The formation of ultraluminous X-ray sources with neutron star accretors

The recent discovery of a neutron star accretor in the ultra-luminous X-ray (ULX) source M82 X-2 challenges our understanding of high-mass X-ray binary formation and evolution. By combining binary population synthesis and detailed mass-transfer models, however, we show that the binary parameters of M82 X-2 are not surprising provided non-conservative mass transfer is allowed. Specifically, the donor-mass lower limit and orbital period measured for M82 X-2 lie near the most probable values predicted by population synthesis models, and systems such as M82 X-2 exist in approximately 13% of the galaxies with star formation history similar to M82. This work is presented in detail in Fragos et al.