Revealing a New Black Widow Binary 4FGL J0336.0+7502

TL;DR

This paper reports the discovery of a new black widow millisecond pulsar binary candidate, 4FGL J0336.0+7502, identified through multi-wavelength observations, with properties consistent with known black widow systems and potential orbital X-ray modulation.

Contribution

The study presents the first identification of a black widow pulsar candidate with multi-wavelength evidence, including optical, X-ray, and gamma-ray data, suggesting a new member of this rare class.

Findings

Optical periodicity at 3.718178 hours confirmed.

X-ray source consistent with black widow properties.

Potential orbital X-ray modulation observed.

Abstract

We report on a discovery of a promising candidate as a black widow millisecond pulsar binary, 4FGL J0336.0+7502, which shows many pulsar-like properties in the 4FGL-DR2 catalog. Within the 95% error region of the LAT source, we identified an optical counterpart with a clear periodicity at P(orb) = 3.718178(9) hours using the Bohyunsan 1.8-m Telescope, Lulin One-meter Telescope, Canada-France-Hawaii Telescope, and Gemini-North. At the optical position, an X-ray source was marginally detected in the Swift/XRT archival data, and the detection was confirmed by our Chandra/ACIS DDT observation. The spectrum of the X-ray source can be described by a power-law model of Gamma = 1.6+/-0.7 and F(0.3-7keV) = 3.5e-14 erg/cm^2/s. The X-ray photon index and the low X-ray-to-gamma-ray flux ratio (i.e., < 1%) are both consistent with that of many known black widow pulsars. There is also a hint of an X-ray orbital modulation in the Chandra data, although the significance is very low (1.3 sigma). If the pulsar identity and the X-ray modulation are confirmed, it would be the fifth black widow millisecond pulsar binary that showed an orbitally-modulated emission in X-rays.