Open AccessDust and gas in the local environments of gamma‐ray bursts
Author(s) -
Schady P.,
Mason K. O.,
Page M. J.,
De Pasquale M.,
Morris D. C.,
Romano P.,
Roming P. W. A.,
Immler S.,
Vanden Berk D. E.
Publication year - 2007
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2007.11592.x
Subject(s) - physics , afterglow , astrophysics , gamma ray burst , extinction (optical mineralogy) , galaxy , astronomy , small magellanic cloud , large magellanic cloud , light curve , optics
Using a sample of gamma‐ray burst (GRB) afterglows detected by both the X‐Ray Telescope (XRT) and the UV/Optical Telescope (UVOT) on Swift , we modelled the spectral energy distributions (SEDs) to determine gas column densities and dust extinction in the GRB local environment. In six out of seven cases we find an X‐ray absorber associated with the GRB host galaxy with column density (assuming solar abundances) ranging from (0.8–7.7) × 10 21 cm −2 . We determine the rest‐frame visual extinction A V using the Small Magellanic Cloud (SMC), Large Magellanic Cloud (LMC) and Galactic extinction curves to model the dust in the GRB host galaxy, and this ranges from A V = 0.12 ± 0.04 to 0.65 +0.08 −0.07 . The afterglow SEDs were typically best fit by a model with an SMC extinction curve. In only one case was the GRB afterglow better modelled by a Galactic extinction curve, which has a prominent absorption feature at 2175 Å. We investigate the selection effects present in our sample and how these might distort the true distribution of A V in GRB host galaxies. We estimate that GRBs with no afterglow detected blueward of 5500 Å have average rest‐frame visual extinctions almost eight times those observed in the optically bright population of GRBs. This may help account for the ∼1/3 of GRBs observed by Swift that have no afterglow detected by UVOT.