Probing the outer edge of an accretion disk: a Her X-1 turn-on observed with RXTE

¹ Technische Universität Darmstadt, Institut für Kernphysik, Schlossgartenstr. 9, 64289 Darmstadt, Germany e-mail: kuster@hll.mpg.de
² Max-Planck-Institut für extraterrestische Physik, Giessenbachstr., 85748 Garching, Germany
³ Department of Physics, University of Warwick, Coventry, CV7 4AL, UK
⁴ Institut für Astronomie und Astrophysik, Sand 1, 72076 Tübingen, Germany
⁵ SAIC, 16701 West Bernardo Drive, San Diego, CA 92127, USA
⁶ Center for Astrophysics and Space Sciences, UCSD, La Jolla, CA 92093, USA
⁷ Sternberg Astronomical Institute, Moscow State University, 119899 Moscow, Russia
⁸ Faculty of Physics, Moscow State University, 119899 Moscow, Russia

Received: 10 November 2004
Accepted: 29 June 2005

Abstract

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.