burst alert telescope (bat) triggered and located grb 220430a (trigger=1104692). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 97.611, +9.510 which is ra(j2000) = 06h 30m 27s dec(j2000) = +09d 30' 36" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve appears to show a double-peaked structure with the second peak larger, and a total duration of about 70 sec. the peak count rate was ~35000 counts/sec (15-350 kev), at ~38 sec after the trigger. however, near the time of the grb the sun also produced an x-class solar flare which may be the cause of some or all of the apparent lightcurve activity. the grb emission will be independently determined once the mask-tagged bat data has been received. the xrt began observing the field at 13:54:07.7 ut, 51.7 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source with an enhanced position: ra, dec 97.61267, 9.54730 which is equivalent to: ra(j2000) = 06h 30m 27.04s dec(j2000) = +09d 32' 50.3" with an uncertainty of 1.9 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 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 (6.47 x 10^21 cm^-2, willingale et al. 2013), with an excess column of 1.1 (+0.75/-0.59) x 10^22 cm^-2 (90% confidence). the initial flux in the 0.1 s image was 4.31e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 60 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the large, but uncertain, extinction expected. although this looks like a grb both in terms of its lightcurve and the presence of strong flux above 100 kev, its location near the galactic plane (lon=202.05, lat=-0.26) raises the possibility of it being a galactic transient. in addition, as noted above, the apparent lightcurve may be due to solar activity. if further analysis shows that it is a galactic transient, we will use the name swift j0630.4+0932. 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 220430a: swift detection of a burst or swift j0630.4+0932 |
recent space- and ground-based studies of the circumgalactic medium (cgm) around nearby galaxies have revealed the dynamic interplay between the galaxy ecosystem and surrounding cgm using bright background quasars. here, we extend this investigation to higher redshifts by using the bright afterglows of gamma-ray bursts (grbs) as background sources probing the cgm of their own host galaxies. we compiled a sample of 27 high-resolution (r > 6000) and high-quality (typical s/n ~ 15) rest-frame uv spectra of grb afterglows in a redshift range (2 < z < 6) obtained using keck-hires, vlt-uves, and vlt-x-shooter spectrographs. we find stronger blue wings in high-ionization species (si iv, c iv) compared to the low-ionization species (si ii, fe ii), indicative of the presence of ubiquitous warm outflows in the grb hosts at high redshifts. we developed a code to simulate the cgm and ism kinematics sampled by a grb sightline. using these kinematic models, we estimated typical values of cgm properties (for the sample) such as cgm mass (109.8 msolar) and outflow launch velocity (300 km/s). further, by comparing our results with previous c iv absorption studies at high and low redshifts, we find a possible cgm-galaxy co-evolution. essentially, over the course of evolution of present-day galaxies with m* > 1010 msolar, the ratio of c iv mass in the cgm to the stellar mass remains fairly uniform, such that log(mciv/m∗)∼(-4.5) within ±0.5 dex from z∼4 to z∼0, suggesting cgm-galaxy co-evolution. this study demonstrates a method ot probe the cgm-galaxy co-evolution, which is an important piece of the galaxy growth puzzle and needs to be explored further in large-scale galaxy simulations. | probing the circumgalactic medium in the early universe using grb afterglows |
with the first discovery of a ns merger detected with gravitational wavefacilities, and ongoing detections of sgrbs detected with gamma-raysatellites, it is a golden era to make significant progress in mergerstudies. a critical link between these populations is the production ofrelativistic jets, and the fraction of mergers that produce relativisticsgrb-like outflows. deep x-ray observations have played an importantrole in constraining the collimation of sgrbs, as our current knowledgeof the opening angle distribution comes almost exclusively from x-rayobservations at >1 day after the burst. here, we propose for xmm-newtontoo observations to monitor a sgrb afterglow and constrain its openingangle, which will have significant implications for the energy scalesand event rates. | xmm-newton observations of jets in short gamma-ray bursts |
