Prompt and delayed emission properties of gamma-ray bursts observed with BeppoSAX

F. Frontera*, L. Amati, E. Costa, J. M. Muller, E. Pian, L. Piro, P. Soffitta, M. Tavani, A. Castro-Tirado, D. Dal Fiume, M. Feroci, J. Heise, N. Masetti, L. Nicastro, M. Orlandini, E. Palazzi, R. Sari

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

173 Scopus citations

Abstract

We investigated the spectral evolution in the 2-700 keV energy band of gamma-ray bursts (GRBs) detected by the Gamma-Ray Burst Monitor (GRBM) and localized with the Wide Field Cameras (WFCs) aboard the BeppoSAX satellite before 1998 May. Most of them have been followed up with the Narrow Field Instruments aboard the same satellite. In the light of these results we discuss open issues on the GRB phenomenon. We find that the optically thin synchrotron shock model (SSM) provides an acceptable representation of most of the time-resolved GRB spectra extending down to 2 keV, except in the initial phases of several bursts and during the whole duration of the quite strong GRB 970111, where a low-energy photon depletion with respect to the thin SSM spectrum is observed. A strong and time-variable low-energy cutoff, consistent with absorption effect, is observed during the prompt emission of GRB 980329. We find that the X-ray afterglow starts at about 50% of the GRB duration and that its fluence, as computed from the WFC light curve, is consistent with the decay law found from the afterglow NFI observations. We also investigate the hydrodynamical evolution of the GRB in our sample and their associated afterglow, when it was detected. We find that the photon index of the latest spectrum of the GRB prompt emission is correlated with the index of the afterglow fading law, when available, as expected on the basis of an external shock of a relativistic fireball. We also find that for most of the GRBs in our sample the late emission is consistent with a slow cooling of the shock. Adiabatic shocks appear more likely than radiative shocks. Parameters of the shocks at earliest times have been derived.

Original languageAmerican English
Pages (from-to)59-78
Number of pages20
JournalAstrophysical Journal, Supplement Series
Volume127
Issue number1
DOIs
StatePublished - Mar 2000
Externally publishedYes

Bibliographical note

Funding Information:
Disclosure: P.I. receives grant support from the National Heart, Lung, Blood Institute. All authors have no financial relationships relevant to this article to disclose.

Keywords

  • Gamma rays : Bursts
  • Gamma rays : Observations
  • Hydrodynamics
  • Shock waves
  • X-rays: General

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