Related papers: Polarization and light curve variability: the "pat…
Polarization has been observed in a number of GRB afterglows. We briefly review the models that have been proposed to account for the observed polarization levels. We summarize the observations and the attempts to explain them with existing…
Randomly oriented relativistic emitters in a relativistically expanding shell provides an alternative to internal shocks as a mechanism for producing GRBs' variable light curves with efficient conversion of energy to radiation. In this…
We have performed detailed calculations of spectra and light curves of GRB afterglows assuming that the observed GRBs can have a jet geometry. The calculations are based on an expanding relativistic shock GRB afterglow model where the…
Gamma-ray bursts (GRBs) are powered by ultra-relativistic jets. The launching sites of these jets are surrounded by dense media, which the jets must cross before they can accelerate and release the high energy emission. Interaction with the…
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…
Among the large variety of astrophysical sources that we can observe, gamma-ray bursts (GRBs) are the most energetic of the whole Universe. The definition of a general picture describing the physics behind GRBs has always been a compelling…
GRB afterglow polarization is discussed. We find an observable, up to 10%, polarization, if the magnetic field coherence length grows at about the speed of light after the field is generated at the shock front. Detection of a polarized…
Polarization measurements for the optical counterpart to GRB 021004 are presented and discussed. Our observations were performed with the TNG and the VLT-UT3 (Melipal) during the first and fourth night after the gamma-ray burst discovery.…
We report the detection of significant polarization in the optical afterglow of GRB990712 on three instances 0.44, 0.70 and 1.45 days after the gamma-ray burst, with (P, theta) being (2.9% +- 0.4%, 121.1 degr +- 3.5 degr), (1.2% +- 0.4%,…
Polarization measurements for the optical counterpart to GRB 020405 are presented and discussed. Our observations were performed with the VLT-UT3 (Melipal) during the second and third night after the gamma-ray burst discovery. The…
The Swift era has posed a challenge to the standard blast-wave model of Gamma Ray Burst (GRB) afterglows. The key observational features expected within the model are rarely observed, such as the achromatic steepening (`jet-break') of the…
We derive light curves of the afterglow emission from highly collimated jets if the power-law index ($p$) of the electron energy distribution is above 1 but below 2. We find (1) below the characteristic synchrotron frequency, the light…
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 review some open problems in the physics of afterglows, namely their polarization properties and the existence of dark/faint bursts. Polarization studies yield precious insights in the physical structure and dynamical evolution of GRB…
Long gamma ray bursts (GRBs) are produced by the collapse of some very massive stars, which emit ultra-relativistic jets. When the jets collide with the interstellar medium they decelerate and generate the so-called afterglow emission,…
Gamma-Ray Burst (GRB) afterglows are commonly interpreted as synchrotron emission from a relativistic blast wave produced by a point explosion in an ambient medium, plausibly the interstellar medium of galaxies. We calculate the amplitude…
The polarization curve of GRB 020813 is discussed and compared to different models for the structure, evolution and magnetisation properties of the jet and the interstellar medium onto which the fireball impacts. GRB 020813 is best suited…
Jet precessions are widely involved in astrophysical phenomena from galaxies to X-ray binaries and gamma-ray bursts (GRBs). Polarization presents a unique probe of the magnetic fields in GRB jets. The precession of GRBs relativistic jets…
We consider some recent developments in GRB/afterglow observations: (i) the appearance of a very hard prompt component in GRB 941017, and (ii) variability in the early afterglow light curves of GRB 021004 and GRB 030329. We show that these…
We investigate the effect that the structure of GRB jets has on the afterglow light curves for observers located at different viewing angles, $\theta_{obs}$, from the jet symmetry axis. The largest uncertainty in the jet dynamics is the…