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| Paper: |
The Bimodal Distribution of Cosmic GRBs from the Data of APEX Experiment |
| Volume: |
312, Third Rome Workshop on Gamma-Ray Bursts in the Afterglow Era |
| Page: |
90 |
| Authors: |
Kozyrev, A.; Litvak, M.; Mitrofanov, I.; Sanin, A.; Barat, C.; Boer, M. |
| Abstract: |
We present a preliminary study of the duration bimodal distribution of cosmic gamma-ray bursts (GRBs) detected by the Astrophysical and Phenomenological EXperiment (APEX) onboard the Soviet Phobos-2 interplanetary spacecraft. The temporal profiles used for this analysis are recorded in the time-to-spill mode with a time resolution better than 0.1 ms. First, the emission time τ50 has been calculated for 261 short duration events which triggered the burst mode of APEX. All these events are found to have an emission time lower than 0.2 sec. The distribution of τ50 values is bimodal. The majority of events with τ50 < 2.5 ms are spike triggers which resulted from the interaction of charged particles with the APEX CsI(Tl) detector. The bulk of events with τ50 > 2.5 ms are assumed to be short GRBs. Second, considering all GRB events detected by APEX, it is found that the percentage of short bursts is about twice (58%) that obtained for BATSE. On the other hand, a very small number of short events (< 2%) is seen by LILAS, another experiment onboard the Phobos-2 spacecraft, which was sensitive to lower energies (10-300 keV). To explain all these results, a cutoff at low-energy is suggested in the spectral shape of short GRBs. |
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