A BeppoSAX observation of Her X-1 during the first main-on after an anomalous low-state: Evidence for rapid spin-down

Results of a BeppoSAX observation of Her X-1 in 2000 October during the fir st main-on state after the longest recorded anomalous low-state are present ed. The 0.1-30 keV spectrum, light curve and pulse profile are all consiste nt with those measured during previous main on-states, indicating that Her X-1 has resumed its regular 35 day cycle with similar on-state properties a s before. However, from a comparison of the measured pulse period with that obtained close to the start of the anomalous low-state, it is evident that Her X-1 continued to spin-down strongly during the anomalous low-state suc h that the pulse period has returned to a similar value as similar to 15 ye ars ago. Additionally, the occurrence time of the main-on states after the end of the anomalous low-state indicate that a change in the length, or pha sing, of the 35-day cycle occurred during the anomalous low-state.