We report the discovery of a new candidate ultraluminous X-ray source ( ULX ) in the nearby edge-on spiral galaxy NGC 891 .
The source , which has an absorbed flux of F _ { x } \sim 1 \times 10 ^ { -12 } erg s cm ^ { -2 } ( corresponding to a L _ { x } \gtrsim 10 ^ { 40 } erg s ^ { -1 } at 9 Mpc ) , must have begun its outburst in the past 5 years as it is not detected in prior X-ray observations between 1986 and 2006 .
We try empirical fits to the XMM-Newton spectrum , finding that the spectrum is fit very well as emission from a hot disk , a cool irradiated disk , or blurred reflection from the innermost region of the disk .
The simplest physically motivated model with an excellent fit is a hot disk around a stellar-mass black hole ( a super-Eddington outburst ) , but equally good fits are found for each model .
We suggest several follow-up experiments that could falsify these models .