New soft gamma-ray bursts in the BATSE records and spectral properties of X-ray rich bursts

Abstract

A population of X-ray dominated gamma-ray bursts (GRBs) observed by Ginga, BeppoSax and Hete-2 should be represented in the BATSE data as presumably soft bursts. We have performed a search for soft GRBs in the BATSE records in the 25--100 keV energy band. A softness of a burst spectrum can be a reason why it has been missed by the on-board procedure and previous searches for untriggered GRBs tuned to 50--300 keV range. We have found a surprisingly small number (~20/yr down to 0.1 ph cm${}^{-2}$ s${}^{-1}$) of soft GRBs where the count rate is dominated by 25--50 keV energy channel. This fact as well as the analysis of HETE-2 and common BeppoSAX/BATSE GRBs indicates that the majority of GRBs with a low Epeak has a relatively hard tail with the high-energy power-law photon index >-3. An exponential cutoff in GRB spectra below 20 keV may be a distinguishing feature separating non-GRB events.

arXiv commentSubmitted to MNRAS, 5 pages, 3 figures, 2 tables

References in corpus (5)

• The BATSE Gamma-Ray Burst Spectral Catalog. I. High Time Resolution Spectroscopy of Bright Bursts using High Energy Resolution Data
• The Fourth BATSE Gamma-Ray Burst Catalog (Revised)
• X-ray Spectral Characteristics of Ginga Gamma-Ray Bursts
• An Off-line Scan of the BATSE Daily Records and a Large Uniform Sample of Gamma-Ray Bursts
• X-Ray Light Curves of Gamma-ray Bursts Detected with the All-Sky Monitor on RXTE

Cited by in corpus (1)

• A Multivariate Fit Luminosity Function and World Model for Long GRBs