A Compact X-Ray Emitting Binary in Likely Association with 4FGL J0935.3+0901

Abstract

4FGL J0935.3+0901 is a gamma-ray source detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope. We have conducted detailed analysis of the LAT data for this source and multi-wavelength studies of the source field. Its gamma-ray emission can be described with a power law ($\Gamma =2.0\pm 0.2$) with an exponential cutoff ($E_c=2.9\pm 1.6$ GeV), while the flux shows significant long-term variations. From analysis of archival Neil Gehrels Swift X-ray Telescope data, we find only one X-ray source in the LAT's 2$\sigma$ error region. Within a 3.7" radius error circle of the X-ray source, there is only one optical object down to $r^{\prime }\sim$23 mag. Time-resolved photometry of the optical object indicates a likely 2.5~hr periodic modulation, while its spectrum shows double-peaked hydrogen and helium emission lines (similar to those seen in accretion discs in low-mass X-ray binaries). Combining these results, we conclude that we have discovered a compact X-ray emitting binary in likely association with 4FGL J0935.3+0901, i.e., a millisecond pulsar (MSP) binary. We discuss the implication of the optical spectral features: this binary could be a transitional MSP system at a sub-luminous disc state, although the other possibility, the binary in a rotation-powered state showing the optical emission lines due to intrabinary interaction processes, can not be excluded. Further observational studies will help determine detailed properties of this candidate MSP binary and thus clarify its current state.

arXiv comment9 pages, 5 figures, 1 table, to appear in MNRAS

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Cited by in corpus (11)

• Incremental Fermi Large Area Telescope Fourth Source Catalog
• The Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars
• Transitional millisecond pulsars
• A New Flaring Black Widow Candidate and Demographics of Black Widow Millisecond Pulsars in the Galactic Field
• A New Candidate Transitional Millisecond Pulsar in the Sub-luminous Disk State: 4FGL J0407.7--5702
• Discovery of a New Redback Millisecond Pulsar Candidate: 4FGL J0940.3-7610
• Revealing a New Black Widow Binary 4FGL J0336.0+7502
• Optical Light Curve of 4FGL J0935.3+0901: A Flaring Black Widow Candidate
• Luminous Optical and X-ray Flaring of the Putative Redback Millisecond Pulsar 1FGL J0523.5$-$2529
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• Nature of 4FGL J2249.4+6229: Evidence for a redback system with a cool companion and low X-ray and $\gamma$-ray luminosities