A study of the prompt and afterglow emission of the short GRB 061201^*

¹ ASI Science Data Center, via Galileo Galilei, 00044 Frascati, Italy (INAF personnel resident at ASDC.) e-mail: giulia.stratta@asdc.asi.it
² Università degli Studi dell'Insubria, Dipartimento di Fisica e Matematica, via Valleggio 11, 22100 Como, Italy
³ INAF - Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
⁴ INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
⁵ Università di Perugia, Dipartimento di fisica, Viale A. Pascoli, 06123 Perugia, Italy
⁶ Università degli studi di Roma “La Sapienza”, Piazzale Aldo Moro 2, 00185 Roma, Italy
⁷ Astrophysics Science Division, Code 660.1, NASA/GSFC, Greenbelt, MD 20770, USA
⁸ Universities Space Research Association, 10227, Wincopin Circle, Suite 221, Columbia, MS 21044, USA
⁹ Università degli Studi di Milano, Bicocca, Piazza delle Scienze 3, 20126 Milano, Italy
¹⁰ INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Sezione di Palermo, via Ugo la Malfa 153, 90146 Palermo, Italy
¹¹ Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
¹² Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, UK

Received: 4 June 2007
Accepted: 22 August 2007

Abstract

Context. Our knowledge of the intrinsic properties of short duration Gamma-Ray Bursts has relied, so far, only upon a few cases for which the estimate of the distance and an extended, multiwavelength monitoring of the afterglow have been obtained.

Aims. We carried out multiwavelength observations of the short GRB 061201 aimed at estimating its distance and studying its properties.

Methods.We performed a spectral and timing analysis of the prompt and afterglow emission and discuss the results in the context of the standard fireball model.

Results. A clear temporal break was observed in the X-ray light curve about 40 min after the burst trigger. We find that the spectral and timing behaviour of the X-ray afterglow is consistent with a jet origin of the observed break, although the optical data can not definitively confirm this and other scenarios are possible. No underlying host galaxy down to R ~ 26 mag was found after fading of the optical afterglow. Thus, no secure redshift could be measured for this burst. The nearest galaxy is at and shows evidence of star formation activity. We discuss the association of GRB 061201 with this galaxy and with the ACO S 995 galaxy cluster, from which the source is at an angular distance of 17'' and 8.5', respectively. We also test the association with a possible undetected, positionally consistent galaxy at z ~ 1. In all these cases, in the jet interpretation, we find a jet opening angle of 1–2 degrees.