Revealing the broad iron Kα line in Cygnus X-1 through simultaneous XMM-Newton, RXTE, and INTEGRAL observations

¹ Dr. Karl Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Sternwartstraße 7, 96049 Bamberg, Germany
e-mail: joern.wilms@sternwarte.uni-erlangen.de
² AIT Austrian Institute of Technology GmbH, Donau-City-Straße 1, 1220 Vienna, Austria
³ Kavli Institute for Astrophysics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴ Laboratoire AIM, CEA/IRFU-Université Paris Diderot-CNRS/INSU, CEA DSM/IRFU/SAp, Centre de Saclay, 91191 Gif-sur-Yvette, France
⁵ Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720, USA
⁶ CRESST and NASA Goddard Space Flight Center, Astrophysics Science Division, Code 661, Greenbelt, MD 20771, USA
⁷ Center for Space Science and Technology, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
⁸ Institut für Astronomie und Astrophysik, Eberhard Karls Universität Tübingen, Sand 1, 72074 Tübingen, Germany
⁹ Max Planck Computing and Data Facility, Gießenbachstraße 2, 85748 Garching, Germany
¹⁰ Department of Chemistry, Physics, and Astronomy, Georgia College, CBX 082, Milledgeville, GA 31061, USA
¹¹ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
¹² Department of Astronomy and Maryland Astronomy Center for Theory and Computation, University of Maryland, College Park, MD 20742, USA
¹³ European Space Agency, European Space Operations Centre, Robert-Bosch-Straße 5, 64293 Darmstadt, Germany

Received: 4 August 2014
Accepted: 20 February 2016

Abstract

We report on the analysis of the broad Fe Kα line feature of Cyg X-1 in the spectra of four simultaneous hard intermediate state observations made with the X-ray Multiple Mirror mission (XMM-Newton), the Rossi X-ray Timing Explorer (RXTE), and the International Gamma-Ray Astrophysics Laboratory (INTEGRAL). The high quality of the XMM-Newton data taken in the Modified Timing Mode of the EPIC-pn camera provides a great opportunity to investigate the broadened Fe Kα reflection line at 6.4 keV with a very high signal to noise ratio. The 4–500 keV energy range is used to constrain the underlying continuum and the reflection at higher energies. We first investigate the data by applying a phenomenological model that consists of the sum of an exponentially cutoff power law and relativistically smeared reflection. Additionally, we apply a more physical approach and model the irradiation of the accretion disk directly from the lamp post geometry. All four observations show consistent values for the black hole parameters with a spin of a ~ 0.9, in agreement with recent measurements from reflection and disk continuum fitting. The inclination is found to be i ~ 30°, consistent with the orbital inclination and different from inclination measurements made during the soft state, which show a higher inclination. We speculate that the difference between the inclination measurements is due to changes in the inner region of the accretion disk.