Hercules X-1 - Pulsed gamma rays detected above 250 GeV

Abstract

The X-ray binary pulsar Hercules X-1 was observed during the spring of 1984 using the atmospheric Cherenkov technique with the Whipple Observatory 10 m reflector. Three episodes of pulsed emission, comprising about 8 percent of the total observation time, were detected at primary photons energies above 2.5 x 10 to the 11th eV. The emission occurred on time scales of a few hours or less, with possible correlations to mass-transfer episodes detected in X-rays, and to the 35 day X-ray intensity cycle. The average integral flux for the three outbursts reported here is 2.8 x 10 to the -10th/sq cm/s, implying short-term gamma-ray luminosities of over 2 x 10 to the 35th ergs/s.