X-Ray binary population in M31

We fit the spectral energy distributions of optical counterpart candidates using the Bayesian Extinction and Stellar Tool. We used the best-fit luminosity, effective temperature, radius, and dust reddening for the companion stars in combination with the local star formation history, dust maps of M31, published X-ray spectral fits from XMM-Newton observations, IR colors, and Chandra X-ray hardness ratios to determine our best sample of HMXB candidates.

The age distribution of the HMXB sample appears peaked between 10 and 50Myr, consistent with findings in other nearby galaxies. Using the age distribution and mean star formation rate (SFR), we find that 80-136HMXBs were produced per unit of SFR over the last 50Myr and 89-163HMXBs were produced per unit of SFR over the last 80Myr, if we expand the assumed age limit beyond the lifetimes of single massive stars. We also calculate the HMXB production rate (HMXBs/M{sun}) over time, which ranges from 7x10^-7^ to 4x10^-6^HMXBs/M{sun} over the last 80Myr, in agreement with both theoretical predictions and measured production rates in other galaxies.