long-duration gamma-ray bursts (grbs) are associated with the explosions of massive stars and are accordingly expected to reside in star-forming regions with molecular gas (the fuel for star formation). previous searches for co, a tracer of molecular gas, in grb host galaxies did not detect any emission. molecules have been detected as absorption in the spectra of grb afterglows, but absorption lines probe the interstellar medium only along the line of sight, so it is not clear whether the molecular gas represents the general properties of the regions where the grbs occur.we conducted spatially resolved observations of co line and 1.2-mm continuum emission in two host galaxies of grbs (grb 020819b at z = 0.41 and grb 051022 at z = 0.81) by using the atacama large millimeter/submillimeter array (alma). we observed the redshifted co(3-2) line for the grb 020819b host and the co(4-3) line for the grb 051022 host with the angular resolution of ~1". we detected co line and 1.2-mm continuum emission from the two hosts. this is the first case for detecting molecular gas emission in grb hosts. the co emission is clearly detected at the nuclear region of the grb 020819b host and the grb 051022 host. the spatially resolved continuum map of the grb 020819b host shows that the emission is significantly detected only at a star-forming region ~3" (16 kpc in projection) away from the nuclear region, where the grb explosion occurred. we found that the burst happened in regions rich in dust, but not particularly rich in molecular gas. the ratio of molecular gas mass to dust mass of the grb site is significantly lower than that of the nuclear region, indicating that the grb occurred under particular circumstances within the host. the ratio at the grb site is also lower than those of the milky way and nearby star-forming galaxies, suggesting that the star-forming environment where the grb occur is different from those in local galaxies. the possible reason for the deficit of molecular gas in the grb site is that much of the dense gas is dissipated by a strong interstellar ultraviolet radiation field, which is expected in regions with intense star formation. | gamma-ray bursts from dusty regions with little molecular gas |
we report here the discovery by the intermediate palomar transient factory (iptf) of iptf14yb, the first unambiguous detection of an afterglow-like transient identified outside the γ-ray bandpass. subsequent to our discovery announcement, the ``parent'' γ-ray burst grb 140226a was identified by the interplanetary network of high-energy detectors. we demonstrate an association between iptf14yb and grb 140226a based both on probabilistic arguments and by comparing iptf14yb with the known population of long grb afterglows and host galaxies. we furthermore estimate the rate of iptf14yb-like transients based on iptf observations, and demonstrate it is consistent with the rate of on-axis long grbs. finally, we briefly discuss the implications of the non-detection to date of bona fide ``orphan'' afterglows (i.e., those lacking entirely in high-energy emission) on grb beaming and the degree of baryon loading in these relativistic jets. | iptf14yb: the first grb discovered outside the gamma-ray bandpass and the rate of orphan afterglows |
swift-xrt has performed follow-up observations of the swift/bat-guano-detected burst grb 220708b, collecting 1.7 ks of photon counting (pc) mode data between t0+35.1 ks and t0+36.8 ks. an uncatalogued x-ray source is detected and is above the rass 3-sigma upper limit at this position, and is therefore likely the grb afterglow. the position of this source is ra, dec=248.5790, +36.3478 which is equivalent to: ra (j2000): 16:34:18.97 dec(j2000): +36:20:52.0 with an uncertainty of 4.0 arcsec (radius, 90% confidence). this position is 3.6 arcmin from the swift/bat-guano position. the light curve is consistent with a constant source of mean count rate 6.5e-02 ct/sec. a power-law fit gives an index of 0.0 (+0.0, -3.3). a spectrum formed from the pc mode data can be fitted with an absorbed power-law with a photon spectral index of 2.3 (+0.6, -0.5). the best-fitting absorption column is 3.2 (+2.2, -1.7) x 10^21 cm^-2, in excess of the galactic value of 1.4 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 3.2 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1. a summary of the pc-mode spectrum is thus: total column: 3.2 (+2.2, -1.7) x 10^21 cm^-2 galactic foreground: 1.4 x 10^20 cm^-2 excess significance: 2.9 sigma photon index: 2.3 (+0.6, -0.5) the results of the xrt-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021508. the results of the full analysis of the xrt observations are available at https://www.swift.ac.uk/too_grbs/00021508. this circular is an official product of the swift-xrt team. | grb 220708b: swift-xrt afterglow detection |
