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Published July 20, 2016 | Published + Submitted
Journal Article Open

NuSTAR Observations of the Black Hole GS 1354–645: Evidence of Rapid Black Hole Spin

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 a = cJ/GM^2 ⩾ 0.98 (1σ statistical limits only). The fits also require a high inclination: Θ ≃ 75(2)°. 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.

Additional Information

© 2016 The American Astronomical Society. Received 2016 May 18; revised 2016 June 30; accepted 2016 July 1; published 2016 July 19. We thank the anonymous referee for comments that improved this manuscript. This work was supported under NASA contract No. NNG08FD60C, and 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 NASA.

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Published - apjl_826_1_L12.pdf

Submitted - 1607.00343v1.pdf

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August 20, 2023
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