Pre-ALMA observations of GRBs in the mm/submm range^⋆,⋆⋆

¹ Dark Cosmology Centre, Niels Bohr Institute, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
e-mail: adeugartepostigo@gmail.com
² Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
³ European Southern Observatory, Vitacura Casilla 19001, Santiago de Chile 19, Chile
⁴ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura – Santiago, Chile
⁵ Scottish Universities Physics Alliance, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ, UK
⁶ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate ( LC), Italy
⁷ Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
⁸ Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
⁹ European Southern Observatory, Karl Schwarzschild Strağe 2, 85748 Garching, Germany
¹⁰ Harvard-Smithsonian Center for Astrophysics, Submillimeter Array, 645 North A’ohoku Place, Hilo, HI 96720, USA
¹¹ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d’Hères, France
¹² Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
¹³ Herschel Science Operations Centre, INSA, ESAC, Villafranca del Castillo, 50727, 28080 Madrid, Spain
¹⁴ INAF/IASF Milano, via E. Bassini 15, 20133 Milano, Italy

Received: 8 August 2011
Accepted: 12 December 2011

Abstract

Context. Gamma-ray bursts (GRBs) generate an afterglow emission that can be detected from radio to X-rays during days, or even weeks after the initial explosion. The peak of this emission crosses the millimeter and submillimeter range during the first hours to days, making their study in this range crucial for constraining the models. Observations have been limited until now due to the low sensitivity of the observatories in this range. This situation will be greatly improved with the start of scientific operations of the Atacama Large Millimeter/submillimeter Array (ALMA).

Aims. In this work we do a statistical analysis of the complete sample of mm/submm observations of GRB afterglows obtained before the beginning of scientific operations at ALMA.

Methods. We present observations of 11 GRB afterglows obtained from the Atacama Pathfinder Experiment (APEX) and the SubMillimeter Array (SMA), as well as the first detection of a GRB with ALMA, still in the commissioning phase, and put them into context with a catalogue of all the observations that have been published until now in the spectral range that is covered by ALMA.

Results. The catalogue of mm/submm observations collected here is the largest to date and is composed of 102 GRBs, of which 88 have afterglow observations, whereas the rest are host galaxy searches. With our programmes, we contributed with data of 11 GRBs and the discovery of 2 submm counterparts. In total, the full sample, including data from the literature, has 22 afterglow detections with redshifts ranging from 0.168 to 8.2. GRBs have been detected in mm/submm wavelengths with peak luminosities spanning 2.5 orders of magnitude, the most luminous reaching 10³³erg s^-1Hz^-1. We observe a correlation between the X-ray brightness at 0.5 days and the mm/submm peak brightness. Finally we give a rough estimate of the distribution of peak flux densities of GRB afterglows, based on the current mm/submm sample.

Conclusions. Observations in the mm/submm bands have been shown to be crucial for our understanding of the physics of GRBs, but have until now been limited by the sensitivity of the observatories. With the start of the operations at ALMA, the sensitivity has improved by more than an order of magnitude, opening a new era in the study of GRB afterglows and their host galaxies. Our estimates predict that, once completed, ALMA will detect up to  ~98% of the afterglows if observed during the passage of the peak synchrotron emission.