Evidence for pulsed emission from the Crab pulsar at PeV energies: Ooty observations during 1984-87

Abstract

Ooty database consisting of nearly 7 million air showers of energies > 2 10¹⁴ eV collected during 1984-87 has been analyzed for detection of emission of ultra high energy radiation from the Crab pulsar and nebula. No significant time-averaged excess has been observed from the direction of the Crab pulsar/nebula. However, a search of these data for pulsed flux has yielded significant evidence for emission which is time-coincident in phase with the optical interpulse in the light curve of the Crab pulsar, PSR 0531 + 21. The pulsed flux is nearly constant with time over the three years of observations. Data also show that the average age of the showers ascribed to pulsed flux from the Crab pulsar is larger. These observations correspond to a time-averaged pulsed flux of (4.1 ± 1.2) 10^-13 cm^-2 s^-1 from the Crab pulsar at energies > 2 10¹⁴ eV.