A NuSTAR Census of the X-ray Binary Population of the M31 Disk

Abstract

Using hard (E>10 keV) X-ray observations with NuSTAR, we are able to differentiate between accretion states, and thus compact object types, of neutron stars and black holes in X-ray binaries (XRBs) in M31, our nearest Milky Way-type neighbor. Using ten moderate-depth (20-50 ks) observations of the disk of M31 covering a total of ~0.45 deg${}^2$, we detect 20 sources at 2$\sigma$ in the 4-25 keV band pass, 14 of which we consider to be XRB candidates. This complements an existing deeper (100-400 ks) survey covering ~0.2 deg${}^2$ of the bulge and the northeastern disk. We make tentative classifications of 9 of these sources with the use of diagnostic color-intensity and color-color diagrams, which separate sources into various neutron star and black hole regimes, identifying 3 black holes and 6 neutron stars. In addition, we create X-ray luminosity functions for both the full (4-25 keV) and hard (12-25 keV) band, as well as sub-populations of the full band based on compact object type and association with globular clusters. Our best fit globular cluster XLF is shallower than the field XLF, and preliminary BH and NS XLFs suggest a difference in shape based on compact object type. We find that the cumulative disk XLFs in the full and hard band are best fit by power laws with indices of 1.32 and 1.28 respectively. This is consistent with models of the Milky Way XLF from Grimm et al. (2002), Voss & Ajello (2010), and Doroshenko et al. (2014).

19 pages, 6 Figures, Published in ApJ

References in corpus (18)

• Array Programming with NumPy
• The NumPy array: a structure for efficient numerical computation
• X-ray Properties of Black-Hole Binaries
• HI4PI: A full-sky HI survey based on EBHIS and GASS
• The GALEX Ultraviolet Atlas of Nearby Galaxies
• NuSTAR Observations of the Bullet Cluster: Constraints on Inverse Compton Emission
• The Panchromatic Hubble Andromeda Treasury XI: The Spatially-Resolved Recent Star Formation History of M31
• X-ray Binary Luminosity Function Scaling Relations for Local Galaxies Based on Subgalactic Modeling
• The Metallicity Dependence of the High-Mass X-ray Binary Luminosity Function
• Spatially Resolving a Starburst Galaxy at Hard X-ray Energies: NuSTAR, Chandra, AND VLBA Observations of NGC 253
• Low-mass X-ray binaries in the bulge of the Milky Way
• X-ray Binary Luminosity Function Scaling Relations in Elliptical Galaxies: Evidence for Globular Cluster Seeding of Low-Mass X-ray Binaries in Galactic Fields
• X-ray luminosity function of high-mass X-ray binaries: Studying the signatures of different physical processes using detailed binary evolution calculations
• X-Rays Beware: The Deepest Chandra Catalogue of Point Sources in M31
• Neutron Stars and Black Holes in the Small Magellanic Cloud: The SMC NuSTAR Legacy Survey
• An X-ray spectral survey of the disc of M31 with XMM-Newton
• Population of the Galactic X-ray binaries and eRosita
• Multiwavelength Characterization of the High Mass X-ray Binary Population of M33