We present a Chandra and HST study of IC 10 X-1 , the most luminous X-ray binary in the closest starburst galaxy to the Milky Way .
Our new hard X-ray observation of X-1 confirms that it has an average 0.5–10 keV luminosity of 1.5 \times 10 ^ { 38 } erg s ^ { -1 } , is strongly variable ( a factor of \approx 2 in \lesssim 3 ks ) , and is spatially coincident ( within 0 \farcs 23 \pm 0 \farcs 30 ) with the Wolf-Rayet ( WR ) star [ MAC92 ] 17A in IC 10 .
The spectrum of X-1 is best fit by a power law with \Gamma \approx 1.8 and a thermal plasma with kT \approx 1.5 keV , although systematic residuals hint at further complexity .
Taken together , these facts suggest that X-1 may be a black hole belonging to the rare class of WR binaries ; it is comparable in many ways to Cyg X-3 .
The Chandra observation also finds evidence for extended X-ray emission co-spatial with the large non-thermal radio superbubble surrounding X-1 .