Gamma-Ray Eclipses and Orbital Modulation Transitions in the Candidate Redback 4FGL J1702.7-5655
Abstract
Observations with the Fermi Large Area Telescope (LAT) of the gamma-ray source 4FGL J1702.7-5655, previously classified as a candidate millisecond pulsar, show highly significant modulation at a period of 0.2438033 days (~5.85 hr). Further examination of the folded light curve indicates the presence of narrow eclipses, suggesting that this is a redback binary system. An examination of the long-term properties of the modulation over 13 years of LAT observations indicates that the orbital modulation of the gamma rays changed from a simple eclipse before early 2013 to a broader, more easily detected quasi-sinusoidal modulation. In addition, the time of the eclipse shifts to ~0.05 later in phase. This change in the orbital modulation properties, however, is not accompanied by a significant overall change in gamma-ray flux or spectrum. The quasi-sinusoidal component peaks ~0.5 out of phase with the eclipse, which would indicate inferior conjunction of the compact object in the system. Swift X-ray Telescope observations reveal a possible X-ray counterpart within the LAT error ellipse. However, radio observations obtained with the Australia Telescope Compact Array do not detect a source in the region. 4FGL J1702.7-5655 appears to have changed its state in 2013, perhaps related to changes in the intrabinary shock in the system. We compare the properties of 4FGL J1702.7-5655 to those of other binary millisecond pulsars that have exhibited orbital modulation in gamma-rays.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2022
- DOI:
- 10.3847/1538-4357/ac6fe2
- arXiv:
- arXiv:2203.05652
- Bibcode:
- 2022ApJ...935....2C
- Keywords:
-
- Gamma-ray sources;
- Low-mass x-ray binary stars;
- Millisecond pulsars;
- Neutron stars;
- Eclipsing binary stars;
- 633;
- 939;
- 1062;
- 1108;
- 444;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Accepted for publication in the Astrophysical Journal