IGR J18293-1213 is an eclipsing cataclysmic variable

Studying the population of faint hard X-ray sources along the plane of the Galaxy is challenging because of high extinction and crowding, which make the identification of individual sources more difficult. IGR J18293-1213 is part of the population of persistent sources which have been discovered by the INTEGRAL satellite. We report on NuSTAR and Swift/XRT observations of this source, performed on 2015 September 11. We detected three eclipsing intervals in the NuSTAR light curve, allowing us to constrain the duration of these eclipses, Δ t= 30.8^{+6.3}_{-0.0} min, and the orbital period of the system, T = 6.92 ± 0.01 h. Even though we only report an upper limit on the amplitude of a putative spin modulation, the orbital period and the hard thermal bremsstrahlung spectrum of IGR J18293-1213 provide strong evidence that this source is a magnetic cataclysmic variable. Our NuSTAR and Swift/XRT joint spectral analysis places strong constraints on the white dwarf mass M_wd = 0.78^{+0.10}_{-0.09} M_⊙. Assuming that the mass to radius ratio of the companion star M_⋆/R_⋆ = 1 (solar units) and using T, Δt, and M_wd, we derived the mass of the companion star M_⋆ = 0.82 ± 0.01 M_⊙, the orbital separation of the binary system a = 2.14 ± 0.04 R_⊙, and its orbital inclination compared to the line of sight I=(72.2°^{+2.4}_{-0.0})± 1.0°.