A period distribution of X-ray binaries observed in the central region of M31 with Chandra and HST

摘要: Almost all Galactic black hole binaries with low mass donor stars are transient X-ray sources; we expect most of the transients observed in external galaxies to be also. Obtaining period estimates for extra-galactic is challenging, but resulting distribution an important tool modeling evolution history host galaxy. We have obtained periods, or upper limits, 12 M31, using updated relation between optical and luminosities. monitored central region M31 Chandra last ~12 years, followed up promising HST; 4\sigma B magnitude limits counterparts ~26--29, depending on crowding. obtain each both neutron star accretors. Periods range from <0.4 490+/-90 hours (<0.97 <175 hrs if BH systems). These appear somewhat skewed towards shorter periods than Milky Way (MW) transients; indeed, comparing MW survival analysis techniques used account some data only yield probabilities ~0.02--0.08 that two populations drawn same distribution. also checked a correlation orbital distance nucleus, finding 12% probability no correlation. Further observations will strengthen these results.