A Search for Hard‐Spectrum Gamma‐Ray Bursts UsingSMM

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Abstract
We have searched over 9 yr of data from the Solar Maximum Mission (SMM) Gamma Ray Spectrometer for gamma-ray bursts (GRBs) with abnormally hard spectra that may have been missed in previous searches in the 0.35-0.8 MeV energy band. For this purpose, we searched the higher 0.8-10 MeV band. We have found only two new GRBs in this search, compared to 177 GRBs found in the 0.35-0.8 MeV band. We have made a careful examination of the threshold conditions for identifying the 0.8-10 MeV events, which confirms that there is no undiscovered population of hard-spectrum GRBs that have escaped detection by SMM, BATSE, and other instruments triggered by low-energy γ-ray emission. This conclusion does not apply to GRBs with duration less than 2 s, nor to those that are much fainter than the general population. Our results constrain models of GRBs that require or allow the peak in energy emission to be above 1 MeV.