ﻻ يوجد ملخص باللغة العربية
The dust extinction of gamma-ray bursts (GRBs) host galaxies, containing important clues to the nature of GRB progenitors and crucial for dereddening, is still poorly known. Here we propose a straightforward method to determine the extinction of GRB host galaxies by comparing the observed optical spectra to the intrinsic ones extrapolated from the X-ray spectra. The rationale for this method is from the standard fireball model: if the optical flux decay index equals to that of the X-ray flux, then there is no break frequency between the optical and X-ray bands, therefore we can derive the intrinsic optical flux from the X-ray spectra. We apply this method to three GRBs of which the optical and X-ray fluxes have the same decay indices and another one with inferred cooling break frequency, and obtain the rest-frame extinction curves of their host galaxies. The derived extinction curves are gray and do not resemble any extinction curves of local galaxies (e.g. the Milk Way, the Small/Large Magellanic Clouds, or nearby starburst galaxies). The amount of extinction is rather large (with visual extinction $A_V$ $sim$ 1.6--3.4$magni$). We model the derived extinction curves in terms of the silicate-graphite interstellar grain model. As expected from the ``gray nature of the derived extinction curve, the dust size distribution is skewed to large grains. We determine, for the first time, the local dust-to-gas ratios of GRB host galaxies using the model-derived dust parameters and the hydrogen column densities determined from X-ray absorptions.
The composition and amount of interstellar dust within gamma-ray burst (GRB) host galaxies is of key importance when addressing selection effects in the GRB redshift distribution, and when studying the properties of their host galaxies. As well as th
In order to study the effect of dust extinction on the afterglow of gamma-ray bursts (GRBs), we carry out numerical calculations with high precision based on rigorous Mie theory and latest optical properties of interstellar dust grains, and analyze t
We put stringent constraints for the first time on the dust properties in the circumburst medium of a gamma-ray burst (GRB) afterglow. This is based on the optical spectrum of GRB 020813 (z=1.255), obtained with Keck I LRIS 4.65 h after the burst. Fr
In this paper we present the results from the analysis of a sample of 28 gamma-ray burst (GRB) afterglow spectral energy distributions, spanning the X-ray through to near-infrared wavelengths. This is the largest sample of GRB afterglow spectral ener
We report on the results of a study to obtain limits on the absorbing columns to wards an initial sample of 10 long Gamma-Ray Bursts observed with BeppoSAX, using a new approach to SED fitting to nIR, optical and X-ray afterglow data, in count space