Evidence for 10 TeV Gamma-Ray Emission from Supernova Remnants Obtained by the Tibet Air Shower Experiment

松井 康浩


   Since galactic cosmic rays are believed to be created in supernova remnants (SNRs), SNRs are expected to be a source of high energy gamma rays through the decay of neutral pions produced by {\it p-p} colitions. The characteristics of cosmic rays such as the maximum accelerated energy, spectral index and total energy SNRs can be probed by their gamma ray emission. Since the resultant gamma ray spectrum is flatter than that of the galactic background reflecting the difference of cosmic ray spectra in SNRs and in the Galaxy, SNRs are likely to be observed by gamma rays at higher energies.
   We have searched for emission of 10 TeV gamma rays from the directions of 59 SNRs located in the declination band -8.7° and 64.3°, using the data taken by the Tibet Air Shower in the period from June 1990 through Octorber of 1993. DC significances of excess events to the background are examined on each source to search for evidence of gamma ray emissions. No obvious DC excess is found from these sources. Nevertheless, when all SNRs are considered as single candidate direction, we obtained a significance of 3.59σ which corresponds to probability 1.65 × 10-4, and integral flux of 1.46 ± 0.39 - 0.29 × 10-13 cm-2s-1.