Intrinsic spectra and energetics of BeppoSAX Gamma–Ray Bursts with known redshifts

¹ Istituto di Astrofisica Spaziale e Fisica cosmica – Sezione di Bologna, CNR, Via Gobetti 101, 40129 Bologna, Italy
² Dipartimento di Fisica, Università di Ferrara, Via Paradiso 12, 44100 Ferrara, Italy
³ Istituto di Astrofisica Spaziale e Fisica cosmica – Sezione di Milano, CNR, Via Bassini 15, 20133 Milano, Italy
⁴ Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁵ Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monteporzio Catone (RM), Italy
⁶ Istituto di Astrofisica Spaziale e Fisica cosmica, CNR, Via Fosso del Cavaliere, 00133 Roma, Italy
⁷ Istituto di Astrofisica Spaziale e Fisica cosmica – Sezione di Palermo, CNR, Via La Malfa 153, 90146 Palermo, Italy
⁸ Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131, Trieste, Italy

Corresponding author: L. Amati, amati@tesre.bo.cnr.it

Received: 6 February 2001
Accepted: 15 May 2002

Abstract

We present the main results of a study of spectral and energetics properties of twelve gamma-ray bursts (GRBs) with redshift estimates. All GRBs in our sample were detected by BeppoSAX in a broad energy range (2–700 ). From the redshift estimates and the good-quality BeppoSAX time–integrated spectra we deduce the main properties of GRBs in their cosmological rest frames. All spectra in our sample are satisfactorily represented by the Band model, with no significant soft X–ray excesses or spectral absorptions. We find a positive correlation between the estimated total (isotropic) energies in the 1–10 000 energy range (E_rad) and redshifts z. Interestingly, more luminous GRBs are characterized also by larger peak energies E_ps of their spectra. Furthermore, more distant GRBs appear to be systematically harder in the X–ray band compared to GRBs with lower redshifts. We discuss how selection and data truncation effects could bias our results and give possible explanations for the correlations that we found.