Letter to the Editor

The broad iron Kα line of Cygnus X-1 as seen by XMM-Newton in the EPIC-pn modified timing mode

¹ Dr. Karl Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Sternwartstraße 7, 96049 Bamberg, Germany
² CRESST and NASA Goddard Space Flight Center, Astrophysics Science Division, Code 661, Greenbelt, MD 20771, USA
³ Center for Space Science and Technology, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
⁴ Kavli Institute for Astrophysics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁵ Institut für Astronomie und Astrophysik, Eberhard Karls Universität Tübingen, Sand 1, 72074 Tübingen, Germany
⁶ European Space Agency, European Space Operations Centre, Robert-Bosch-Straße 5, 64293 Darmstadt, Germany
⁷ Department of Astronomy and Maryland Astronomy Center for Theory and Computation, University of Maryland, College Park, MD 20742, USA

Received: 9 June 2011
Accepted: 21 July 2011

Abstract

We present the analysis of the broadened, flourescent iron Kα line in simultaneous XMM-Newton and RXTE data from the black hole Cygnus X-1. The XMM-Newton data were taken in a modified version of the timing mode of the EPIC-pn camera. In this mode the lower energy threshold of the instrument is increased to 2.8 keV to avoid telemetry drop outs due to the brightness of the source, while at the same time preserving the signal-to-noise ratio in the Fe Kα band. We find that the best-fit spectrum consists of the sum of an exponentially cutoff power-law and relativistically smeared, ionized reflection. The shape of the broadened Fe Kα feature is due to strong Compton broadening combined with relativistic broadening. Assuming a standard, thin accretion disk, the black hole is close to rotating maximally.