at 11:20:23 ut, the swift burst alert telescope (bat) triggered and located grb 200519a (trigger=973140). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 255.334, -30.380 which is ra(j2000) = 17h 01m 20s dec(j2000) = -30d 22' 47" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 80 sec. the peak count rate was ~37000 counts/sec (15-350 kev), at ~23 sec after the trigger. the xrt began observing the field at 11:21:13.3 ut, 49.6 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 255.3327, -30.3782 which is equivalent to: ra(j2000) = 17h 01m 19.85s dec(j2000) = -30d 22' 41.5" with an uncertainty of 4.7 arcseconds (radius, 90% containment). this location is 7.6 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 1.36e-08 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 57 seconds after the bat trigger. there is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at ra(j2000) = 17:01:20.00 = 255.33335 dec(j2000) = -30:22:40.9 = -30.37803 with a 90%-confidence error radius of about 0.61 arc sec. this position is 2.1 arc sec. from the center of the xrt error circle. the estimated magnitude is 15.38 with a 1-sigma error of about 0.14. no correction has been made for the expected extinction corresponding to e(b-v) of 0.47. burst advocate for this burst is b. sbarufatti (bxs60 at psu.edu). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200519a: swift detection of a burst with an optical afterglow |
when two neutron stars merged in august of 2017, telescopes around the world watched the fireworks that came next. but its not just the seconds and minutes after merger that can teach us about what happened! hubble observations of the afterglow a year later are now providing new clues.a wealth of observationslate-time hubble observations of gw170817 spanning 170 days to 358 days after the merger. [adapted from lamb et al. 2019]the discovery of gw170817 the first gravitational-wave detection of a binary-neutron-star merger with an observed electromagnetic counterpart finally promised a close look at what happens when two compact objects merge. following the merger, we gathered observations of the accompanying signals: a weak short-duration gamma-ray burst, a kilonova powered by radioactive decay, and a long-lived afterglow traced in radio, x-ray, and optical wavelengths.two leading questions we hoped gw170817 would answer were how matter is expelled during the sudden explosion of energy when neutron stars collide, and what the environment around the colliding stars is like. now, a team of scientists led by gavin lamb (university of leicester) has used hubble observations from a year post-merger to address these questions.model light curves fit to various observations of gw170817s afterglow, spanning a year after merger. [lamb et al. 2019]structuring a jettwo leading theories for the observed outflow from gw170817 are a jet-dominated model, in which a fast-moving jet punched through the surrounding material and carried away mass and energy, or a cocoon-dominated model, in which a jet tried to escape, but was instead choked by a surrounding cocoon of slow-moving material.the authors analysis of the afterglow observed by hubble indicates that a structured jet did, in fact, appear an outcome that supports previous radio observations also favoring the jet-dominated model.to better understand the structure of the jet, lamb and collaborators model gw170817s outflow in two ways:a two-component jet that consists of a very narrow (only 5 wide), incredibly fast-moving core (flowing at nearly the speed of light!) surrounded by a slower-moving, slightly wider ( 15) cocoon of swept-up material; ora single-component jet with a smooth, gaussian distribution of energy and no cocoon.the authors find that both models well fit the afterglow observed by hubble, though the single-component gaussian model provides a slightly better fit at late times. continued observations may help to distinguish between the models.a cluster home?hubble image of the lenticular galaxy ngc 4993, host to gw170817 (shown over time in the zoomed insets]. could gw170817 have been hosted in a star cluster within this galaxy? [nasa and esa]in addition to exploring the jet, the authors place constraints on the host environment for gw170817.its possible that neutron-star mergers may occur in star clusters, as the high density of stars in clusters could lead to binary pairs. weve identified the host galaxy for gw170817,but we cant directly tell whether the merger occurred within a star cluster in the galaxy.using the hubble observations, however, the authors show that the brightness of any underlying host cluster would have to be extremely low so low, in fact, that it would be dimmer than 99% of local-group globular clusters.we can add these constraints to the pile of intriguing clues we continue to accumulate as we study this landmark event!citationthe optical afterglow of gw170817 at one year post-merger, g. p. lamb et al 2019 apjl 870 l15. doi:10.3847/2041-8213/aaf96b | clues from hubble a year after a neutron-star merger |
