Article

NuSTAR OBSERVATIONS OF THE BLACK HOLE GS 1354–645: EVIDENCE OF RAPID BLACK HOLE SPIN

A. M. El-BatalDepartment of Astronomy, University of Michigan, 1085 S University Avenue, Ann Arbor, MI 48109, USA; [email protected]J. M. MillerDepartment of Astronomy, University of Michigan, 1085 S University Avenue, Ann Arbor, MI 48109, USA; [email protected]M. T. ReynoldsDepartment of Astronomy, University of Michigan, 1085 S University Avenue, Ann Arbor, MI 48109, USA; [email protected]S. E. BoggsSpace Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720-7450, USAF. E. ChistensenW. W. CraigLawrence Livermore National Laboratory, Livermore, CA 94550, USAF. FuerstCahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USAC. J. HaileyColumbia Astrophysics Laboratory and Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027, USAF. A. HarrisonCahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USADaniel SternJet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USAJohn A. TomsickSpace Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720-7450, USAD. J. WaltonJet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USAW. W. ZhangNASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

2016en

ABI

Abstract

ABSTRACT We present the results of a NuSTAR study of the dynamically confirmed stellar-mass black hole GS 1354−645. The source was observed during its 2015 “hard” state outburst; we concentrate on spectra from two relatively bright phases. In the higher-flux observation, the broadband NuSTAR spectra reveal a clear, strong disk reflection spectrum, blurred by a degree that requires a black hole spin of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>a</mml:mi> <mml:mo>=</mml:mo> <mml:mi mathvariant="italic">cJ</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi mathvariant="italic">GM</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>≥</mml:mo> <mml:mn>0.98</mml:mn> </mml:math> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1</mml:mn> <mml:mi>σ</mml:mi> </mml:math> statistical limits only). The fits also require a high inclination: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>θ</mml:mi> <mml:mo>≃</mml:mo> <mml:mn>75</mml:mn> <mml:msup> <mml:mrow> <mml:mo stretchy="true">(</mml:mo> <mml:mn>2</mml:mn> <mml:mo stretchy="true">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>◦</mml:mo> </mml:mrow> </mml:msup> </mml:math> . Strong “dips” are sometimes observed in the X-ray light curves of sources viewed at such an angle; these are absent, perhaps indicating that dips correspond to flared disk structures that only manifest at higher accretion rates. In the lower flux observation, there is evidence of radial truncation of the thin accretion disk. We discuss these results in the context of spin in stellar-mass black holes, and inner accretion flow geometries at moderate accretion rates.

Identifiers

DOI: 10.3847/2041-8205/826/1/l12

Citations and references

Cited by 30 references

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