NuSTAR AND SUZAKU OBSERVATIONS OF THE HARD STATE IN CYGNUS X-1: LOCATING THE INNER ACCRETION DISK

Journal Article · Mon Jul 20 00:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/808/1/9· OSTI ID:22522165

Parker, M. L.; Lohfink, A.; Fabian, A. C.; Alston, W. N.; Kara, E. ^[1]; Tomsick, J. A.; Boggs, S. E.; Craig, W. W. ^[2]; Miller, J. M. ^[3]; Yamaoka, K. ^[4]; Nowak, M.; Grinberg, V. ^[5]; Christensen, F. E. ^[6]; Fürst, F.; Grefenstette, B. W.; Harrison, F. A. ^[7]; Gandhi, P. ^[8]; Hailey, C. J. ^[9]; King, A. L. ^[10]; Stern, D. ^[11] ; others, and

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1. Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA (United Kingdom)
2. Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720-7450 (United States)
3. Department of Astronomy, University of Michigan, 1085 South University Avenue, West Hall 311, Ann Arbor, MI 48109-1042 (United States)
4. Solar-Terrestrial Environment Laboratory, Department of Particles and Astronomy, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan)
5. Massachusetts Institute of Technology, Kavli Institute for Astrophysics, Cambridge, MA 02139 (United States)
6. Danish Technical University, DK-2800 Lyngby (Denmark)
7. California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
8. School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom)
9. Columbia University, New York, NY 10027 (United States)
10. Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305 (United States)
11. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

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.

• OSTI ID: 22522165
• Journal Information: Astrophysical Journal, Vol. 808, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABSORPTION SPECTRA
ACCRETION DISKS
BINARY STARS
BLACK HOLES
IRON
REFLECTION
RELATIVISTIC RANGE
SPIN
STAR MODELS
TELESCOPES
X RADIATION