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 nu F(nu) 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 similar to 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 approximate to 15 keV. The T(90,rest) distribution of long GRBs peaks at similar to 10 s. The distribution of E(iso) has mean and median values of 8.9 x 10(52) erg and 8.2 x 10(52) 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 a 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).

Rest-frame properties of 32 Gamma-Ray Bursts observed by the Fermi Gamma-ray Burst Monitor

BISSALDI, ELISABETTA;
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 nu F(nu) 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 similar to 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 approximate to 15 keV. The T(90,rest) distribution of long GRBs peaks at similar to 10 s. The distribution of E(iso) has mean and median values of 8.9 x 10(52) erg and 8.2 x 10(52) 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 a 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).
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11368/2749138
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