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We present here a survey of high-ionization absorption lines in the afterglow spectra of longduration 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 Nλλ 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 N and the neutral gas properties such as metallicity, H column density, and dust depletion; however, the relative velocity of N, typically a blueshift with respect to the neutral gas, is found to be correlated with the column density of H. This may be explained if the N gas is part of an H 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, may be correlated with the column density of N, 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 (and also O) 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.© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. ; We would like to thank the referee for a clear and thorough report, which greatly improved the presentation of the results in the paper. We also wish to thank K. Wiersema and P. Moller for enlightening discussions. KEH and PJ acknowledge support by a Project Grant (162948-051) from The Icelandic Research Fund. JK acknowledges financial support from the Danish Council for Independent Research (EU-FP7 under the Marie-Curie grant agreement no. 600207) with reference DFF-MOBILEX-5051-00115. JJ acknowledges support from NOVA and NWO-FAPESP grant for advanced instrumentation in astronomy. AG acknowledges the financial support from the Slovenian Research Agency (research core funding no. P1-0031 and project grant no. J1-8136). AdUP, CCT, and ZC acknowledge support from the Spanish Ministry of Economy and Competitivity under grant number AYA 2014-58381-P. AdUP and CCT acknowledge support from Ramon y Cajal fellowships (RyC-2012-09975 and RyC-2012-09984). AdUP acknowledges support from a grant from the BBVA foundation for researchers and cultural creators. ZC acknowledges support from the Juan de la Cierva Incorporacion fellowship IJCI-2014-21669 and from the Spanish research project AYA 2014-58381-P. RS-R acknowledges support from ASI (Italian Space Agency) through the contract no. 2015-046-R.0 and from European Union Horizon 2020 Programme under the AHEAD project (grant agreement no. 654215).

Publisher's version (útgefin grein) ; 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 Vλλ 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, NH, X, 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. ; KEH and PJ acknowledge support by a Project Grant (162948–051) from The Icelandic Research Fund. JK acknowledges financial support from the Danish Council for Independent Research (EU-FP7 under the Marie-Curie grant agreement no. 600207) with reference DFF–MOBILEX–5051–00115. JJ acknowledges support from NOVA and NWO-FAPESP grant for advanced instrumentation in astronomy. AG acknowledges the financial support from the Slovenian Research Agency (research core funding no. P1-0031 and project grant no. J1-8136). AdUP, CCT, and ZC acknowledge support from the Spanish Ministry of Economy and Competitivity under grant number AYA 2014-58381-P. AdUP and CCT acknowledge support from Ramon y Cajal fellowships (RyC-2012-09975 and RyC-2012-09984). AdUP acknowledges support from a grant from the BBVA foundation for researchers and cultural creators. ZC acknowledges support from the Juan de la Cierva Incorporación fellowship IJCI-2014-21669 and from the Spanish research project AYA 2014-58381-P. RS-R acknowledges support from ASI (Italian Space Agency) through the contract no. 2015-046-R.0 and from European Union Horizon 2020 Programme under the AHEAD project (grant agreement no. 654215). ; Peer Reviewed

It is notoriously difficult to localize short γ-ray bursts (sGRBs) and their hosts to measure their redshifts. These measurements, however, are critical for constraining the nature of sGRB progenitors, their redshift distribution, and the r-process element enrichment history of the universe. Here we present spectroscopy of the host galaxy of GRB 111117A and measure its redshift to be z = 2.211. This makes GRB 111117A the most distant high-confidence short duration GRB detected to date. Our spectroscopic redshift supersedes a lower, previously estimated photometric redshift value for this burst. We use the spectroscopic redshift, as well as new imaging data to constrain the nature of the host galaxy and the physical parameters of the GRB. The rest-frame X-ray derived hydrogen column density, for example, is the highest compared to a complete sample of sGRBs and seems to follow the evolution with redshift as traced by the hosts of long GRBs. From the detection of Lyα emission in the spectrum, we are able to constrain the escape fraction of Lyα in the host. The host lies in the brighter end of the expected sGRB host brightness distribution at z = 2.211, and is actively forming stars. Using the observed sGRB host luminosity distribution, we find that between 43% and 71% of all Swift-detected sGRBs have hosts that are too faint at z ∼ 2 to allow for a secure redshift determination. This implies that the measured sGRB redshift distribution could be incomplete at high redshift. The high z of GRB 111117A is evidence against a lognormal delay-time model for sGRBs through the predicted redshift distribution of sGRBs, which is very sensitive to high-z sGRBs. From the age of the universe at the time of GRB explosion, an initial neutron star (NS) separation of a < 3.1 R is required in the case where the progenitor system is a circular pair of inspiralling NSs. This constraint excludes some of the longest sGRB formation channels for this burst.