Suzaku Observations of 4U 1957+11: Potentially the Most Rapidly Spinning Black Hole in the Galaxy

Details Suzaku Observations of 4U 1957+11: Potentially the Most Rapidly Spinning Black Hole in the Galaxy Suzaku Observations of 4U 1957+11: Potentially the Most Rapidly Spinning Black Hole in the Galaxy

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011head...12.0107n&link_type=abstract

American Astronomical Society, HEAD meeting #12, #1.07

Astronomy and Astrophysics

Astronomy

Scientific paper

We present three Suzaku observations of the black hole candidate 4U1957+11 --- a source that exhibits some of the cleanest examples of disk-dominated spectra and presents among the highest peak temperatures found from such spectra. High temperatures may be associated with rapid black hole spin. These spectra also require a very low normalization, which can be explained by a combination of small inner disk radius, and large distance (>10 kpc), which places 4U1957+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 solar masses, 10 kpc), the dimensionless spin parameter a* > 0.9 Jc/GM2. Higher masses and farther distances yield a* 1. Similar conclusions are reached with Comptonization models. Low spin cannot be recovered unless 4U1957+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.
This work was supported by NASA Grants NNX10AR94G and SV3-73016.

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