Spectral analysis of Swift long GRBs with known redshift

Abstract

We study the spectral and energetics properties of 47 long-duration gamma-ray bursts (GRBs) with known redshift, all of them detected by the Swift satellite. Due to the narrow energy range (15-150 keV) of the Swift-BAT detector, the spectral fitting is reliable only for fitting models with 2 or 3 parameters. As high uncertainty and correlation among the errors is expected, a careful analysis of the errors is necessary. We fit both the power law (PL, 2 parameters) and cut--off power law (CPL, 3 parameters) models to the time-integrated spectra of the 47 bursts, and present the corresponding parameters, their uncertainties, and the correlations among the uncertainties. The CPL model is reliable only for 29 bursts for which we estimate the nuf_nu peak energy Epk. For these GRBs, we calculate the energy fluence and the rest- frame isotropic-equivalent radiated energy, Eiso, as well as the propagated uncertainties and correlations among them. We explore the distribution of our homogeneous sample of GRBs on the rest-frame diagram E'pk vs Eiso. We confirm a significant correlation between these two quantities (the "Amati" relation) and we verify that, within the uncertainty limits, no outliers are present. We also fit the spectra to a Band model with the high energy power law index frozen to -2.3, obtaining a rather good agreement with the "Amati" relation of non-Swift GRBs.

16 pages. To appear in MNRAS. Minor changes were introduced in this last version

References in corpus (3)

• Gamma-Ray Bursts: Progress, Problems & Prospects
• The Hubble Diagram to Redshift >6 from 69 Gamma-Ray Bursts
• Variation of the Amati Relation with the Cosmological Redshift: a Selection Effect or an Evolution Effect?

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• Low-Luminosity Gamma-Ray Bursts as a Distinct GRB Population:A Firmer Case from Multiple Criteria Constraints
• The Epeak-Eiso plane of long Gamma Ray Bursts and selection effects
• Global Properties of X-Ray Flashes and X-Ray-Rich Gamma-Ray Bursts Observed by Swift
• Peak energy of the prompt emission of long Gamma Ray Bursts vs their fluence and peak flux
• Generalized Tests for Selection Effects in GRB High-Energy Correlations
• Time-resolved spectral correlations of long-duration Gamma-Ray Bursts
• Hubble Diagram of Gamma-Rays Bursts calibrated with Gurzadyan-Xue Cosmology
• Factor analysis of the long gamma-ray bursts
• Synchrotron Self-Absorption Process in GRBs and the Isotropic Energy - Peak Energy Fundamental Relation