© 2018 ESO. ; We thank the anonymous referee for the constructive report. We thank Jens Hjorth and Lise Christensen for useful discussions regarding the interpretation of this event. We thank Mathieu Puech for testing the possible contribution from an older stellar population in the SED. We thank Peter Laursen for fruitful discussions regarding the Ly alpha escape fraction. TK acknowledges support through the Sofja Kovalevskaja Award to P. Schady. SDV is supported by the French National Research Agency (ANR) under contract ANR-16-CE31-0003 BEaPro. PDA and SCo acknowledge support from ASI grant I/004/11/3. JJ acknowledges support from NOVA and a NWO-FAPESP grant for advanced instrumentation in astronomy. NRT and KW acknowledge support from STFC Consolidated Grant ST/N000757/1. CT acknowledges support from a Spanish National Research Grant of Excellence under project AYA 2014-58381-P and funding associated with a Ramon y Cajal fellowship under grant number RyC-2012-09984. AdUP acknowledges support from a Ramon y Cajal fellowship, a BBVA Foundation Grant for Researchers and Cultural Creators, and the Spanish Ministry of Economy and Competitiveness through project AYA2014-58381-P. ZC acknowledges support from the Spanish research project AYA 2014-58381-P and support from Juan de la Cierva Incorporacion fellowships IJCI-2014-21669. RSR acknowledges AdUP's BBVA Foundation Grant for Researchers and Cultural Creators and support from the Italian Space Agency (ASI) through Contract n. 2015-046-R.0 and from the European Union Horizon 2020 Programme under the AHEAD project (grant agreement n. 654215). This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013). The analysis and plotting was achieved using the Python-based packages Matplotlib (Hunter 2007), Numpy, and Scipy (van der Walt et al. 2011), along with other community-developed packages. This work made use of observations obtained with the Italian 3.6m Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundacion Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on data from the GTC Archive at CAB (INTA-CSIC) and on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina), and Ministerio da Ciencia, Tecnologia e Inovacao (Brazil).

In this work we present spectra of all γ-ray burst (GRB) afterglows that have been promptly observed with the X-shooter spectrograph until 31/03/2017. In total, we have obtained spectroscopic observations of 103 individual GRBs observed within 48 hours of the GRB trigger. Redshifts have been measured for 97 per cent of these, covering a redshift range from 0.059 to 7.84. Based on a set of observational selection criteria that minimise biases with regards to intrinsic properties of the GRBs, the follow-up effort has been focused on producing a homogeneously selected sample of 93 afterglow spectra for GRBs discovered by the Swift satellite. We here provide a public release of all the reduced spectra, including continuum estimates and telluric absorption corrections. For completeness, we also provide reductions for the 18 late-time observations of the underlying host galaxies. We provide an assessment of the degree of completeness with respect to the parent GRB population, in terms of the X-ray properties of the bursts in the sample and find that the sample presented here is representative of the full Swift sample. We have constrained the fraction of dark bursts to be <28 per cent and confirm previous results that higher optical darkness is correlated with increased X-ray absorption. For the 42 bursts for which it is possible, we have provided a measurement of the neutral hydrogen column density, increasing the total number of published HI column density measurements by ∼33 per cent. This dataset provides a unique resource to study the ISM across cosmic time, from the local progenitor surroundings to the intervening Universe.