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NuSTAR and Suzaku observations of the hard state in Cygnus X-1: locating the inner accretion disk

Parker, M. L. and Tomsick, J. A. and Miller, J. M. and Yamaoka, K. and Lohfink, A. and Nowak, M. and Fabian, A. C. and Alston, W. N. and Boggs, S. E. and Christensen, F. E. and Craig, W. W. and Fürst, F. and Gandhi, P. and Grefenstette, B. W. and Grinberg, V. and Hailey, C. J. and Harrison, F. A. and Kara, E. and King, A. L. and Stern, D. and Walton, D. J. and Wilms, J. and Zhang, W. W. (2015) NuSTAR and Suzaku observations of the hard state in Cygnus X-1: locating the inner accretion disk. Astrophysical Journal, 808 (1). Art. No. 9. ISSN 0004-637X. doi:10.1088/0004-637X/808/1/9.

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We present simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR ) and Suzaku observations of the X-ray binary Cygnus X-1 in the hard state. This is the first time this state has been observed in Cyg X-1 with NuSTAR, which enables us to study the reflection and broadband spectra in unprecedented detail. We confirm that the iron line cannot be fit with a combination of narrow lines and absorption features, instead requiring a relativistically blurred profile in combination with a narrow line and absorption from the companion wind. We use the reflection models of García et al. to simultaneously measure the black hole spin, disk inner radius, and coronal height in a self-consistent manner. Detailed fits to the iron line profile indicate a high level of relativistic blurring, indicative of reflection from the inner accretion disk. We find a high spin, a small inner disk radius, and a low source height and rule out truncation to greater than three gravitational radii at the 3σ confidence level. In addition, we find that the line profile has not changed greatly in the switch from soft to hard states, and that the differences are consistent with changes in the underlying reflection spectrum rather than the relativistic blurring. We find that the blurring parameters are consistent when fitting either just the iron line or the entire broadband spectrum, which is well modeled with a Comptonized continuum plus reflection model.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Parker, M. L.0000-0002-8466-7317
Tomsick, J. A.0000-0001-5506-9855
Nowak, M.0000-0001-6923-1315
Fabian, A. C.0000-0002-9378-4072
Alston, W. N.0000-0003-2658-6559
Boggs, S. E.0000-0001-9567-4224
Christensen, F. E.0000-0001-5679-1946
Fürst, F.0000-0003-0388-0560
Gandhi, P.0000-0003-3105-2615
Grefenstette, B. W.0000-0002-1984-2932
Grinberg, V.0000-0003-2538-0188
Harrison, F. A.0000-0003-2992-8024
Kara, E.0000-0003-0172-0854
Stern, D.0000-0003-2686-9241
Walton, D. J.0000-0001-5819-3552
Wilms, J.0000-0003-2065-5410
Zhang, W. W.0000-0002-1426-9698
Additional Information:© 2015 The American Astronomical Society. Received 2015 April 7; accepted 2015 May 28; published 2015 July 14. M.L.P. acknowledges financial support from the Science and Technology Facilities Council (STFC)and is grateful to Simon Gibbons for helpful discussions. J.A.T. acknowledges partial support from NASA ADAP grant NNX13AE98G. W.N.A., E.K., and A.C.F. acknowledge support from the European Union Seventh Framework Programme (FP7/2013–2017) under grant agreement no. 312789, StrongGravity. J.W. acknowledges support from Deutsches Zentrum für Luft- und Raumfahrt grant 50 OR 1411. This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). This research has made use of data obtained from the Suzaku satellite, a collaborative mission between the space agencies of Japan (JAXA) and the USA (NASA).
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
European Research Council (ERC)312789
Deutsches Zentrum fur Luft- und Raumfahrt (DLR)50 OR 1411
Subject Keywords:accretion, accretion disks – black hole physics – X-rays: binaries – X-rays: individual (Cygnus X-1)
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-52
Issue or Number:1
Record Number:CaltechAUTHORS:20150802-155802162
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59141
Deposited By: Joy Painter
Deposited On:06 Aug 2015 16:47
Last Modified:10 Nov 2021 22:15

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