Extragalactic X-ray binaries from 0.5-30 keV with Chandra and NuSTAR

An important ingredient in starburst galaxies is the population of black holes and neutron stars contained in accreting binary populations. We report on X-ray binary (XRB) populations in six nearby starburst galaxies using focused images over 0.5-30 keV with Chandra and NuSTAR. We use a set of hard X-ray color-color and color-count rate diagnostics developed using archival RXTE data, allowing identification of the much fainter extragalactic XRBs. We consistently find that the hard X-ray emission from these galaxies is dominated by XRBs (black holes and neutron stars) except in the well-known Compton-thick AGN candidate Arp 299. The detected XRBs appear dominated by intermediate-state black holes and the overall L_X is dominated by a handful of ULXs whose spectrum is overall well-described by a soft turnover. We discuss the cosmic implications of these results, including for the 7 Ms Chandra Deep Field survey, which will have just finished being observed at the time of the January 2015 AAS, and should include a significant population of X-ray emitting starburst galaxies like the ones discussed here.