Precise Measurement of the Spin Parameter of the Stellar-Mass Black Hole M33 X-7

Understand

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.