(Cassiopeia – Spring/printemps 2017)
by Mohammed Hassan Abdallah
Thesis defended in September 2016
Department of Physics and Astronomy, University of Calgary
Thesis advisor: Dr. Dennis Leahy
We study the time dependence of the energy spectra (i.e. of the spectral model parameters, and the interpretation) of the X-ray binary system Hercules X-1/HZ Hercules (Her X-1/HZ Her) over the superorbital/35-day cycle. The results are discussed separately in two parts: one for the data during the main high state and one for the data obtained during low state and short high state. We made use of data collected by RXTE/PCA instrument in the standard-2 mode during the period from July,1996 to August of 2005 (MJD = 50290 to 53584) acquired as a result of 23 study proposals for observing the HZ Her/Her X-1 system. Observations made while the system was in anomalous low state (ALS) were removed, as the ALS are believed to be caused by a change in the status of the disc which results in disappearance of the 35-day superorbital cycle. In our data there are two anomalous low states (MJD = 51226:4 to 51756:9 & MJD = 52950:6 to 53159:4). Due to the rapid change of count rates and energy spectra during eclipse and dips periods, we remove these periods from our analysis. The main results during main high state are directly linked to the disc precession and its effect in occulting the central source and surrounding emission regions, while results obtained for the low state and short high state are related to the changing visibility of the irradiated face of HZ Her which contributes to the observed spectra by the reflected emission off of its heated face.