1FGL J0523.5-2529: A New Probable Gamma-ray Pulsar Binary
  We report optical photometric and SOAR spectroscopic observations of an X-ray source found within the localization error of the Fermi-LAT unidentified gamma-ray source J0523.5-2529. The optical data show periodic flux modulation and radial velocity variations indicative of a binary with a 16.5-hr period. The data suggest a massive non-degenerate secondary (~> 0.8 M_sun), and we argue the source is likely a pulsar binary. The radial velocities have good phase coverage and show evidence for a measurable eccentricity (e=0.04). There is no clear sign of irradiation of the secondary in either photometry or spectroscopy. The spatial location out of the Galactic plane and gamma-ray luminosity of the source are more consistent with classification as a recycled millisecond pulsar than as a young pulsar. Future radio timing observations can confirm the identity of the primary and further characterize this interesting system. 
Jay Strader (Michigan St.), Laura Chomiuk (Michigan St.), Eda Sonbas   (Adiyaman), Kirill Sokolovsky (Lebedev/Sternberg), Da...
astro-ph.HE astro-ph.GA astro-ph.SR