Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-03-12
The Astrophysical Journal, 679, L37-L40, 2008 May 20
Astronomy and Astrophysics
Astrophysics
14 pages, 3 figures, 1 table, published in ApJ Letters; as explained in the erratum at the end of the text, the spin parameter
Scientific paper
10.1086/588840
In prior work, {\it Chandra} and Gemini-North observations of the eclipsing X-ray binary M33 X-7 have yielded measurements of the mass of its black hole primary and the system's orbital inclination angle of unprecedented accuracy. Likewise, the distance to the binary is known to a few percent. In an analysis based on these precise results, fifteen {\it Chandra} and {\it XMM-Newton} X-ray spectra, and our fully relativistic accretion disk model, we find that the dimensionless spin parameter of the black hole primary is $a_* = 0.77 \pm 0.05$. The quoted 1-$\sigma$ error includes all sources of observational uncertainty. Four {\it Chandra} spectra of the highest quality, which were obtained over a span of several years, all lead to the same estimate of spin to within statistical errors (2%), and this estimate is confirmed by 11 spectra of lower quality. There are two remaining uncertainties: (1) the validity of the relativistic model used to analyze the observations, which is being addressed in ongoing theoretical work; and (2) our assumption that the black hole spin is approximately aligned with the angular momentum vector of the binary, which can be addressed by a future X-ray polarimetry mission.
Davis Shane W.
Liu Jifeng
McClintock Jeffery E.
Narayan Ramesh
Orosz Jerome A.
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