Episodic emission from Hercules X-1 at energies greater than 10(14) eV: Observations with Ooty extensive air shower array during 1986

During 1986 May-July, three groups have reported detection of episodic pulsed flux from Her X-1 but with a period which was significantly smaller than the X-ray period. We have searched for similar episodes in Ooty data for 1986. Data for four days, July 1, August 8-9, and November 21, selected from days with higher than average observed shower rates, have shown evidence for flux pulsed with the same smaller period. A search for correlation between these episodes with a period precise enough to phase-lock the signal from Her X-1 has confirmed them to be related. This highly precise period, 1.2357701 s, is fully consistent with other observations during 1986. The episodic flux estimated from Ooty observations is (3.0 +/- 0.7) x 10(-11) cm(-2) s(-1) at energies > 10(14) eV. Significantly, the 1.(d)7 orbital phases for showers observed in Ooty episodes show clustering near phase of 0.65, and these episodes have all occurred near phase of 0.65 during the LOW ON state of the 35(d) cycle. A search of the Ooty data base for days with larger shower rate and at expected phase of 0.65 for 1.(d)7 and 35(d) modulation has revealed a fourth episode on 1986 December 27 which also shows the pulsar periodicity in phase with earlier episodes. These observations establish conclusively Her X-1 to be an episodic source at PeV energies.