Related papers: Optical and gamma-ray emissions from internal forw…
Fermi satellite discovered that cosmological gamma-ray bursts (GRBs) are accompanied by long GeV flashes. In two GRBs, an optical counterpart of the GeV flash has been detected. Recent work suggests that the GeV+optical flash is emitted by…
Collisionless entrainment of the surrounding matter imports the relativistic baryon component in the Gamma-Ray Burst (GRB) fireball frame. We show that half the fireball energy can be transferred from radiation to the comoving hot motions…
We show that the light curve of the double GeV+optical flash in GRB 130427A is consistent with radiation from the blast wave in a wind-type medium with density parameter $A=\rho r^2\sim 5\times 10^{10}$ g cm$^{-1}$. The peak of the flash is…
GRB030329 displays one clear and, possibly, multiple less intense fast-rising ($\Delta t / t \sim 0.3$) jumps in its optical afterglow light curve. The decay rate of the optical light curve remains the same before and after the photon flux…
Two main types of models have been suggested to explain the long durations and multiple peaks of Gamma-Ray Bursts (GRBs). In one, there is a very quick release of energy at a central site resulting in a single relativistic shell that…
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 GRB afterglows, this formalism is more suitable if the relativistic…
The internal shock model for gamma-ray bursts involves shocks taking place in a relativistic wind with a very inhomogeneous initial distribution of the Lorentz factor. We have developed a 1D lagrangian hydrocode to follow the evolution of…
Gamma-ray bursts (GRBs) are luminous stellar explosions characterized by the ejection of relativistic jets. This work proposes a novel paradigm to study these GRB jets. By analyzing the timing information of prompt pulses and X-ray flares,…
Long-duration gamma-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterised by an initial phase of bright and highly variable radiation in the keV-MeV band…
An analysis of the interaction between a spherical relativistic blast-wave shell and a stationary cloud with a spherical cap geometry is performed assuming that the cloud width << x, where x is the distance of the cloud from the GRB…
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…
Despite being hard to measure, GRB prompt $\gamma$-ray emission polarization is a valuable probe of the dominant emission mechanism and the outflow's composition and angular structure. During the prompt emission the outflow is…
We calculate the reverse shock (RS) synchrotron emission in the optical and the radio wavelength bands from electron-positron pair enriched gamma-ray burst ejecta with the goal of determining the pair content of GRBs using early time…
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 are estimated to be as…
We discuss the origin of X-Ray Flashes (XRFs), a recently discovered class of Gamma-Ray Bursts (GRBs). Using a simplified model for internal shocks we check if XRFs can be intrinsically soft due to some specific values of the parameters…
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…
Very early optical and near infrared (IR) emission was discovered accompanying the long gamma-ray burst (GRB) 041219a. We show that the optical/IR flash tracking the gamma-ray lightcurve during the prompt emission could be understood as…
Several trends have been identified in the prompt gamma-ray burst (GRB) emission: e.g. hard-to-soft evolution, pulse width evolution with energy, time lags, hardness-intensity/-fluence correlations. Recently Fermi has significantly extended…
We show that, contrary to common belief, internal shocks can arise in an accelerating radiation-dominated jet if it is confined even weakly to a converging opening angle because the acceleration declines. The radiation-dominated internal…
Gonz\'alez et al. (2003) have reported the discovery of an anomalous radiation component from ~ 1 -- 200 MeV in GRB 941017. This component varies independently of and contains >~ 3 times the energy found in the prompt ~ 50 keV -- 1 MeV…