In the external shock model, gamma-ray burst (GRB) emissions are produced by the energization and deceleration of a thin relativistic blast wave due to its interactions with the circumburst medium (CBM). We study the physical properties of an analytic function which describes temporally-evolving GRB spectra in the limit of a smooth CBM with density n(x) ∝ x−η, where x is the radial coordinate. ...

An important concern in the application of gamma-ray bursts (GRBs) to cosmology is that the calibration of GRB luminosity/energy relations depends on the cosmological model, due to the lack of a sufficient lowredshift GRB sample. In this paper, we present a new method to calibrate GRB relations in a cosmologyindependent way. Since objects at the same redshift should have the same luminosity dis...

We present millimetre (mm) and submillimetre (submm) photometry of a sample of five host galaxies of Gamma Ray Bursts (GRBs), obtained using the MAMBO2 and SCUBA bolometer arrays respectively. These observations were obtained as part of an ongoing project to investigate the status of GRBs as indicators of star formation. Our targets include two of the most unusual GRB host galaxies, selected as...

We calculate the time evolution of the flux, apparent size, and image centroid motion of gamma-ray burst (GRB) jets in the radio, and show that they can be resolved by the VLBA at distances of hundreds of Mpc. We find that GRB 030329 which showed spectroscopic evidence for an associated supernova (SN) Type Ib/c at a distance of ≈ 800 Mpc might just be resolvable by VLBA after several months. Th...

This paper reports on the results of a numerical investigation designed to address how the initially anisotropic appearance of a GRB remnant is modified by the character of the circumburst medium and by the possible presence of an accompanying supernova (SN). Axisymmetric hydrodynamical calculations of light, impulsive jets propagating in both uniform and inhomogeneous external media are presen...

We report on the BeppoSAX data analysis of the afterglow of Gamma–Ray Burst (GRB) 990123, one of the brightest GRBs detected by BeppoSAX. Mainly due to its exceptional brightness, this is the only source for which the Wide Field Cameras have allowed an early detection of the X–ray afterglow between ∼20 and 60 min after the GRB trigger. Besides, again for the first time, high-energy emission fro...

We present optical and near-IR observations of the host galaxy of GRB 020127, for which we measure R Ks 1⁄4 6:2mag. This is only the second GRB host to date classified as an ERO. The spectral energy distribution (SED) is typical of a dusty starburst galaxy, with a redshift z 1:9, a luminosity L 5L , and an inferred stellar mass of M 10 10 M , two orders of magnitude moremassive than typical GRB...

We study the incidence rate of damped Lyα systems associated with the host galaxies of gamma-ray bursts (GRB-HOST-DLAs) as functions of neutral hydrogen column density (NHI) and projected star formation rate (SFR) using cosmological SPH simulations. Assuming that the occurrence of GRBs is correlated with the local SFR, we find that the median NHI of GRB-HOST-DLAs progressively shifts to lower N...

There has been increasing evidence that at least some GRBs are emission beamed. The beamed GRB afterglow evolution has been discussed by several authors in the ultra-relativistic case. It has been shown that the dynamics of the blast wave will be significantly modified by the sideways expansion, and there may be a sharp break in the afterglow light curves under certain circumstances. However, t...