at 13:25:33 ut, the swift burst alert telescope (bat) triggered and located grb 180514a (trigger=832368). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 197.401, +36.969 which is ra(j2000) = 13h 09m 36s dec(j2000) = +36d 58' 10" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). the bat light curve showed a multi-peaked structure with a duration of about 40 sec. the peak count rate was ~1300 counts/sec (15-350 kev), at ~5 sec after the trigger. the xrt began observing the field at 13:26:51.3 ut, 77.8 seconds after the bat trigger. using promptly downlinked data we find a bright, uncatalogued x-ray source with an enhanced position: ra, dec 197.3713, 36.9720 which is equivalent to: ra(j2000) = 13h 09m 29.12s dec(j2000) = +36d 58' 19.3" with an uncertainty of 3.6 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 http://www.swift.ac.uk/sper. we cannot determine whether the source is fading at the present time. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the galactic value of 1.18 x 10^20 cm^-2 (willingale et al. 2013). the initial flux in the 2.5 s image was 1.69e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 86 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.6 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.01. the first bat position notice identified this trigger as a transient from a known source because of proximity with the spiral galaxy ngc 5005. however, given the separation between the xrt position and ngc 5005 (~18 arcmin) and the look of the promptly downlinked bat and xrt data we believe this is a grb not associated with the foreground galaxy. burst advocate for this burst is s. j. laporte (extragsam 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/too.html.) | grb 180514a: swift detection of a burst |
swift-xrt has performed follow-up observations of the integral-detected burst grb 200424a (mereghetti et al. gcn circ. 27634), collecting 5.0 ks of photon counting (pc) mode data between t0+13.2 ks and t0+30.7 ks. one uncatalogued x-ray source has been detected consistent with being within the integral position, however 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): 307.5055 = 20:30:01.31 dec (j2000.0): -39.7001 = -39:42:00.5 error: 3.0 arcsec (radius, 90% conf. [enhanced position]) count-rate: (8.3 [+1.7, -1.6])e-3 ct s^-1 distance: 22 arcsec from integral position. flux: (2.68 [+0.55, -0.52])e-13 erg cm^-2 s^-1 (observed, 0.3-10 kev) seven 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/00020989. this circular is an official product of the swift-xrt team. | grb 200424a: swift-xrt observations |
at 13:49:40 ut, the swift burst alert telescope (bat) triggered and located grb 180624a (trigger=844192). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 318.071, -2.332, which is ra(j2000) = 21h 12m 17s dec(j2000) = -02d 19' 55" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). due to missing downlinked realtime data in the light curve, we cannot give the bat light curve description. the xrt began observing the field at 13:51:32.6 ut, 112.2 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 318.0951, -2.3397 which is equivalent to: ra(j2000) = +21h 12m 22.82s dec(j2000) = -02d 20' 22.9" with an uncertainty of 5.2 arcseconds (radius, 90% containment). this location is 91 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 1.93e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 118 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 0.05. burst advocate for this burst is s. l. gibson (slg44 at le.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/too.html.) | grb 180624a: swift detection of a burst |
we report the first constraints on the putative radio emission of srge j195057.5+672122, reported as a possible gamma-ray burst (grb) afterglow/hypernova (sazonov et al. atel #13987) with a fading optical emission (perley, atel #13989; zaznobin et al. atel #13990). | vlass constraints on the radio afterglow of the grb afterglow/hypernova candidate srge j195057.5+672122 |
