Rest-frame properties of 32 gamma-ray bursts observed by the Fermi Gamma-ray Burst Monitor

¹ Max Planck Institute for extraterrestrial Physics, Giessenbachstrasse 1, 85748, Garching, Germany
e-mail: dgruber@mpe.mpg.de
² University of Alabama in Huntsville, NSSTC, 320 Sparkman Drive, Huntsville, AL 35805, USA
³ University College, Dublin, Belfield, Stillorgan Road, Dublin 4, Ireland
⁴ Space Science Office, VP62, NASA/Marshall Space Flight Center Huntsville, AL 35812, USA
⁵ Jacobs Technology, Inc., Huntsville, Alabama
⁶ Los Alamos National Laboratory, PO Box 1663, Los Alamos, NM 87545, USA
⁷ Universities Space Research Association, NSSTC, 320 Sparkman Drive, Huntsville, AL 35805, USA

Received: 24 March 2011
Accepted: 23 April 2011

Abstract

Aims. In this paper we study the main spectral and temporal properties of gamma-ray bursts (GRBs) observed by Fermi/GBM. We investigate these key properties of GRBs in the rest-frame of the progenitor and test for possible intra-parameter correlations to better understand the intrinsic nature of these events.

Methods. Our sample comprises 32 GRBs with measured redshift that were observed by GBM until August 2010. 28 of them belong to the long-duration population and 4 events were classified as short/hard bursts. For all of these events we derive, where possible, the intrinsic peak energy in the νF_ν spectrum (E_p,rest), the duration in the rest-frame, defined as the time in which 90% of the burst fluence was observed (T_90,rest) and the isotropic equivalent bolometric energy (E_iso).

Results. The distribution of E_p,rest has mean and median values of 1.1 MeV and 750 keV, respectively. A log-normal fit to the sample of long bursts peaks at  ~800 keV. No high-E_p population is found but the distribution is biased against low E_p values. We find the lowest possible E_p that GBM can recover to be  ≈ 15 keV. The T_90,rest distribution of long GRBs peaks at  ~10 s. The distribution of E_iso has mean and median values of 8.9  ×  10⁵² erg and 8.2  ×  10⁵² erg, respectively. We confirm the tight correlation between E_p,rest and E_iso (Amati relation) and the one between E_p,rest and the 1-s peak luminosity (L_p) (Yonetoku relation). Additionally, we observe a parameter reconstruction effect, i.e. the low-energy power law index α gets softer when E_p is located at the lower end of the detector energy range. Moreover, we do not find any significant cosmic evolution of neither E_p,rest nor T_90,rest.