1FGL J1417.7-4407: A likely gamma-ray bright binary with a massive neutron star and a giant secondary

TL;DR

This paper reports the discovery of a gamma-ray bright binary system with a massive neutron star and a giant secondary, characterized by accretion disk features and high gamma-ray efficiency, representing a potential transitional state in binary evolution.

Contribution

It identifies and characterizes a new gamma-ray binary with a massive neutron star and a giant secondary, providing insights into its accretion and emission mechanisms.

Findings

Presence of an accretion disk indicated by variable H-alpha emission

High gamma-ray to X-ray luminosity ratio (~20) suggesting efficient gamma-ray production

System likely a low-mass X-ray binary not yet recycled into a pulsar

Abstract

We present multiwavelength observations of the persistent Fermi-LAT unidentified gamma-ray source 1FGL J1417.7-4407, showing it is likely to be associated with a newly discovered X-ray binary containing a massive neutron star (nearly 2 M_sun) and a ~ 0.35 M_sun giant secondary with a 5.4 day period. SOAR optical spectroscopy at a range of orbital phases reveals variable double-peaked H-alpha emission, consistent with the presence of an accretion disk. The lack of radio emission and evidence for a disk suggests the gamma-ray emission is unlikely to originate in a pulsar magnetosphere, but could instead be associated with a pulsar wind, relativistic jet, or could be due to synchrotron self-Compton at the disk--magnetosphere boundary. Assuming a wind or jet, the high ratio of gamma-ray to X-ray luminosity (~ 20) suggests efficient production of gamma-rays, perhaps due to the giant companion. The system appears to be a low-mass X-ray binary that has not yet completed the pulsar recycling process. This system is a good candidate to monitor for a future transition between accretion-powered and rotational-powered states, but in the context of a giant secondary.