BERNARDINI, FedericoFedericoBERNARDINI0000-0001-5326-2010DE MARTINO, DomitillaDomitillaDE MARTINO0000-0002-5069-4202Mukai, K.K.MukaiFalanga, M.M.FalangaMASETTI, NICOLANICOLAMASETTI0000-0001-9487-77402020-12-282020-12-2820190035-8711http://hdl.handle.net/20.500.12386/29213The 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^{circ}≲ i ≲ 90^{circ} and the mass ratio 0.18< M_2/M_{ WD}< 0.40. A companion mass M<SUB>2</SUB>=0.2-0.25 M_{\odot } with a radius R<SUB>2</SUB>=0.24-0.26 R_{\odot } and spectral type ∼M4, at D=209^{+3}_{-2} pc, is derived. A lower limit to the white dwarf mass of ∼ 0.6 M_{\odot } is obtained from the X-ray spectrum. An upper limit to the magnetic colatitude, β ≲ 50^{circ}, and a shift in azimuth, ψ ∼ 14^{circ}, 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_{\odot } 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.STAMPAenArticle10.1093/mnras/stz19512-s2.0-85071762093000489292800081http://arxiv.org/abs/1907.05318v1https://iopscience.iop.org/article/10.3847/1538-4357/ab2fdf2019MNRAS.489.1044BFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering