NuSTAR observations of the black holes GS 1354-645: Evidence of rapid black hole spin

A. M. El-Batal, J. M. Miller, M. T. Reynolds, S. E. Boggs, Finn Erland Christensen, W. W. Craig, F. Fuerst, C. J. Hailey, F. A. Harrison, D. K. Stern, J. Tomsick, D. J. Walton, W. W. Zhang

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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 = cf/GM(2) >= 0.98 (1 sigma statistical limits only). The fits also require a high inclination: 0 similar or equal to 75 (2)degrees. 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.
Original languageEnglish
Article numberL12
JournalThe Astrophysical Journal Letters
Issue number1
Number of pages5
Publication statusPublished - 2016


  • black hole physics
  • X-rays: binaries
  • Black holes
  • X-ray astronomical observations
  • Stellar rotation
  • Stellar masses
  • Stellar radiation and spectra
  • accretion
  • accretion disks
  • stellar mass
  • stellar photometry
  • stellar rotation
  • stellar spectra
  • inner accretion flow geometries
  • radial truncation
  • accretion disk
  • accretion rates
  • flared disk structures
  • X-ray light curves
  • disk reflection spectrum
  • broadband NuSTAR spectra
  • hard state outburst
  • dynamically confirmed stellar-mass black hole
  • NuSTAR study
  • rapid black hole spin
  • NuSTAR observations
  • GS 1354–645
  • astro-ph.HE

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