© ESO 2019. ; JPUF, BMJ and DX acknowledge support from the ERC-StG grant EGGS-278202. The Dark Cosmology Centre was funded by the Danish National Research Foundation. This work was supported by a VILLUM FONDEN Investigator grant to JH (project number 16599). TK acknowledges support by the European Commission under the Marie Curie Intra-European Fellowship Programme in FP7. LK and JJ acknowledges support from NOVA and NWO-FAPESP grant for advanced instrumentation in astronomy. KEH and PJ acknowledge support by a Project Grant (162948-051) from The Icelandic Research Fund. AG acknowledges the financial support from the Slovenian Research Agency (research core funding No. P1-0031 and project grant No. J1-8136). CT acknowledges support from a Spanish National Research Grant of Excellence under project AYA 2014-58381-P and funding associated to a Ramon y Cajal fellowship under grant number RyC-2012-09984. AdUP acknowledges support from a Ramon y Cajal fellowship, a BBVA Foundation Grant for Researchers and Cultural Creators, and the Spanish Ministry of Economy and Competitiveness through project AYA2014-58381-P. ZC acknowledges support from the Spanish research project AYA 2014-58381-P and support from Juan de la Cierva Incorporacion fellowships IJCI-2014-21669. DAK acknowledges support from the Spanish research project AYA 2014-58381-P and support from Juan de la Cierva Incorporacion fellowships IJCI-2015-26153. RSR acknowledges AdUP's BBVA Foundation Grant for Researchers and Cultural Creators and support from ASI (Italian Space Agency) through the Contract n. 2015-046-R.0 and from European Union Horizon 2020 Programme under the AHEAD project (grant agreement n. 654215). GL is supported by a research grant (19054) from VILLUM FONDEN. SDV acknowledges the support of the French National Research Agency (ANR) under contract ANR-16-CE31-0003 BEaPro DM acknowledges support from the Instrument Center for Danish Astrophysics (IDA). ; Peer Reviewed

Context. Long gamma-ray bursts (GRBs) are produced during the dramatic deaths of massive stars with very short lifetimes, meaning that they explode close to the birth place of their progenitors. Over a short period they become the most luminous objects observable in the Universe, being perfect beacons to study high-redshift star-forming regions. Aims. We aim to use the afterglow of GRB 161023A at a redshift z = 2.710 as a background source to study the environment of the explosion and the intervening systems along its line of sight. Methods. For the first time, we complement ultraviolet (UV), optical and near-infrared (NIR) spectroscopy with millimetre spectroscopy using the Atacama Large Millimeter Array (ALMA), which allows us to probe the molecular content of the host galaxy. The X-shooter spectrum shows a plethora of absorption features including fine-structure and metastable transitions of Fe, Ni, Si, C, and O. We present photometry ranging from 43 s to over 500 days after the burst. Results. We infer a host-galaxy metallicity of [Zn/H] = -1.11 ± 0.07, which, corrected for dust depletion, results in [X/H] = -0.94 ± 0.08. We do not detect molecular features in the ALMA data, but we derive limits on the molecular content of log(N/cm) < 15.7 and log(N/cm, which are consistent with those that we obtain from the optical spectra, log(N/cm)< 15.2 and log(N/cm) < 14.5. Within the host galaxy, we detect three velocity systems through UV, optical and NIR absorption spectroscopy, all with levels that were excited by the GRB afterglow. We determine the distance from these systems to the GRB to be in the range between 0.7 and 1.0 kpc. The sight line to GRB 161023A shows nine independent intervening systems, most of them with multiple components. Conclusions. Although no molecular absorption was detected for GRB 161023A, we show that GRB millimetre spectroscopy is now feasible and is opening a new window on the study of molecular gas within star-forming galaxies at all redshifts. The most favoured lines of sight for this purpose will be those with high metallicity and dust.© ESO 2018. ; AdUP and CT acknowledge support from Ramon y Cajal fellowships RyC-2012-09975 and RyC-2012-09984 and the Spanish Ministry of Economy and Competitiveness through projects AYA2014-58381-P and AYA2017-89384-P, AdUP furthermore from the BBVA foundation. DAK acknowledges support from the Spanish research project AYA 2014-58381-P, and from Juan de la Cierva Incorporacion fellowship IJCI-2015-26153. FEB acknowledges support from CONICYT-Chile (Basal-CATA PFB-06/2007) and the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. Part of the funding for GROND (both hardware as well as personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger (DFG grant HA 1850/28-1). JB acknowledges support through the Sofja Kovalevskaja Award to P. Schady from the Alexander von Humboldt Foundation of Germany. MJM acknowledges the support of the National Science Centre, Poland through the POLONEZ grant 2015/19/P/ST9/04010; this project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 665778. AG acknowledges the financial support from the Slovenian Research Agency (research core funding No. P1-0031 and project grant No. J1-8136) and networking support by the COST Action GWverse CA16104. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 098.A-0055, 098.D-0710 and 0100.D-0649. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.00862. T. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan) and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.