The "noisy" pulsar in HER X-1.

Abstract

The results of a comparative analysis of coherent and noncoherent variations in the X-ray emission of Hercules X-1 are presented, based on Exosat archive data. In the broad band power spectrum of the source a strong noise component, variable with the 35-days cycle, is present. These changes, and the relation between the noise rms and the pulsed rms, can be interpreted as the effect of the presence of a scattering medium with variable optical depth. The results are compared with current models for the production of the noise and for the origin of the long term cycle.