Detection of the high GRB 080913 and its implications on progenitors and energy extraction mechanisms ^*

¹ Departamento de Física, Universidad de Jaén, Campus Las Lagunillas, 23071 Jaén, Spain e-mail: dperez@ujaen.es
² Department of Physics and Astronomy, The University of Leicester, Leicester, LE1 7RH, UK

³ European Southern Observatory, Casilla 19001, Santiago 19, Chile

⁴ Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 3.004, 18.080 Granada, Spain

⁵ Departamento de Astronomía y Astrofísica, Universidad de Valencia, C/ Dr. Moliner s/n, 46100 Burjassot, Valencia, Spain

⁶ Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
⁷ Dept. of Physics, Bolyai Military University, POB 15, 1581 Budapest, Hungary
⁸ Dept. of Physics of Complex Systems, Eötvös University, Pázmány P. s. 1/A, 1117 Budapest, Hungary
⁹ Edif. Institutos de Investigación (GACE-ICMOL), Universidad de Valencia, Campus de Paterna, 46980 Paterna, Valencia, Spain

¹⁰ Nikolaev State University, Nikolskaya 24, 54030 Nikolaev, Ukraine 

¹¹ Institute de Radioastronomie Milimétrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d'Héres, France
¹² INAF - Osservatorio Astronomico di Brera, Via Emilio Bianchi, 46, Merate, LC, 23807, Italy

Received: 14 October 2008
Accepted: 14 December 2009

Abstract

Aims. We present multiwavelength observations of one of the most distant gamma-ray bursts detected so far, GRB 080913. Based on these observations, we consider whether it could be classified as a short-duration GRB and discuss the implications for the progenitor nature and energy extraction mechanisms.

Methods. Multiwavelength X-ray, near IR and millimetre observations were made between 20.7 h and ~16.8 days after the event.

Results. Whereas a very faint afterglow was seen at the 3.5m CAHA telescope in the nIR, the X-ray afterglow was clearly detected in both Swift and XMM-Newton observations. An upper limit is reported in the mm range. We have modeled the data assuming a collimated ≳ 3° blast wave with an energy injection at days carrying erg or approximately 12 times the initial energy of the blast wave. We find that GRB 080913 shares many of the gamma-ray diagnostics with the more recent burst GRB 090423 for being classified as short had they ocurred at low redshift. If the progenitor were a compact binary merger, it is likely composed by a NS and BH. The Blandford-Znajek (BZ) mechanism is the preferred one to extract energy from the central, maximally-rotating BH. Both the magnetic field close to the event horizon (B) and the BH mass () are restricted within a relatively narrow range, such that . Similar constraints on the central BH hold for collapsar-like progenitor systems if the BZ-mechanism works for the system at hand.