The Reflection Component from Cygnus X-1 in the Soft State Measured by NuSTAR and Suzaku
Hailey, Charles J.; Fürst, Felix; Pottschmidt, Katja; Wilms, Jörn; Walton, Dominic J.; Miller, Jon M.; Stern, Daniel; Madsen, Kristin K.; Parker, Michael; Boggs, Steven E.; Harrison, Fiona A.; Christensen, Finn E.; Craig, William W.; Forster, Karl; Grefenstette, Brian W.; Zhang, William W.; Tomsick, John A.; Bachetti, Matteo; Natalucci, Lorenzo; Nowak, Michael A.; Barret, Didier; King, Ashley L.; Fabian, Andy C.; Ross, Randy R.
United States, United Kingdom, France, Denmark, Italy, Germany
Abstract
The black hole binary Cygnus X-1 was observed in late 2012 with the Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku, providing spectral coverage over the ~1-300 keV range. The source was in the soft state with a multi-temperature blackbody, power law, and reflection components along with absorption from highly ionized material in the system. The high throughput of NuSTAR allows for a very high quality measurement of the complex iron line region as well as the rest of the reflection component. The iron line is clearly broadened and is well described by a relativistic blurring model, providing an opportunity to constrain the black hole spin. Although the spin constraint depends somewhat on which continuum model is used, we obtain a * > 0.83 for all models that provide a good description of the spectrum. However, none of our spectral fits give a disk inclination that is consistent with the most recently reported binary values for Cyg X-1. This may indicate that there is a >13° misalignment between the orbital plane and the inner accretion disk (i.e., a warped accretion disk) or that there is missing physics in the spectral models.