2012ApJ...744..107N -
Astrophys. J., 744, 107 (2012/January-2)
Suzaku observations of 4U 1957+11: potentially the most rapidly spinning black hole in (the halo of) the Galaxy.
NOWAK M.A., WILMS J., POTTSCHMIDT K., SCHULZ N., MAITRA D. and MILLER J.
Abstract (from CDS):
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☉, 10 kpc), the dimensionless spin parameter a* ≡ Jc/GM 2 ≳ 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 ≳ 40 kpc. We speculate whether the suggested maximal spin is related to how the system came to reside in the halo.
Abstract Copyright:
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Journal keyword(s):
accretion, accretion disks - black hole physics - radiation mechanisms: thermal - X-rays: binaries
Simbad objects:
4
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