Her X-1: Modelling the Anomalous and Preeclipse Dips with the Coronal Wind Model

The interaction between the accretion stream and the thin, tilted and twisted accretion disk is found to be consistent with the observed complex dip structure in the X-ray signal of Her X-1. The stream falls into the warped disk mostly from above or below where the hydrodynamic interaction leads to a cold clumpy spray covering the X-ray source once per orbit. We test this model with the warped disk shape obtained from coronal wind torques and get the correct phases for the observed preeclipse dips. This includes the peculiar “marching backwards” in orbital phase with the proceeding 35 day period. The penetration of the stream further results in a turbulent thickening of the disk rings at the involved radii which last for the dynamical timescale which is of the order of the Kepler period. At turn-on the observer looks marginally over a particular region of the disk surface. Now, at orbital phases where this is thickened, it will cover the X-ray source again producing an anomalous dip. Later in the 35 day period the observer looks far over the disk and its temporal thickening. This occurs twice per orbit and the simulated phases agree with the observed times. – Because these dips and the turn-on are both caused by the disk the turn-on always takes place at the same orbital phases reproducing the observations.