Evolution of spectral parameters during a pre-eclipse dip of Her X-1
  We report on a pre-eclipse dip of the X-ray binary Her X-1 observed by the Rossi X-ray Timing Explorer (RXTE) in July 1996. We present the evolution of the spectral parameters in the 3-18 keV range with a temporal resolution of 16 s and show that the varying flux of the spectrum can be interpreted solely by a time varying column density. We also find that the lightcurve is characterized by symmetric substructures with recurrence time of a few minutes that can be successfully modeled by Gaussian profiles. 
B. Stelzer (1,2), J. Wilms (1), R. Staubert (1), D. Gruber (3), R.   Rothschild (3) ((1) Institut fuer Astronomie und Astrop...