Nature of 4FGL J2249.4+6229: Evidence for a redback system with a cool companion and low X-ray and $\gamma$-ray luminosities

Abstract

We report the identification of the likely X-ray and optical counterpart to the unassociated Fermi source 4FGL J2249.4+6229. To clarify its nature, we investigate the X-ray data from Swift/XRT and SRG/eROSITA as well as photometric data from optical catalogues and archival spectroscopic data from the Gemini-North telescope. Using Zwicky Transient Facility data spanning over 6.6 yr, we confirmed a period of $\approx$5.6 h likely associated with the orbital motion in a binary system. The folded light curves have a smooth sinusoidal shape with two peaks per period and the amplitude of $\approx$0.2 mag. The X-ray spectra of the source are well fitted by an absorbed power law with the photon index of $\approx$2.0 and unabsorbed flux of $\approx$1.4$\times 10^{-13}$ erg s${}^{-1}$ cm${}^{-2}$. All these together with the X-ray to optical flux ratio of $\sim$0.2 implies that 4FGL J2249.4+6229 is a promising redback candidate. Fitting the optical light curves with the direct heating model, we obtained the companion mass of $\approx$0.5 M${}_{\odot }$ and temperature of $\approx$3600 K implying an M-type star. This places it among the coldest and most massive companions known in redback systems.Optical spectra confirms the M-type star and shows the broad asymmetric H$\alpha$ emission line. For the distance of 500--550 pc derived from the optical data, the source can be the redback with the lowest X-ray and $\gamma$-ray luminosities.

8 pages, 5 figures, accepted for publication in MNRAS

References in corpus (38)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• The eROSITA X-ray telescope on SRG
• The SRG X-ray orbital observatory, its telescopes and first scientific results
• The Zwicky Transient Facility Catalog of Periodic Variable Stars
• Optical spectroscopy and demographics of redback millisecond pulsar binaries
• A catalogue of cataclysmic variables from 20 years of the Sloan Digital Sky Survey with new classifications, periods, trends and oddities
• Einstein@Home Discovery of the Gamma-ray Millisecond Pulsar PSR J2039-5617 Confirms Its Predicted Redback Nature
• A real-time transient detector and the Living Swift-XRT Point Source catalogue
• A Spectroscopic Study of the Extreme Black Widow PSR J1311-3430
• A new gamma-ray loud, eclipsing low-mass X-ray binary
• Optical Counterparts of Two Fermi Millisecond Pulsars: PSR J1301+0833 and PSR J1628-3205
• The Synchrotron Emission Pattern of IntraBinary Shocks
• 1FGL J0523.5-2529: A New Probable Gamma-ray Pulsar Binary
• A New Flaring Black Widow Candidate and Demographics of Black Widow Millisecond Pulsars in the Galactic Field
• An Optical Study of the Black Widow Population
• A Likely Redback Millisecond Pulsar Counterpart of 3FGL J0838.8-2829
• A black widow population dissection through HiPERCAM multi-band light curve modelling
• A 62-minute orbital period black widow binary in a wide hierarchical triple
• Discovery of a New Redback Millisecond Pulsar Candidate: 4FGL J0940.3-7610
• PSR J1306--40: An X-ray Luminous Redback with an Evolved Companion
• Heated Poles on the Companion of Redback PSR J2339$-$0533
• Observational constraint from the heaviest pulsar PSR J0952-0607 on the equation of state of dense matter in relativistic mean field model
• The Intrabinary Shock and Companion Star of Redback Pulsar J2215+5135
• A Compact X-Ray Emitting Binary in Likely Association with 4FGL J0935.3+0901
• Revealing a New Black Widow Binary 4FGL J0336.0+7502
• A Multi-wavelength search for Black Widows and Redbacks counterparts of candidate $\gamma$-ray millisecond pulsars
• Optical Light Curve of 4FGL J0935.3+0901: A Flaring Black Widow Candidate
• A new redback pulsar candidate 4FGL J2054.2+6904
• Luminous Optical and X-ray Flaring of the Putative Redback Millisecond Pulsar 1FGL J0523.5$-$2529
• Evidence of intra-binary shock emission from the redback pulsar PSR J1048+2339
• Discovery of the variable optical counterpart of the redback pulsar PSR J2055+1545
• High Energy Emission from the Intrabinary Shocks in Redback Pulsars
• Nature of 4FGL J1838.2+3223: a flaring `spider' pulsar candidate
• 4FGL J1544.2$-$2554: a new spider pulsar candidate
• Optical Study of TRAPUM Pulsars and Modelling of the Redbacks: PSR J1036$-$4353 and PSR J1803$-$6707