Hercules X-1’s light-curve dips as seen by the RXTE/PCA: a study of the entire 1996 February–2005 August light curve


E-mail: cdigna@ucalgary.ca (CDI); leahy@ucalgary.ca (DAL)


Hercules X-1 (Her X-1) light-curve dips are analysed using the entire set of Rossi X-ray Timing Explorer/Proportional Counter Array observations archived over nine years. 370 new dips are found in 35 different 35-d cycles. This is the largest record of Her X-1 dips acquired as a result of a single study and by the same satellite, and includes 20 post-eclipse recovery dips, over 100 short-high-state dips, 10 possible low-state dips, and 162 subdips, which have never been documented before. The dips were identified by X-ray energy softness ratio (SR) change. The dips’ intensity, based on SR change and derived NH, varies strongly with orbital phase. Dip duration covers a broad range: 32s–15h. The main-high-state and pre-eclipse dips are the most numerous and have the longest lengths and ingresses. There is some evidence that ingress and egress become progressively faster as the orbital cycle unfolds. Symmetry is investigated here for the first time: most dips are highly asymmetric. Duration and symmetry depend on orbital and 35-d phase. The 35-d-phase versus orbital-phase distribution is significantly different than previously reported.