Search for ultrashort gamma-ray bursts from evaporating primordial black holes

Cosmic gamma-ray bursts from evaporating primordial black holes for the evaporation model with relativistic phase transitions have been sought in the data from the Andyrchy extensive air shower (EAS) array. This model predicts ultrashort (${\simeq}\,10^{-13}$ s) gamma-ray bursts with the spectrum with the maximum intensities simultaneously at the photon energies of $100$ MeV and $100$ GeV. Such ultrashort gamma-ray bursts can be detected by EAS arrays located on mountains as EASs with a uniform lateral distribution. A limit on the concentration of evaporating primordial black holes in a local region of the Galaxy for this evaporation model has been obtained from information accumulated during a live time of $4.23$ yr.