A report is presented on Suzaku observations of the ultra-luminous X-ray source X-1 in the starburst galaxy M82 , made three time in 2005 October for an exposure of \sim 30 ks each .
The XIS signals from a region of radius 3 ^ { \prime } around the nucleus defined a 2–10 keV flux of 2.1 \times 10 ^ { -11 } erg s ^ { -1 } cm ^ { -2 } attributable to point sources .
The 3.2–10 keV spectrum was slightly more convex than a power-law with a photon index of 1.7 .
In all observations , the HXD also detected signals from M82 up to \sim 20 keV , at a 12–20 keV flux of 4.4 \times 10 ^ { -12 } erg s ^ { -1 } cm ^ { -2 } .
The HXD spectrum was steeper than that of the XIS .
The XIS and HXD spectra can be jointly reproduced by a cutoff power-law model , or similar curved models .
Of the detected wide-band signals , 1/3 to 2/3 are attributable to X-1 , while the remainder to other discrete sources in M82 .
Regardless of the modeling of these contaminants , the spectrum attributable to X-1 is more curved than a power-law , with a bolometric luminosity of ( 1.5 - 3 ) \times 10 ^ { 40 } erg s ^ { -1 } .
These results are interpreted as Comptonized emission from a black hole of 100 - 200 solar masses , radiating roughly at the Eddington luminosity .