gamma-ray burst (grb) afterglows have long played a key role in our understanding of the physics of grbs. the recent detection of the electro-magnetic counterparts including an afterglow jet to a neutron star merger indicate that this will remain so in the future. with the detection of grb 170817a, afterglow observations have fully caught up again with theory and we have been provided with an opportunity to discard old jet models, refine alternative jet geometry models already in the literature and to think hard about future predictions. the grb community has admirably stepped up to the plate and observational, theoretical and computational progress has been very rapid over the past years. additionally, large- scale electro-magnetic surveys, observations at extremely high frequencies and an increasing number of gravitational-wave detections of merging neutron stars offer tantalizing prospects of further upheavals in afterglow and grb theory. in these proceedings, i will take stock of some theoretical progress on afterglow theory made in the past few years. | recent developments in gamma-ray afterglow theory |
at 19:24:34 ut, the swift burst alert telescope (bat) triggered and located grb 180510a (trigger=831810). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 276.318, -31.911 which is ra(j2000) = 18h 25m 16s dec(j2000) = -31d 54' 38" 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 70 sec. the peak count rate was ~8000 counts/sec (15-350 kev), at ~5 sec after the trigger. the xrt began observing the field at 19:26:02.5 ut, 88.3 seconds after the bat trigger. xrt found a bright, uncatalogued x-ray source located at ra, dec 276.3303, -31.9069 which is equivalent to: ra(j2000) = +18h 25m 19.27s dec(j2000) = -31d 54' 24.8" with an uncertainty of 5.5 arcseconds (radius, 90% containment). this location is 40 arcseconds from the bat onboard position, within the bat error circle. no event data are yet available to determine the column density using x-ray spectroscopy. the initial flux in the 2.5 s image was 1.09e-09 erg cm^-2 s^-1 (0.2-10 kev). uvot took a finding chart exposure of 150 seconds with the white filter starting 96 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. 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 0.26. 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/too.html.) | grb 180510a: swift detection of a burst |
at 19:38:05 ut, the swift burst alert telescope (bat) triggered and located grb 200729a (trigger=984929). swift slewed immediately to the burst. the bat on-board calculated location is ra, dec 184.375, +45.582 which is ra(j2000) = 12h 17m 30s dec(j2000) = +45d 34' 56" 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 ~500 counts/sec (15-350 kev), at ~10 sec after the trigger. the xrt began observing the field at 19:40:25.5 ut, 140.4 seconds after the bat trigger. using promptly downlinked data we find a fading, uncatalogued x-ray source located at ra, dec 184.37782, 45.59380 which is equivalent to: ra(j2000) = 12h 17m 30.68s dec(j2000) = +45d 35' 37.7" with an uncertainty of 3.5 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. a power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the galactic value (1.07 x 10^20 cm^-2, willingale et al. 2013), with an excess column of 6.5 (+3.87/-3.22) x 10^21 cm^-2 (90% confidence). uvot took a finding chart exposure of 250 seconds with the u filter starting 303 seconds after the bat trigger. no credible afterglow candidate has been found in the initial data products. the 2.7'x2.7' sub-image covers 100% of the xrt error circle. the typical 3-sigma upper limit has been about 19.2 mag. the 8'x8' region for the list of sources generated on-board covers 100% of the xrt error circle. the list of sources is typically complete to about 18.0 mag. no correction has been made for the expected extinction corresponding to e(b-v) of 0.01. the xrt position is within the extent of the nearby galaxy ngc 4242, for which simbad lists a redshift of 0.00176 (~7.4 mpc). follow up observations are strongly encouraged. burst advocate for this burst is p. a. evans (pae9 at star.le.ac.uk). please contact the ba by email if you require additional information regarding swift followup of this burst. in extremely urgent cases, after trying the burst advocate, you can contact the swift pi by phone (see swift too web site for information: http://www.swift.psu.edu/) | grb 200729a: swift detection of a burst |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.