1FGL J0523.5-2529: A New Probable Gamma-ray Pulsar Binary

Abstract

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.

ApJ Letters in press (v2: very small changes to match published version)

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• 2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable $\gamma$-ray emission
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• PSR J1306--40: An X-ray Luminous Redback with an Evolved Companion
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• Fermi Variability Study of the Candidate Pulsar Binary 2FGL~J0523.3-2530
• Periodicity search for Pulsar Binaries with TESS
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