GRB 080916C AND GRB 090510: THE HIGH-ENERGY EMISSION AND THE AFTERGLOW
56
Citation
25
Reference
10
Related Paper
Citation Trend
Abstract:
We constrain the physical composition of the outflows of GRBs 080916C and 090510 with the prompt emission data and find that the former is likely magnetic while the latter may be baryonic. The X-ray and optical afterglow emission of both GRBs can be reasonably fitted using the standard external shock model but the density profiles of the circum-burst medium are different. We also propose a simple method to estimate the number of the seed photons suppose the GeV afterglow photons are due to the inverse Compton radiation of external forward shock electrons. The seed photons needed in the modeling are too many to be realistic for both events. The synchrotron radiation of the forward shock seems able to account for the GeV afterglow data.The successful launch and operation of NASA’s Swift Gamma‐Ray Burst Explorer open a new era for a multi‐wavelength study of the very early afterglow phase of gamma‐ray bursts (GRBs). GRB early afterglow information is very essential to explore the unknown physical composition of GRB jets, the link between the prompt γ‐ray emission and the afterglow emission, the GRB central engine activity, as well as the immediate GRB environment. Here I review some of the recent theoretical efforts to address these problems and describe how the latest Swift data give answers to these outstanding questions.
Swift
Cite
Citations (3)
We report on follow-up observations of 20 short-duration gamma-ray bursts (T90 < 2s) performed in g′r′i′z′JHKs with the Gamma-Ray Burst Optical Near-Infrared Detector (GROND) between mid-2007 and the end of 2010. This is the most homogeneous and comprehensive data set on GRB afterglow observations of short bursts. In three cases, GROND was on target within less than 10 min after the trigger, leading to the discovery of the afterglow of GRB 081226A and its faint underlying host galaxy. In addition, GROND was able to image the optical afterglow and follow the light curve evolution in five further cases: GRBs 090305, 090426, 090510, 090927, and 100117A. Three of the aforementioned six bursts with optical light curves show a break: GRBs 090426 and 090510 as well as GRB 090305. For GRB 090927, no break is seen in the optical/X-ray light curve until about 150 ks/600 ks after the burst. A decay slope of the optical afterglow of GRB 100117A could be measured. Using these data supplemented by about ten events taken from the literature, we compare the jet half-opening angles of long and short bursts. We find a tentative evidence that short bursts have wider opening angles than long bursts. However, the statistics are still very poor and follow-up observations of these events are therefore very important to gain as much observational data as possible.
Cite
Citations (1)
Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Currently, only lower limits were securely set to the initial fireball Lorentz factor Gamma_0. We aim to provide a direct measure of Gamma_0. The early-time afterglow light curve carries information about Gamma_0, which determines the time of the afterglow peak. We have obtained early observations of the near-infrared afterglows of GRB 060418 and GRB 060607A with the REM robotic telescope. For both events, the afterglow peak could be clearly singled out, allowing a firm determination of the fireball Lorentz of Gamma_0 ~ 400, fully confirming the highly relativistic nature of GRB fireballs. The deceleration radius was inferred to be R_dec ~ 10^17 cm. This is much larger than the internal shocks radius (believed to power the prompt emission), thus providing further evidence for a different origin of the prompt and afterglow stages of the GRB.
Cite
Citations (0)
GRBs 050223 and 050911 are examples of Swift bursts with two of the faintest X‐ray afterglows at (relatively) early times. While a faint, fading X‐ray afterglow was located for GRB 050223, GRB 050911 was not detected, making any X‐ray afterglow extremely faint. The faintness of the afterglow of GRB 050223 could be explained by a large opening or viewing angle, or by the burst being at high redshift. The non‐detection of GRB 050911 may indicate the burst occurred in a low‐density environment, or, alternatively, was due to a compact object merger, in spite of the apparent long duration of the burst.
Swift
Cite
Citations (0)
Extensive observational campaigns of afterglow hunting have greatly enriched our understanding of the gamma-ray burst (GRB) phenomenon. Efforts have been made recently to explore some afterglow properties or signatures that will be tested by the on-going or the future observational campaigns yet come. These include the properties of GRB early afterglows in the temporal domain; the GeV-TeV afterglow signatures in the spectral domain; as well as a global view about the GRB universal structured jet configuration. These recent efforts are reviewed. Within the standard cosmological fireball model, the very model(s) responsible for the GRB prompt emission is (are) not identified. These models are critically reviewed and confronted with the current data.
Cite
Citations (0)
The rapid follow‐up of gamma‐ray burst (GRB) afterglows made possible by the multi‐wavelength satellite Swift, launched in November 2004, has put under a microscope the GRB early post‐burst behavior, This is leading to a significant reappraisal and expansion of the standard view of the GRB early afterglow behavior, and its connection to the prompt gamma‐ray emission. In addition to opening up the previously poorly known behavior on minutes to hours timescales, two other new pieces in the GRB puzzle being filled in are the the discovery and follow‐up of short GRB afterglows, and the opening up of the z ≳ 6 redshift range. We review some of the current theoretical interpretations of these new phenomena.
Swift
Cite
Citations (1)
We extend the standard fireball model, widely used to interpret gamma-ray burst (GRB) afterglow light curves, to include energy injections and apply the model to the afterglow light curves of GRB 990510, GRB 000301C, and GRB 010222. We show that discrete energy injections can cause temporal variations in the optical light curves, and we present fits to the light curves of GRB 000301C as an example. A continuous injection may be required to interpret other bursts, such as GRB 010222. The extended model accounts reasonably well for the observations in all bands ranging from X-rays to radio wavelengths. In some cases the radio light curves indicate that additional model ingredients may be needed.
Cite
Citations (30)
When does a GRB stop and its afterglow begin? A GRB may be defined as emission by internal shocks and its afterglow as emission by an external shock, but it is necessary to distinguish them observationally. With these definitions irregularly varying emission (at any frequency) must be the GRB, but smoothly varying intensity is usually afterglow. The GRB itself and its afterglow may overlap in time and in frequency, and distinguishing them will, in general, require detailed modeling.
Cite
Citations (1)
We present our multi‐band optical afterglow observations of the long duration GRB 021004 and GRB 030226 in combination with other published data to study the nature of the bursts. Optical afterglow light‐curves of both the GRBs exhibit signatures of collimated outflow. Observed superimposed variability in the case of GRB 021004, in the form of bumps and wiggles, suggest density fluctuations in the ambient medium. The derived temporal and spectral flux decay indices of GRB 030226 afterglow show an inconsistency with the theoretically predicted values.
Collimated light
Outflow
Cite
Citations (0)
Gamma-ray bursts (GRBs), which are bright flashes of gamma rays from extragalactic sources followed by fading afterglow emission, are associated with stellar core collapse events. We report the detection of very-high-energy (VHE) gamma rays from the afterglow of GRB 190829A, between 4 and 56 hours after the trigger, using the High Energy Stereoscopic System (H.E.S.S.). The low luminosity and redshift of GRB 190829A reduce both internal and external absorption, allowing determination of its intrinsic energy spectrum. Between energies of 0.18 and 3.3 tera-electron volts, this spectrum is described by a power law with photon index of 2.07 $\pm$ 0.09, similar to the x-ray spectrum. The x-ray and VHE gamma-ray light curves also show similar decay profiles. These similar characteristics in the x-ray and gamma-ray bands challenge GRB afterglow emission scenarios.
Spectral index
Cite
Citations (135)