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X-ray absorption of $gamma$-ray burst (GRB) afterglows is prevalent yet poorly understood. X-ray derived neutral hydrogen column densities ($N_{rm H}$) of GRB X-ray afterglows show an increase with redshift, which might give a clue for the origin of this absorption. We use more than 350 X-ray afterglows with spectroscopic redshift ($z$) from the Swift XRT repository as well as over 100 Ly,$alpha$ absorption measurements in $z>1.6$ sources. The observed trend of the average optical depth $tau$ at 0.5 keV is consistent with both a sharp increase of host $N_{rm H}(z)$, and an absorbing diffuse intergalactic medium, along with decreasing host contribution to $tau$. We analyze a sub-sample of high-$z$ GRBs with $N_{rm H}$ derived both from the X-ray afterglow and the Ly,$alpha$ line. The increase of X-ray derived $N_{rm H}(z)$ is contrasted by no such increase in the Ly,$alpha$ derived column density. We argue that this discrepancy implies a lack of association between the X-ray and Ly,$alpha$ absorbers at high-$z$. This points towards the X-ray absorption at high $z$ being dominated by an intervening absorber, which lends credibility to an absorbing intergalactic medium contribution.
Spectropolarimetric measurements of gamma-ray burst (GRB) optical afterglows contain polarization information for both continuum and absorption lines. Based on the Zeeman effect, an absorption line in a strong magnetic field is polarized and split in
We derive basic analytical results for the timing and decay of the GRB-counterpart and delayed-afterglow light-curves for a brief emission episode from a relativistic surface endowed with angular structure, consisting of a uniform Core of size theta_
The afterglow emission from gamma-ray bursts (GRBs) is believed to originate from a relativistic blast wave driven into the circumburst medium. Although the afterglow emission from radio up to X-ray frequencies is thought to originate from synchrotro
We study thermal emission from circumstellar structures heated by gamma-ray burst (GRB) radiation and ejecta and calculate its contribution to GRB optical and X-ray afterglows using the modified radiation hydro-code small STELLA. It is shown that the
For gamma-ray bursts (GRBs) with a plateau phase in the X-ray afterglow, a so called $L-T-E$ correlation has been found which tightly connects the isotropic energy of the prompt GRB ($E_{gamma,rm{iso}}$) with the end time of the X-ray plateau ($T_{a}