0520028

We propose INTEGRAL observations of theaccreting binary X-ray pulsar Her X-1 for a total of 460 ks in its Main-On state. The main goal is to answer a number of fundamental questions related to the class of accreting binary X-ray pulsars e.g.: Is the neutron star in Her X-1 indeed precessing freely? and What isthe exact physics in the magnetized accretion column generating spectra with cyclotron lines?We propose to study systematic variations with time and with precessional phase of the cyclotron line feature the hard X-ray pulse profile and the pulse period. Such observations will exploit two unique features of INTEGRAL: its excellent energy and time resolution and the capability toperform long uninterrupted observations. [truncated! Please see actual data for full text]