Optical Light Curve of 4FGL J0935.3+0901: A Flaring Black Widow Candidate

Abstract

I obtained time-series photometry of the compact binary candidate for the Fermi source 4FGL J0935.3+0901. Superposed on the 2.44 hr orbital modulation are day-to-day variations and frequent flaring as seen in several redback and black widow millisecond pulsars (MSPs). The short orbital period favors a black widow. While the modulation of $\le 1$ mag is smaller than that of most black widows, it could indicate a low orbital inclination. Although a published optical spectrum shows strong emission lines, the light curve evinces pulsar heating of the companion star rather than accretion-disk emission of a transitional MSP. Emission lines and flaring occur in the same objects, probably powered by shocks between the relativistic pulsar wind and a wind driven off the companion star. I also recovered the period in photometry from the Zwicky Transient Facility. A phase-connected ephemeris derived from MDM Observatory and ZTF data spanning 4 years yields a period of 0.10153276(36) days and an epoch for the ascending node of the putative pulsar.

8 pages, 3 figures, corrected references, published in ApJ Letters

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• A New Flaring Black Widow Candidate and Demographics of Black Widow Millisecond Pulsars in the Galactic Field
• Luminous Optical and X-ray Flaring of the Putative Redback Millisecond Pulsar 1FGL J0523.5$-$2529
• The black widow pulsar J1641+8049 in the optical, radio and X-rays
• Two black widow pulsars in the optical and X-rays
• Nature of 4FGL J1838.2+3223: a flaring `spider' pulsar candidate
• 4FGL J1544.2$-$2554: a new spider pulsar candidate
• Nature of 4FGL J2249.4+6229: Evidence for a redback system with a cool companion and low X-ray and $\gamma$-ray luminosities