The high-redshift gamma-ray burst GRB 140515A. A comprehensive X-ray and optical study

Journal
Date Issued
2015
Author(s)
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Sánchez-Ramírez, R.
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Nappo, F.
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Japelj, J.
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de Ugarte Postigo, A.
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Oates, S.
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D'Elia, V.
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Gafton, E.
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Gnedin, N.
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Goldoni, P.
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Gorosabel, J.
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Libbrecht, T.
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Malesani, D.
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Thöne, C. C.
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Vergani, S. D.
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Xu, D.
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DOI
Description
We thank the anonymous referee for the valuable comments that contributed to improving the quality of the publication. This research has been supported by ASI grant INAF I/004/11/1. D.M. acknowledges support from the Instrument Center for Danish Astrophysics (IDA). The Dark Cosmology Centre is funded by the Danish National Research Foundation. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.
Abstract
High-redshift gamma-ray bursts (GRBs) offer several advantages when studying the distant Universe, providing unique information about the structure and properties of the galaxies in which they exploded. Spectroscopic identification with large ground-based telescopes has improved our knowledge of this kind of distant events. We present the multi-wavelength analysis of the high-zSwift GRB GRB 140515A (z = 6.327). The best estimate of the neutral hydrogen fraction of the intergalactic medium towards the burst is xHI ≤ 0.002. The spectral absorption lines detected for this event are the weakest lines ever observed in GRB afterglows, suggesting that GRB 140515A exploded in a very low-density environment. Its circum-burst medium is characterised by an average extinction (AV ~ 0.1) that seems to be typical of z ≥ 6 events. The observed multi-band light curves are explained either with a very hard injected spectrum (p = 1.7) or with a multi-component emission (p = 2.1). In the second case a long-lasting central engine activity is needed in order to explain the late time X-ray emission. The possible origin of GRB 140515A in a Pop III (or in a Pop II star with a local environment enriched by Pop III) massive star is unlikely.

Based on observations collected at the European Southern Observatory, ESO, the VLT/Kueyen telescope, Paranal, Chile (proposal code: 093.A-0069), on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofísica de Canarias (programme 49-008), and on observations made with the Italian 3.6-m Telescopio Nazionale Galileo (TNG), operated by the Fundación Galileo Galilei of the INAF (Instituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofísica de Canarias (programme A26TAC_63).Appendix A is available in electronic form at http://www.aanda.org

Volume
581
Start page
A86
Uri
Url
Issn Identifier
0004-6361
Ads BibCode
2015A&A...581A..86M
Rights
open.access
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