SUZAKU OBSERVATIONS OF 4U 1957+11: POTENTIALLY THE MOST RAPIDLY SPINNING BLACK HOLE IN (THE HALO OF) THE GALAXY
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Nowak-2012-Suzaku observations.pdf
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Author(s)
Nowak, Michael A.
Pottschmidt, Katja
Maitra, Dipankar
Miller, Jon
Schulz, Norbert S.
Wilms, Jorn
Date Issued
December 2011
Journal
The Astrophysical Journal
Publisher
IOP Publishing
Citation
Nowak, Michael A., Jorn Wilms, Katja Pottschmidt, Norbert Schulz, Dipankar Maitra, and Jon Miller. “SUZAKU OBSERVATIONS OF 4U 1957+11: POTENTIALLY THE MOST RAPIDLY SPINNING BLACK HOLE IN (THE HALO OF) THE GALAXY.” The Astrophysical Journal 744, no. 2 (December 20, 2011): 107. © 2012 The American Astronomical Society
Version
Final published version
Abstract
We present three Suzaku observations of the black hole candidate 4U 1957+11 (V1408 Aql)—a source that exhibits some of the simplest and cleanest examples of soft, disk-dominated spectra. 4U 1957+11 also presents among the highest peak temperatures found from disk-dominated spectra. Such temperatures may be associated with rapid black hole spin. The 4U 1957+11 spectra also require a very low normalization, which can be explained by a combination of small inner disk radius and a large distance (>10 kpc) which places 4U 1957+11 well into the Galactic halo. We perform joint fits to the Suzaku spectra with both relativistic and Comptonized disk models. Assuming a low-mass black hole and the nearest distance (3 M [subscript ☉], 10 kpc), the dimensionless spin parameter a* ≡ Jc/GM [superscript 2] [> over ~] 0.9. Higher masses and farther distances yield a* ≈ 1. Similar conclusions are reached with Comptonization models; they imply a combination of small inner disk radii (or, equivalently, rapid spin) and large distance. Low spin cannot be recovered unless 4U 1957+11 is a low-mass black hole that is at the unusually large distance of [> over ~] 40 kpc. We speculate whether the suggested maximal spin is related to how the system came to reside in the halo.
MIT Department
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.1088/0004-637x/744/2/107
