Discovery of Two Polars from a Crossmatch of ZTF and the SRG/eFEDS X-ray Catalog

Abstract

Magnetic CVs are luminous Galactic X-ray sources but have been difficult to find in purely optical surveys due to their lack of outburst behavior. The eROSITA telescope aboard the Spektr-RG (SRG) mission is conducting an all-sky X-ray survey and recently released the public eROSITA Final Equatorial Depth Survey (eFEDS) catalog. We crossmatched the eFEDS catalog with photometry from the Zwicky Transient Facility (ZTF) and discovered two new magnetic cataclysmic variables (CVs). We obtained high-cadence optical photometry and phase-resolved spectroscopy for each magnetic CV candidate and found them both to be polars. Among the newly discovered magnetic CVs is ZTFJ0850+0443, an eclipsing polar with orbital period $P_{\text{orb}}=1.72$ hr, white dwarf mass $M_{\text{WD}}=0.81\pm 0.08M_{\odot }$ and accretion rate $\dot{M}\sim 10^{-11}{M}_{\odot }$/yr. We suggest that ZTFJ0850+0443 is a low magnetic field strength polar, with $B_{\text{WD}}\lesssim 10$ MG. We also discovered a non-eclipsing polar, ZTFJ0926+0105, with orbital period $P_{\text{orb}}=1.48$ hr, magnetic field strength $B_{\text{WD}}\gtrsim 26$ MG, and accretion rate $\dot{M}\sim 10^{-12}{M}_{\odot }$/yr.

Submitted to ApJ

References in corpus (31)

• The Zwicky Transient Facility: System Overview, Performance, and First Results
• 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 Zwicky Transient Facility: Science Objectives
• Second ROSAT all-sky survey (2RXS) source catalogue
• The SRG X-ray orbital observatory, its telescopes and first scientific results
• The Zwicky Transient Facility: Surveys and Scheduler
• The eROSITA Final Equatorial Depth Survey (eFEDS): The X-ray catalog
• Magnetic White Dwarfs
• A catalogue of white dwarfs in Gaia EDR3
• Physics Of Eclipsing Binaries. II. Towards the Increased Model Fidelity
• The Zwicky Transient Facility: Observing System
• First science with SALT: peering at the accreting polar caps of the eclipsing polar SDSS J015543.40+002807.2
• The origin and evolution of magnetic white dwarfs in close binary stars
• The eROSITA Final Equatorial-Depth Survey (eFEDS): Identification and characterization of the counterparts to the point-like sources
• Constraining the Evolution of Cataclysmic Variables via the Masses and Accretion Rates of their Underlying White Dwarfs
• Evidence for reduced magnetic braking in polars from binary population models
• X-Ray-Emitting Stars Identified from the ROSAT All-Sky Survey and the Sloan Digital Sky Survey
• Year 1 of the ZTF high-cadence Galactic Plane Survey: Strategy, goals, and early results on new single-mode hot subdwarf B-star pulsators
• Broad-band characteristics of seven new hard X-ray selected cataclysmic variables
• INTEGRAL view on Cataclysmic Variables and Symbiotic Binaries
• On accretion in the eclipsing polar BS Tri
• Cataclysmic Variables in the Second Year of the Zwicky Transient Facility
• Discovery of eRASSt J192932.9-560346: a bright, two-pole accreting, eclipsing polar
• 2PBC J0658.0-1746: a hard X-ray eclipsing polar in the orbital period gap
• Exploratory Spectroscopy of Magnetic Cataclysmic Variables Candidates and Other Variable Objects II
• MASTER OT J132104.04+560957.8: A Polar with Absorption-Emission Line Reversals
• The Magnetic Cataclysmic Variable LSQ1725-64
• Discovery, observations and modelling of a new eclipsing polar: MASTER OT J061451.70-272535.5
• Optical counterparts of ROSAT X-ray sources in two selected fields at low vs. high Galactic latitudes

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• Discovery and characterization of ZTF J0112+5827: An 80.9-minute polar with strong cyclotron features
• Cataclysmic Variable Candidates Identified in eROSITA-DE DR1,XMM-Newton, Swift, and ROSAT Catalogs
• A Study of Cataclysmic Variables from the eFEDS Survey
• Multiwavelength Characterization of a New Magnetic Cataclysmic Variable 2CXO J050740.7-091337