  The compact X-ray source in the eclipsing X-ray binary IC 10 X-1 has reigned
for years as ostensibly the most massive stellar-mass black hole, with a mass
estimated to be about twice that of its closest rival. However, striking
results presented recently by Laycock et al. reveal that the mass estimate,
based on emission-line velocities, is unreliable and that the mass of the X-ray
source is essentially unconstrained. Using Chandra and NuSTAR data, we rule
against a neutron-star model and conclude that IC 10 X-1 contains a black hole.
The eclipse duration of IC 10 X-1 is shorter and its depth shallower at higher
energies, an effect consistent with the X-ray emission being obscured during
eclipse by a Compton-thick core of a dense wind. The spectrum is strongly
disk-dominated, which allows us to constrain the spin of the black hole via
X-ray continuum fitting. Three other wind-fed black-hole systems are known; the
masses and spins of their black holes are high: M ~ 10-15 Msun and a*>0.8. If
the mass of IC 10 X-1's black hole is comparable, then its spin is likewise
high.
