The 35-d X-ray profile of Her X-1

FOLLOWING the report from Ariel V (ref. 1) of substantial X-ray emission from Her X-1 midway through the extended low-state portion of its 35-d cycle, Jones and Forman² have reported a similar feature during another cycle, measured from Uhuru. They further suggest that this feature should occur regularly, consistent with models for the mass accretion disk which are inclined with respect to the binary orbital plane^3,4. We report here the results of the analysis of > 500 d of Ariel V all-sky monitor (ASM) data, which support the view that the feature occurs regularly in the 35-d cycle.