The Megasecond Chandra X-Ray Visionary Project Observation of NGC 3115
  (II): properties of point sources
  We have carried out an in-depth study of low-mass X-ray binaries (LMXBs)
detected in the nearby lenticular galaxy NGC 3115, using the Megasecond Chandra
X-Ray Visionary Project observation (total exposure time 1.1 Ms). In total we
found 136 candidate LMXBs in the field and 49 in globular clusters (GCs) above
2\sigma\ detection, with 0.3--8 keV luminosity L_X ~10^36-10^39 erg/s. Other
than 13 transient candidates, the sources overall have less long-term
variability at higher luminosity, at least at L_X > 2x10^37 erg/s. In order to
identify the nature and spectral state of our sources, we compared their
collective spectral properties based on single-component models (a simple power
law or a multicolor disk) with the spectral evolution seen in representative
Galactic LMXBs. We found that in the L_X versus photon index \Gamma_PL and L_X
versus disk temperature kT_MCD plots, most of our sources fall on a narrow
track in which the spectral shape hardens with increasing luminosity below
L_X~7x10^37 erg/s but is relatively constant (\Gamma_PL~1.5 or kT_MCD~1.5 keV)
above this luminosity, similar to the spectral evolution of Galactic neutron
star (NS) LMXBs in the soft state in the Chandra bandpass. Therefore we
identified the track as the NS LMXB soft-state track and suggested sources with
L_X<7x10^37 erg/s as atolls in the soft state and those with L_X>7x10^37 erg/s
as Z sources. Ten other sources (five are transients) displayed significantly
softer spectra and are probably black hole X-ray binaries in the thermal state.
One of them (persistent) is in a metal-poor GC.
