Ultra high energy gamma rays from CYG X-3.

The variability of the ultra high energy (UHE) gamma-ray intensity of Cygnus X3 on a time scale of 4.8 h is analyzed based on observations using the Dugway gamma-ray telescopes. Results of drift scan observations show evidence for a 4.8 h modulation which indicates that UHE gamma-rays of greater than 1300 GeV energy are emitted with an average peak strength of about 2 x 10 to the -10th/sq-sec, with the maximum in gamma rays coinciding with the X-ray maximum. The temporal profiles of the 4.8 h maxima show that the peak activity is confined to intervals of a few minutes close to X-ray phase 0.625. In addition, a 34 d variation in the strength of the 4.8 h maximum is observed in the UHE gamma rays. It is found that, at times of maximum activity, the telescope of maximum sensitivity (threshold 1000 GeV) detects a flux of 2 x 10 to the -9th/sq cm-sec.