The Reflection Component from Cygnus X-1 in the Soft State Measured by NuSTAR and Suzaku

John A. Tomsick, Michael A. Nowak, Michael Parker, Jon M. Miller, Andy C. Fabian, Fiona A. Harrison, Matteo Bachetti, Didier Barret, Steven E. Boggs, Finn Erland Christensen, William W. Craig, Karl Forster, Felix Fuerst, Brian W. Grefenstette, Charles J. Hailey, Ashley L. King, Kristin K. Madsen, Lorenzo Natalucci, Katja Pottschmidt, Randy R. RossDaniel Stern, Dominic J. Walton, Joern Wilms, William W. Zhang

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    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 degree 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.
    Original languageEnglish
    JournalAstrophysical Journal
    Volume780
    Issue number1
    Number of pages10
    ISSN0004-637X
    DOIs
    Publication statusPublished - 2014

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