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

Yana Tikhomirova·Boris Stern·Alexandra Kozyreva·Juri Poutanen
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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.

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Yana Tikhomirova, Boris Stern, Alexandra Kozyreva, Juri Poutanen. 2005-10-07. New soft gamma-ray bursts in the BATSE records and spectral properties of X-ray rich bursts. https://doi.org/10.1111/j.1365-2966.2006.10047.x

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