Search for ultra high energy radiation from gamma-ray bursts

Abstract

A recent model suggests that some gamma‐ray bursts may have photon energies as high as 10 TeV. Extensive air shower arrays could detect strong bursts with hard spectra extending above such energies. Using data from the CYGNUS array, we have searched for evidence of emission of ultra high energy (≳100 TeV) radiation coincident with gamma‐ray bursts observed either by BATSE or by the third Interplanetary Network. No statistically significant excess was found for the six bursts whose locations were accurately determined by the IPN, or for any point in the sky within 2σ of the BATSE location coordinates of an additional 52 bursts. Flux upper limits depend greatly on the zenith angle of the burst, but typical limits above 100 TeV are ∼4×10−10 cm−2 s−1. The flux upper limits for three bursts imply that the observed spectrum softens between 2 MeV and ∼100 TeV.