Highly-ionized metals as probes of the circumburst gas in the natal regions of gamma-ray bursts

DOI: 
10.1093/mnras/sty1447
Publication date: 
01/06/2018
Main author: 
Heintz, K. E.
IAA authors: 
Cano, Z.;Thöne, C. C.;de Ugarte Postigo, A.
Authors: 
Heintz, K. E.;Watson, D.;Jakobsson, P.;Fynbo, J. P. U.;Bolmer, J.;Arabsalmani, M.;Cano, Z.;Covino, S.;D'Elia, V.;Gomboc, A.;Japelj, J.;Kaper, L.;Krogager, J. -K.;Pugliese, G.;Sánchez-Ramírez, R.;Selsing, J.;Sparre, M.;Tanvir, N. R.;Thöne, C. C.;de Ugarte Postigo, A.;Vergani, S. D.
Journal: 
Monthly Notices of the Royal Astronomical Society
Refereed: 
Yes
Publication type: 
Article
Pages: 
3456-3476
Abstract: 
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 N V λλ 1238,1242 line transitions, but we also discuss other high-ionization lines such as O VI, C IV and Si IV. We find no correlation between the column density of N V and the neutral gas properties such as metallicity, H I column density and dust depletion, however the relative velocity of N V, typically a blueshift with respect to the neutral gas, is found to be correlated with the column density of H I. This may be explained if the N V gas is part of an H II 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 2σ significance) that the X-ray derived column density, N<SUB>H, X</SUB>, may be correlated with the column density of N V, 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 N V (and also O VI) 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.
Database: 
ADS
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2018MNRAS.479.3456H/abstract
ADS Bibcode: 
2018MNRAS.479.3456H
Keywords: 
gamma-ray bursts: general;ISM: abundances;Astrophysics - High Energy Astrophysical Phenomena;Astrophysics - Astrophysics of Galaxies