期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 479, 期 3, 页码 3456-3476出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/sty1447
关键词
gamma-ray bursts: general; ISM: abundances
资金
- Icelandic Research Fund [162948-051]
- Danish Council for Independent Research (EU-FP7 under the Marie-Curie grant) [600207, DFF-MOBILEX-5051-00115]
- NOVA
- NWO-FAPESP grant
- Slovenian Research Agency [P1-0031, J1-8136]
- Spanish Ministry of Economy and Competitivity [AYA 2014-58381-P]
- Ramon y Cajal fellowships [RyC-2012-09975, RyC-2012-09984]
- BBVA foundation for researchers and cultural creators
- Juan de la Cierva Incorporacion fellowship [IJCI-2014-21669]
- Spanish research project [AYA 2014-58381-P]
- ASI (Italian Space Agency) [2015-046-R.0]
- European Union Horizon 2020 Programme under the AHEAD project [654215]
We present here a survey of high-ionization absorption lines in the afterglow spectra of long-duration gamma-ray bursts (GRBs) obtained with the VLT/X-shooter spectrograph. Our main goal is to investigate the circumburst medium in the natal regions of GRBs. Our primary focus is on the NV lambda lambda 1238, 1242 line transitions, but we also discuss other high-ionization lines such as OVI, CIV, and SiIV. We find no correlation between the column density of NV and the neutral gas properties such as metallicity, HI column density, and dust depletion; however, the relative velocity of NV, typically a blueshift with respect to the neutral gas, is found to be correlated with the column density of HI. This may be explained if the NV gas is part of an HII region hosting the GRB, where the region's expansion is confined by dense, neutral gas in the GRB's host galaxy. We find tentative evidence (at 2 sigma significance) that the X-ray derived column density, N-H,N- X, may be correlated with the column density of NV, which would indicate that both measurements are sensitive to the column density of the gas located in the vicinity of the GRB. We investigate the scenario where NV (and also OVI) is produced by recombination after the corresponding atoms have been stripped entirely of their electrons by the initial prompt emission, in contrast to previous models where highly ionized gas is produced by photoionization from the GRB afterglow.
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