SIMBAD references

Here the set of Ginga observations of Hercules X-1 are analyzed. Light curves and softness ratios are used to characterize spectral shape changes which occur during the 35-day cycle of Her X-1. Evidence for spectral changes in the high and short-on states is given. The low state is significantly harder in both colors than the high state, the short-on state significantly softer. High state dips follow a locus in the color-color diagram, which is shared also by eclipse ingresses and high state turn off. The same events in the short-on state follow a similar locus, but the locus is shifted to softer colors, which can be explained by a larger component of scattered radiation.