The BeppoSAX catalog of GRB X-ray afterglow observations

¹ INAF Rome, via fosso del cavaliere 100, 00133 Roma, Italy e-mail: mdp@mssl.ucl.ac.uk; [luigi.piro;bruce.gendre;enrico.costa;marco.feroci;paolo.soffitta]@.iasf-roma.inaf.it
² Mullard Space Science Laboratory, University College of London, Holmbury St. Mary, Dorking, RH5 6NT, UK
³ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, via P. Gobetti 101, 40219 Bologna, Italy e-mail: amati@bo.iasf.cnr.it
⁴ Rome Astronomical Observatory, via di Frascati 33, 00044 Rome, Italy e-mail: a.antonelli@mporzio.astro.it
⁵ Università di Ferrara, via Paradiso 12, 44100 Ferrara, Italy e-mail: frontera@fe.infn.it
⁶ Istituto Astrofisica Spaziale e Fisica Cosmica, Sezione di Palermo, INAF, via U. La Malfa 153, 90146 Palermo, Italy e-mail: nicastro@pa.iasf.cnr.it
⁷ Space Research Organization of the Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands e-mail: jeanz@sron.nl

Received: 29 July 2005
Accepted: 18 March 2006

Abstract

We present the catalog of X-ray afterglow observed by BeppoSAX from the launch of the satellite to the end of the mission. Thirty-three X-ray afterglows out of 39 observations were securely identified based on their fading behavior. We have extracted the continuum parameters (decay index, spectral index, flux, absorption) for all available afterglows. We point out a possible correlation between the X-ray afterglow luminosity and the energy emitted during the prompt γ-ray event. We do not detect a significant jet signature within the afterglows, implying a lower limit on the beaming angle, nor a standard energy release when X-ray fluxes are corrected for beaming. Our data support the hypothesis that the burst should be surrounded by an interstellar medium rather than a wind environment, and that this environment should be dense. This may be explained by a termination shock located near the burst progenitor. We finally point out that some dark bursts may be explained by an intrinsic faintness of the event, while others may be strongly absorbed.