A Model for the Accretion Disk of Hercules X-1 from 35-Day Cycle Lightcurves

The 35-day X-ray lightcurve of Hercules X-1 consists of a Main High state, a Short High state and two Low states. These are caused by a precessing tilted and twisted accretion disk. The best available 35-day average lightcurves are from Swift/BAT observations in the 15-50 keV band and from MAXI observations in the 2-20 keV band. The current work fits the 35-day X-ray lightcurve from Swift/BAT and fits the MAXI 35-day X-ray lightcurve using a disk plus corona model. The parameters of the disk and its corona from the two data sets are consistent with eachother. The fit of two different data sets with the same model verifies the reliabilty of the disk plus corona model and its parameter values. We find the inner corona radius is significantly smaller than the inner disk radius, consistent with the conclusions of pulse shape studies. The system inclination of $85.12\pm0.24^{\circ}$ is consistent with the recent value derived from MAXI observations alone, and much improved compared to earlier estimates ($\sim$82 to 88$^\circ$). This results is significantly improved binary system parameters, including neutron star mass, companion mass and companion radius.