Variability in the light curve of very high energy gamma rays from Cygnus X-3

Abstract

Cygnus X-3 was observed with a new atmospheric Cerenkov technique for eight hours during October/November 1983 and for 4.5 hours during November/December 1983. A marked and significant peak is found in the 4.8 hr histogram at a phase of 0.6 in the first data set, confirming a number of previous results. A peak gamma ray flux at this phase of (5.1 + or 1.1) x 10 to the -10th photons/sq cm/s is estimated at a threshold of (8 + or - 4) x 10 to the 11th eV. Assuming a distance of 11.4 kpc, the time-averaged flux was 2.8 x 10 to the 36th ergs/s. For the November/December observations, there is no evidence for emission at any phase. This implies, with a significance of at least three sigma, variation from month-to-month which may be associated with a radio outburst.