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

TL;DR

This study analyzes the broad iron Kalpha line in Cygnus X-1 using XMM-Newton and RXTE data, revealing relativistic effects and near-maximal black hole spin.

Contribution

First detailed analysis of the iron Kalpha line in Cygnus X-1 using modified timing mode data from XMM-Newton, combining spectral modeling with relativistic reflection.

Findings

The spectrum includes a cut-off power-law and ionized reflection.

The Fe Kalpha line is broadened by Compton and relativistic effects.

The black hole is near maximally rotating.

Abstract

We present the analysis of the broadened, flourescent iron Kalpha 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 Kalpha band. We find that the best-fit spectrum consists of the sum of an exponentially cut off power-law and relativistically smeared, ionized reflection. The shape of the broadened Fe Kalpha 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.