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We performed a detailed pulse phase resolved spectroscopy of the accretingbinary X-ray pulsar Her X-1 in the energy range 3.5-75 keV and have establishedpulse phase profiles for all spectral parameters. For the centroid of thecyclotron line, the photon index and the flux of the 6.4 keV iron line, we havestudied the variation as a function of 35 d phase. We analyzed RXTEobservations of the Main-On of November 2002. Four different time intervals ofabout 1 d duration were selected to provide a good coverage of a completeMain-On. The intervals are centered at 35 d phase 0.03, 0.10, 0.15, and 0.20,respectively. All spectral parameters show a strong modulation with pulsephase. While the centroid energy of the cyclotron line follows roughly theshape of the pulse profile, both the photon index and the iron line intensityexhibit distinct minima around the peak of the X-ray pulse. With respect tovariations of the observed profiles with 35 d phase, we find that there is aclear evolution of the shape of the pulse profiles (flux versus pulse phase), amoderate increase of the maximum cyclotron line energy (found around pulsephase 0.7), but no significant evolution of the shape of the pulse phaseprofiles of the cyclotron line energy, the spectral power law index or the ironline intensity. The variation of spectral parameters as a function of the pulsephase provides important information about the system: 1. the disappearance ofthe Fe line flux near the highest continuum flux may be an indication of ahollow cone geometry of the accretion structure; ii. the apparentnon-dependence of the cyclotron line energy profiles on 35 d phase provides anew possibility to test the model of free precession of the neutron star,proposed to be responsible for the systematic variations in the pulse profiles.

Pulse phase and precession phase resolved spectroscopy of Her X-1: studying a representative Main-On with RXTE