Related papers: Can all breaks in GRB afterglows be explained by j…
Recent detections of GeV photons in a few GRBs by Fermi-LAT have led to strong constraints on the bulk Lorentz factor in GRB outflows. To avoid a large gamma-gamma optical depth, minimum values of the Lorentz factor have been estimated to…
A two-component jet model is proposed to explain the unusual afterglow of GRB 070419A. Regarding the optical light curve, a wide "jet" with an opening angle of > 30-40 degrees is assumed to produce the late shallow decay, while the three…
GRB 100418A is a long burst at z=0.624 without detection of any associated supernova (SN). Its lightcurves in both the prompt and afterglow phases are similar to GRB 060614, a nearby long GRB without an associated SN. We analyze the…
Late X-ray flares observed in X-ray afterglows of gamma-ray bursts (GRBs) suggest late central engine activities at a few minuets to hours after the burst. A few unambiguously confirmed cases of supernova associations with nearby long GRBs…
In several GRBs afterglows, rapid temporal decay is observed which is inconsistent with spherical (isotropic) blast-wave models. In particular, GRB 980519 had the most rapidly fading of the well-documented GRB afterglows, with t^{-2.05\pm…
Temporal behaviour of GRB afterglow light curve is derived for the case where the electron energy distribution is relatively flat, with the power-law index p lying between 1.0 and 2.0. It is shown that the expected behaviour will be the…
We use a sample of 19 Gamma Ray Bursts (GRBs) that exhibit single-peaked optical light curves to test the standard fireball model by investigating the relationship between the time of the onset of the afterglow and the temporal rising…
Long gamma-ray bursts (GRBs), which signify the end-life collapsing of very massive stars, are produced by extremely relativistic jets colliding into circumstellar medium. Huge energy is released both in the first few seconds, namely the…
The discovery of GRB 170817A, the first unambiguous off-axis short gamma-ray burst arising from a neutron star merger, has challenged our understanding of the angular structure of relativistic jets. Studies of the jet propagation usually…
Optical and radio afterglows arising from the shocks by relativistic conical ejecta running into pre-burst massive stellar winds are revisited. Under the homogeneous thin-shell approximation and a realistic treatment for the lateral…
The best-sampled afterglow light curves are available for GRB 030329. A distinguishing feature of this event is the obvious rebrightening at around 1.6 days after the burst. Proposed explanations for the rebrightening mainly include the…
Gamma-ray bursts (GRBs) are emitted by relativistic ejecta from powerful cosmic explosions. Their light curves suggest that the gamma-ray emission occurs at early stages of the ejecta expansion, well before it decelerates in the ambient…
We show that simple kinematic arguments can give limits on the timescale and amplitude of variabilities in gamma-ray burst (GRB) afterglows, especially when the variability timescale is shorter than the observed time since the burst \Delta…
Gamma-ray bursts (GRBs) associated with gravitational wave events are, and will likely continue to be, viewed at a larger inclination than GRBs without gravitational wave detections. As demonstrated by the afterglow of GW170817, this…
We demonstrate that gamma-ray burst afterglow spectra and light curves can be calculated for arbitrary explosion and radiation parameters by scaling the peak flux and the critical frequencies connecting different spectral regimes. Only one…
We describe our attempt to determine if gamma-ray burst (GRB) and afterglow emissions could both arise in external shocks for simple GRBs--bursts consisting of just a few peaks in their lightcurves. We calculate peak flux and peak frequency…
Evidence suggests that the gamma-ray burst (GRB) ejecta is likely magnetized, although the degree of magnetization of the ejecta is unknown. We derive a rigorous analytical solution for the relativistic 90 degree shocks under the ideal MHD…
We present broad-band observations of the afterglow and environment of the short GRB 111020A. An extensive X-ray light curve from Swift/XRT, XMM-Newton and Chandra, spanning ~100 seconds to 10 days after the burst, reveals a significant…
I discuss some theoretical expectations for the synchrotron emission from a relativistic blast-wave interacting with the ambient medium, as a model for GRB afterglows, and compare them with observations. An afterglow flux evolving as a…
The deaths of massive stars are sometimes accompanied by the launch of highly relativistic and collimated jets. If the jet is pointed towards Earth, we observe a "prompt" gamma-ray burst due to internal shocks or magnetic reconnection…