Confirmation of two magnetic cataclysmic variables as polars: 1RXS J174320.1−042953 and YY Sex

Abstract

We present our analysis of new and archived observations of two candidate magnetic cataclysmic variables, namely 1RXS J174320.1−042953 and YY Sex. 1RXS J174320.1−042953 was observed in two distinctive high and low states where a phase shift was seen, which could be due to changes in the shape, size, and (or) location of the accretion region. We find that its orbital X-ray modulations only persist in the soft (0.3–2.0 keV) energy band, which could be attributed to photoelectric absorption in the accretion flow. The X-ray spectra exhibit a multi-temperature post-shock region where the hard X-rays are absorbed through a thick absorber with an equivalent hydrogen column of ∼7.5 × 1023 cm−2, which partially covers ∼56 per cent of the emission. No soft X-ray excess was found to be present; however, a soft X-ray emission with a blackbody temperature of ∼97 eV describes the spectra. Extensive Transiting Exoplanet Survey Satellite (TESS) observations of YY Sex allow us to refine its orbital period to 1.5746 ± 0.0011 h. We did not find any signature of previously reported spin or beat periods in this system. Furthermore, our new polarimetric observations show clear circular polarization modulated on the orbital period only. Finally, both systems show strong Balmer and He II 4686 Å emission lines in the optical spectra, further indicative of their magnetic nature.