Related papers: GRB Light Curves in the Relativistic Turbulence Mo…
Recent detections of GeV photons in a few GRBs by Fermi-LAT imply huge bulk Lorentz factors to avoid a large gamma gamma optical depth at high energy. Estimates can be as high as Gamma ~ 1000 in the most extreme cases. This puts severe…
The most luminous GRBs can be explained in terms of models involving stellar mass central engines only if the ejecta are beamed. As was pointed out by Rhoads, the dynamics of the blast wave, formed by the beamed ejecta sweeping the external…
We review the observational differences between gamma-ray bursts occurring on a single shell (such as in the external shock model) and multiple shells (such as in the internal shock model). We do not argue against external shocks or for…
Long duration gamma-ray bursts (GRBs) are among the least understood astrophysical transients powering the high-energy universe. To date, various mechanisms have been proposed to explain the observed electromagnetic GRB emission. In this…
We consider a model in which the ultra-relativistic jet in a gamma-ray burst (GRB) is cold and magnetically accelerated. We assume that the energy flux in the outflowing material is partially thermalized via internal shocks or a reverse…
Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks e.g. gamma-ray bursts (GRBs) active galactic nuclei (AGNs) and microquasars commonly exhibit power-law emission spectra. Recent PIC simulations…
Multi-wavelength light curves of bright gamma-ray blazars (e.g., 3C 454.3) reveal strong correlations across wavebands, yet striking dissimilarities in the details. This conundrum can be explained if the variable flux and polarization…
We propose that the internal energy of the GRB blast waves, thought to be stored in the form of relativistic protons co-moving with the blast wave, is converted explosively (i.e. on light crossing time scales) into relativistic electrons of…
The prompt GRB emission is thought to arise from electrons accelerated in internal shocks propagating within a highly relativistic outflow. The launch of Fermi offers the prospect of observations with unprecedented sensitivity in…
Cosmological $\gamma$-ray bursts originate from relativistic winds. Temporal fluctuations in the wind velocity can give rise to internal shocks which dissipate a significant fraction of the wind kinetic energy. Part of the energy dissipated…
Gamma-ray bursts are believed to be some catastrophic event in which material is ejected at a relativistic velocity, and internal collisions within this ejecta produce the observed $\gamma$-ray flash. The angular size of a causally…
In a recent paper we have calculated the power density spectrum of Gamma-Ray Bursts arising from multiple shocks in a relativistic wind. The wind optical thickness is one of the factors to which the power spectrum is most sensitive,…
After many years of speculation, recent observations have confirmed the association of gamma-ray bursts with core-collapse supernova explosions from massive stars. This association carries with it important consequences. The burst…
We performed accurate numerical calculations of angle-, time-, and frequency-dependent radiative transfer for the relativistic motion of matter in gamma-ray burst (GRB) models. Our technique for solving the transfer equation, which is based…
We present the results of our study of the variability time scales of a sample of 27 long Swift Gamma-Ray Bursts (GRBs) with known redshifts. The variability time scale can help our understanding of fundamental GRB parameters such as the…
Several patterns have been discovered in how some spectral characteristics change during the decaying phase of long (> few s.) GRB pulses. We compare these observed signatures with those expected from a relativistically expanding shell.…
According to the fireball model GRBs are produced when a relativistic flow is dissipated by shocks. The questions how does a GRB's "inner engine" accelerates and collimated the relativistic flow is today the most interesting (and most…
We explore several models which might be proposed to explain recent possible detections of high-energy (TeV) gamma rays in association with low-energy gamma-ray bursts (GRBs). Likely values (and/or upper limits) for the source energies in…
Lorentz invariance violations (LIV) can yield vacuum birefringence, which results in an energy-dependent rotation of the polarization vector of linearly polarized emission from astrophysical sources. It is believed that if the relative…
A perturbing shell is introduced as a device for studying the excitation of fluid motions in relativistic stellar models. We show that this approach allows a reasonably clean separation of radiation from the shell and from fluid motions in…