Neutron Stars and Black Holes in the Small Magellanic Cloud: The NuSTAR SMC Legacy Project

We present initial results from a new NuSTAR Legacy Survey, the deepest hard X-ray (E>10 keV) study of the Small Magellanic Cloud (SMC). We have observed tens of X-ray sources in three fields along the main body of this nearby star-forming galaxy; these three fields were chosen for their stellar and accreting binary populations. Each field was observed 2-3 times, totalling approximately 200 ks of exposure time per field. Given the proximity of the SMC (~60 kpc), we are able to reach lower luminosity limits (Lx > ~10E34 erg/s) than is possible for other extragalactic X-ray binary (XRB) populations. We also have the advantage of low overall extinction by observing the SMC. Previous studies of the XRB population in the SMC with softer X-rays (E<10 keV) have revealed a large Be-XRB population dominated by accreting pulsars, and with a noticeable absence of confirmed black-hole XRBs. Studying the XRB population of the SMC with NuSTAR allows us to place constraints on the compact object type due to spectral differences between accreting black holes and neutron stars in the hard X-rays (E>10 keV). In particular, by comparing the X-ray colors and luminosities of SMC XRBs with those of Galactic XRBs of known compact object type, we are able to place constraints on the nature of the accretors in these systems. Combined with age estimates from published star formation history maps, we are able to place constraints on formation timescales for compact object populations.