Related papers: On the existence of a reverse shock in magnetized …
A number of gamma-ray bursts (GRBs) exhibit the late simultaneous bumps in their optical and Xray afterglows around the jet break. Its origin is unclear. Based on the following two facts, we suggest that this feature may sound a transition…
The X-ray light curves of the early afterglow phase from gamma-ray bursts present a puzzling variability, including flares. The origin of these flares is still debated, and often associated with a late activity of the central engine. We…
Gamma Ray Bursts (GRBs) are characterized by ultra-relativistic outflows, while supernovae are generally characterized by non-relativistic ejecta. GRB afterglows decelerate rapidly usually within days, because their low-mass ejecta rapidly…
The afterglow of gamma-ray bursts (GRBs) has been extensively discussed in the context of shocks generated during an interaction of relativistic outflows with their ambient medium. This process leads to the formation of both a forward and a…
Whether gamma-ray bursts are highly beamed or not is a very difficult but important problem that we are confronted with. Some theorists suggest that beaming effect usually leads to a sharp break in the afterglow light curve during the…
The peak time of optical afterglow may be used as a proxy to constrain the Lorentz factor Gamma of the gamma-ray burst (GRB) ejecta. We revisit this method by including bursts with optical observations that started when the afterglow flux…
Gamma-ray burst afterglows arise from relativistic collisionless shocks in which the postshock tangled magnetic field $\vec{B}$ is produced by the two-stream and/or Weibel instabilities on plasma skin-depth scales $(c/\omega_p)$. The field…
Short gamma-ray bursts (GRBs) are the aftermath of compact binary mergers involving neutron stars. If the merger remnant is a millisecond magnetar instead of a black hole, a significant proportion of the rotational energy deposited to the…
We present observations of the possible short GRB 180418A in $\gamma$-rays, X-rays, and in the optical. Early optical photometry with the TAROT and RATIR instruments show a bright peak ($\approx$ 14.2 AB mag) between $T+28$ and $T+90$…
Millisecond magnetars, one of the potential candidates for the central engine of Gamma-ray bursts (GRBs), can experience significant magnetic field enhancement shortly after their formation. In some cases, this evolution is further…
Approximately 1/4-1/2 of short duration Gamma-Ray Bursts are followed by variable X-ray emission lasting ~ 100 s with a fluence comparable or exceeding that of the initial burst itself. The long duration and significant energy of this…
As it was recently shown by Derishev etal (1999), initial GRB ejecta are likely to contain comparable number of protons and neutrons. During acceleration process, and/or later, due to interaction with external medium, such ejecta are likely…
The shock system that produces the afterglow to GRBs consists of a forward- and a reverse-shock. For short GRBs, observational evidence for a reverse-shock has been sparse, however, the afterglow to GRB 160821B requires a reverse-shock at…
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…
A long-duration gamma-ray burst (GRB) has been widely thought to arise from the collapse of a massive star, and it has been suggested that its ambient medium is a homogenous interstellar medium (ISM) or a stellar wind. There are two shocks…
Observations by the {\RHESSI} satellite of large polarization of the prompt $\gamma$-ray emission from the Gamma Ray Burst GRB021206 \citep{coburn03} imply that the magnetic field coherence scale is larger than the size of the visible…
Variability on time scales \delta t < t is observed in many gamma-ray burst afterglows. It is well known that there should be no such variability if the afterglow is emitted by external shock, which is produced by the interaction of…
We discuss the implications of Fermi/LAT observations on several aspects of gamma-ray burst (GRB) physics, including the radiation process, the emission sites, the bulk Lorentz factor, and the pre-shock magnetic field: (1) MeV-range…
Abridged.-- We demonstrate that the radiation emitted by ultrarelativistic electrons in highly nonuniform, small-scale magnetic fields is different from synchrotron radiation if the electron's transverse deflections in these fields are much…
Using GRB radio afterglow observations, we calculate the fraction of shocked plasma energy in the magnetic field in relativistic collisionless shocks ($\epsilon_B$). We obtained $\epsilon_B$ for 38 bursts by assuming that the radio…