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

TL;DR

This paper reports the discovery of a probable gamma-ray pulsar binary with a 16.5-hour orbit, characterized by optical and spectroscopic data indicating a pulsar with a non-degenerate companion, likely a recycled millisecond pulsar.

Contribution

First identification of a gamma-ray source as a probable pulsar binary through combined optical and spectroscopic observations.

Findings

Binary with 16.5-hour period identified

Evidence for a non-degenerate secondary star

Source likely a recycled millisecond pulsar

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.