  We present the analysis of Rossi X-ray Timing Explorer (RXTE) observations of
the turn-on phase of a 35 day cycle of the X-ray binary Her X-1. During the
early phases of the turn-on, the energy spectrum is composed of X-rays
scattered into the line of sight plus heavily absorbed X-rays. The energy
spectra in the 3-17 keV range can be described by a partial covering model,
where one of the components is influenced by photoelectric absorption and
Thomson scattering in cold material plus an iron emission line at 6.5 keV. In
this paper we show the evolution of spectral parameters as well as the
evolution of the pulse profile during the turn-on. We describe this evolution
using Monte Carlo simulations which self-consistently describe the evolution of
the X-ray pulse profile and of the energy spectrum.
