An episode of ultrahigh energy radiation from the gamma -ray source Geminga: GRAPES I observations at Ooty during 1984-1987.

Abstract

A study of showers arriving from the direction of the $\ensuremath{\gamma}$-ray source Geminga (1E0630+178) has shown evidence for emission of ultrahigh energy radiation during the one week interval October 10-16, 1986. 83 showers were observed in the source bin as against an expected background of 44.1. The probability of observing this excess based on Monte Carlo simulations is less than ${10}^{\ensuremath{-}4}$. The flux observed during this period (1.00\ifmmode\pm\else\textpm\fi{}0.24)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}11}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ ${\mathrm{s}}^{\ensuremath{-}1}$ at energies \ensuremath{\ge}${10}^{14}$ eV corresponds to a time-averaged luminosity of 6\ifmmode\times\else\texttimes\fi{}${10}^{32}$ erg ${\mathrm{s}}^{\ensuremath{-}1}$.