2010MNRAS.403L..69P

We present a theoretical study on the nature of the ultraluminous X-ray source NGC 1313 X-2. We evolved a set of binaries with high-mass donor stars orbiting a 20M_☉ or a 50-100M_☉black hole (BH). Using constraints from optical observations, we restricted the candidate binary system for NGC 1313 X-2 to be either a 50-100M_☉ BH accreting from a 12-15M_☉ main-sequence star or a ∼20M_☉ BH with a 12-15M_☉giant donor. If the modulation of 6.12±0.16 d recently identified as the orbital period of the system is confirmed, a ∼20M_☉ BH model becomes unlikely and we are left with the only possibility that the compact accretor in NGC 1313 X-2 is a massive BH of ∼50-100M_☉.