Average 2 - 6 keV pulse shapes of Hercules X-1 during the January 1972 "on" state.

The available data on the Uhuru satellite sightings of observably bright ('on' state) Her X-1 during January 1972 are divided into eight intervals between successive eclipses. The average pulse shapes obtained are discussed. It is shown that the average pulse shape varies little during most of the 'on' state. However, during about the last three days of the 'on' state, the pulsations almost completely disappear. The results appear to support a class of models in which the 35-day cycle is due to variable obscuration of Her X-1 by a precessing accretion disk or other matter within the system.