Suzaku Observations of 4U 1957+11: Potentially the Most Rapidly Spinning Black Hole in the Galaxy
Abstract
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.- Publication:
-
AAS/High Energy Astrophysics Division #12
- Pub Date:
- September 2011
- Bibcode:
- 2011HEAD...12.0107N