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تسجيل مستخدم جديدThe Effect of Variability on X-Ray Binary Luminosity Functions: Multiple Epoch Observations of NGC 300 with Chandra
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We have obtained three epochs of Chandra ACIS-I observations (totaling $sim$184 ks) of the nearby spiral galaxy NGC~300 to study the logN-logS distributions of its X-ray point source population down to $sim$2$times$10$^{-15}$ erg s$^{-1}$ cm$^{-2}$ in the 0.35-8 keV band (equivalent to $sim$10$^{36}$ erg s$^{-1}$). The individual epoch logN-logS distributions are best described as the sum of a background AGN component, a simple power law, and a broken power law, with the shape of the logN-logS distributions sometimes varying between observations. The simple power law and AGN components produce a good fit for persistent sources (i.e., with fluxes that remain constant within a factor of $sim$2). The differential power law index of $sim$1.2 and high fluxes suggest that the persistent sources intrinsic to NGC~300 are dominated by Roche lobe overflowing low mass X-ray binaries. The variable X-ray sources are described by a broken power law, with a faint-end power law index of $sim$1.7, a bright-end index of $sim$2.8-4.9, and a break flux of $sim$8$times10^{-15}$ erg s$^{-1}$ cm$^{-2}$ ($sim$4$times10^{36}$ erg s$^{-1}$), suggesting they are mostly outbursting, wind-fed high mass X-ray binaries, although the logN-logS distribution of variable sources likely also contains low-mass X-ray binaries. We generate model logN-logS distributions for synthetic X-ray binaries and constrain the distribution of maximum X-ray fluxes attained during outburst. Our observations suggest that the majority of outbursting X-ray binaries occur at sub-Eddington luminosities, where mass transfer likely occurs through direct wind accretion at $sim$1-3% of the Eddington rate.
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