# Spectral analysis of Swift long GRBs with known redshift

## TL;DR

This study analyzes the spectral and energetic properties of 47 Swift long GRBs with known redshift, confirming the Amati relation and exploring spectral models within Swift's limited energy range.

## Contribution

It provides a detailed spectral analysis of Swift GRBs, including error correlations and the validation of the Amati relation within Swift data, using models suited for the narrow energy range.

## Key findings

- Confirmed the Amati relation for Swift GRBs.
- Found no outliers within uncertainty limits.
- Validated spectral models against non-Swift GRB relations.

## 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.