15–100 keV variability in her X-1 observed by HEAO-1

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15–100 keV variability in her X-1 observed by HEAO-1

Soong, Y. / Gruber, D. / Rothschild, R.E. / Peterson, L.E.

Abstract During the 18 month mission lifetime of HEAO-1, Her X-1 was observed for 183 days of scanning by the UCSD/MIT Hard X-Ray and Low Energy Gamma-Ray Experiment, producing 14 hours of on-source livetime over five 35 day cycles. Included in this time are 13 pointed observations made at various 35 day phases, accounting for 29 hours of livetime on-source. Four complete main-ons were observed to have varying durations. Two complete short-ons and two partial short-ons were also observed. We present here results on pulse shape variations with 35 day phase as well as with energy, spectral variations with pulse phase, and pulse fractions with energy and phase. These results may indicate that the the 35d intensity profile is not due to a simple blocking mechanism at the distance of the accretion disk, and that repeatable changes in the accretion geometry near the pulse formation region may be occurring with 35d phase.