2PBC J0658.0-1746: A hard X-ray eclipsing polar in the orbital period gap

F. Bernardini, D. De Martino, K. Mukai, M. Falanga, N. Masetti

    Research output: Contribution to journalArticlepeer-review


    The hard X-ray source 2PBC J0658.0-1746 was proposed as an eclipsing magnetic cataclysmic variable of the polar type, based on optical follow-ups. We present the first spectral and timing analysis at X-ray energies with XMM-Newton, complemented with archival X-ray, optical, infrared (IR) photometry, and spectroscopy. The X-ray emission shows bright and faint phases and total eclipses recurring every 2.38 h, consistent with optical properties. This firmly identifies 2PBC J0658.0-1746 as an eclipsing polar, the second hard X-ray selected in the orbital period gap. The X-ray orbital modulation changes from cycle-to-cycle and the X-ray flux is strongly variable over the years, implying a non-stationary mass accretion rate both on short and long time-scales. The X-ray eclipses allow to refine the orbital ephemeris with period 0.09913398(4) d, and to constrain the binary inclination 79 i 90 and the mass ratio 0.18< M2/MWD <0.40. A companion mass M2 = 0.2 − 0.25 M with a radius R2 = 0.24 − 0.26 R and spectral type ∼M4, at D= 209+32 pc, is derived. A lower limit to the white dwarf mass of ∼ 0.6 M is obtained from the X-ray spectrum. An upper limit to the magnetic colatitude, β 50, and a shift in azimuth, ψ ∼ 14, of the main accreting pole are also estimated. The optical/IR spectral energy distribution shows large excess in the mid-IR due to lower harmonics of cyclotron emission. A high-state mass accretion rate ∼ 0.4 − 1 × 10−10 M yr−1, lower than that of cataclysmic variables above the gap and close to that of systems below it, is estimated. With 2PBC J0658.0-1746, the number of hard X-ray-selected polars increases to 13 members, suggesting that they are not as rare as previously believed.

    Original languageEnglish (US)
    Pages (from-to)1044-1053
    Number of pages10
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number1
    StatePublished - Oct 11 2019


    • (2PBCJ0658.0-1746, 1RXS J065806.3-1744, 2MASS 06580591-1744249, WISE J065805.87-174424.5)
    • Cataclysmic variables - X-rays: individual: SWIFT J0658.0−1746
    • Novae

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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