A search for gamma-ray emission at energies greater than 10'1'4eV from Cygnus X-3 and eight other candidate sources.

The discovery of cosmic rays with energies greater than 1014e V has posed a question that has not, as yet, been answered: where are particles accelerated to such high energies? A possible answer to this question came in 1983 with the claim made by Samorski and Stamm of an excess number of cosmic rays from the direction of Cygnus X-3. This result was then confirmed by Lloyd-Evans et al. (1983). The excess was taken to be gamma-rays as the galactic magnetic fields result in charged particles being greatly deflected. These claims led to the birth of Pe V gamma-ray astronomy and the building of numerous instruments designed to search for point sources of Pe V gamma-ray emission. One such instrument was the GREX extensive air shower array built at Haverah Park which began collecting data in March 1986. This thesis describes the GREX array and the methods of analysis used to reconstruct the size and arrival direction of the incident cosmic rays from the detected air showers. The methods used to search for potential point sources are then described. These methods have been applied to data recorded by the GREX array between 6 March 1986 and 18 December 1990. Particular attention has been paid to Cygnus X-3 and 8 other candidate sources. No evidence for steady, periodic or sporadic emission has been found for any of the 9 potential sources. In addition, an all-sky survey has failed to discover any unknown point sources of emission in the Northern sky. Observations made by other groups of Cygnus X-3 and the 8 other candidate sources at 10 12 and 10 15 eV are discussed. Cassiday et al. (1989) claimed to have observed an excess of cosmic rays from Cygnus X-3 with energies greater than Sx10 17 eV. A claimed confirmation of this result was made by the Akeno group (Teshima et al. 1990). A search for emission of 5x10 17 eV cosmic rays from Cygnus X-3 has been made using data from the Haverah Park 12km 2 array and is described in this thesis. The upper limit to the flux from Cygnus X-3 in this search is significantly lower than the claimed flux, even during periods of contemporaneous observation