IGR J18293-1213 is an eclipsing cataclysmic variable

Abstract

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, Δt = 30.8-0.0+6.3 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 Mwd = 0.78-0.09+0.10 M⊙. Assuming that the mass to radius ratio of the companion star M*/R* = 1 (solar units) and using T, Δt, and Mwd, 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 = (72.2-0.0+2.4) ± 1.0.