The broadband spectrum of Cygnus X-1

TL;DR

This study presents a high-quality broadband spectrum of Cygnus X-1 during a transitional state, combining data from multiple observatories to analyze the Comptonizing plasma and detect a relativistic Fe K-alpha line.

Contribution

First simultaneous broadband spectrum of Cygnus X-1 covering 3 keV to 1 MeV during a transitional state, with detailed modeling of the plasma and detection of relativistic Fe line.

Findings

Constraints on the Comptonizing plasma properties.

Detection of a relativistically broadened Fe K-alpha line.

Spectrum covering 3 keV to 1 MeV.

Abstract

The Black Hole (BH) binary Cygnus X-1 has been observed simultaneously by INTEGRAL, RXTE, and XMM-Newton for four times in November and December 2004, when Cyg X-1 became first observable with XMM-Newton. During these observations the source was found in one of its transitional states between the hard state and the soft state. We obtained a high signal to noise spectrum of Cyg X-1 from 3 keV to 1 MeV which allows us to put constraints on the nature of the Comptonizing plasma by modeling the continuum with Comptonization models as eqpair (Coppi 1992). Using XMM-Newton we were also able to confirm the presence of a relativistically broadened Fe K-alpha line.