Spectroscopy of the short-hard GRB 130603B

The host galaxy and environment of a compact object merger^⋆

¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: adeugartepostigo@gmail.com
² Dark Cosmology Centre, Niels Bohr Institute, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
³ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
⁴ Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
⁵ Unidad Asociada Grupo Ciencia Planetarias UPV/EHU-IAA/CSIC, Departamento de Física Aplicada I, E.T.S. Ingeniería, Universidad del País-Vasco UPV/EHU, Alameda de Urquijo s/n, 48013 Bilbao, Spain
⁶ Ikerbasque, Basque Foundation for Science, Alameda de Urquijo 36-5, 48008 Bilbao, Spain
⁷ APC, Univ. Paris Diderot, CNRS/IN2P3, CEA/IRFU, Obs. de Paris, Sorbonne Paris Cité, 75205 Paris Cedex 13, France
⁸ Pontificia Universidad Católica de Chile, Departamento de Astronomía y Astrofísica, Casilla 306, 22 Santiago, Chile
⁹ Millennium Center for Supernova Science, Chile
¹⁰ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
¹¹ Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
¹² INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
¹³ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
¹⁴ ASI – Science Data Center, via Galileo Galilei, 00044 Frascati, Italy
¹⁵ INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Rome, Italy
¹⁶ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, 19 Santiago, Chile
¹⁷ Laboratoire GEPI, Observatoire de Paris, CNRS-UMR8111, Univ. Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
¹⁸ Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, 150 Reykjavik, Iceland
¹⁹ Institute of Planetary Research, DLR, Rutherfordstrasse 2, 12489 Berlin, Germany
²⁰ Dr. Karl Remeis-Observatory & ECAP, Astronomical Institute, Friedrich-Alexander University, Erlangen-Nuremberg, Sternwartstr. 7, 96049 Bamberg, Germany
²¹ Department of Astronomy, AlbaNova Science Center, Stockholm University, 106 91 Stockholm, Sweden
²² The Oskar Klein Centre, AlbaNova, 106 91 Stockholm, Sweden
²³ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA

Received: 4 November 2013
Accepted: 17 December 2013

Abstract

Context. Short duration gamma-ray bursts (SGRBs) are thought to be related to the violent merger of compact objects, such as neutron stars or black holes, which makes them promising sources of gravitational waves. The detection of a “kilonova”-likesignature associated to the Swift-detected GRB 130603B has suggested that this event is the result of a compact object merger.

Aims. Our knowledge on SGRB has been, until now, mostly based on the absence of supernova signatures and the analysis of the host galaxies to which they cannot always be securely associated. Further progress has been significantly hampered by the faintness and rapid fading of their optical counterparts (afterglows), which has so far precluded spectroscopy of such events. Afterglow spectroscopy is the key tool to firmly determine the distance at which the burst was produced, crucial to understand its physics, and study its local environment.

Methods. Here we present the first spectra of a prototypical SGRB afterglow in which both absorption and emission features are clearly detected. Together with multi-wavelength photometry we study the host and environment of GRB 130603B.

Results. From these spectra we determine the redshift of the burst to be z = 0.3565 ± 0.0002, measure rich dynamics both in absorption and emission, and a substantial line of sight extinction of A_V = 0.86 ± 0.15 mag. The GRB was located at the edge of a disrupted arm of a moderately star forming galaxy with near-solar metallicity. Unlike for most long GRBs (LGRBs), N_HX/A_V is consistent with the Galactic ratio, indicating that the explosion site differs from those found in LGRBs.

Conclusions. The merger is not associated with the most star-forming region of the galaxy; however, it did occur in a dense region, implying a rapid merger or a low natal kick velocity for the compact object binary.