A model is developed here to reproduce the pulse shape of Her X-1. The 35-day cycle of pulse shape changes during the 35-day Her X-1 cycle “High – Low – Short High – Low” is caused by varying obscuration of the emission region by the accretion disk. The observed sequence of pulse shape changes imply a pencil beam from the near pole and a fan beam from the far pole. Using a newly developed code for modeling accretion column emission, including accurate treatment of gravitational light-bending effects, the observed pulse shape of Her X-1 is modeled here.

We study accretion onto the neutron star in Be/X-ray binaries, using a 3D SPH code and the data imported from a high resolution simulation by Okazaki et al. (2002) for a coplanar system with a short period (Porb = 24.3 d) and moderate eccentricity (e = 0.34). We find that a time-dependent accretion disk is formed around the neutron star in Be/X-ray binaries. The disk shrinks after the periastron passage of the Be star and restores its radius afterwards. Our simulations show that the truncated Be disk model for Be/X-ray binaries is consistent with the observed X-ray behavior.

A comparison of the XMM-Newton and Chandra Galactic Center Surveys has revealed two faint X-ray transients with contrasting properties. The X-ray spectrum of XMM J174544−2913.0 shows a strong iron line with an equivalent width of ∼2 keV, whereas that of XMM J174457−2850.3 is characterized by a very hard continuum with photon index ∼1.0. The X-ray flux of both sources varied by more than two orders of magnitude over a period of months with a peak X-ray luminosity of 5 × 1034 ergs s−1. We discuss the nature of these peculiar sources.