X-ray properties of dwarf nova EY Cyg and the companion star using an XMM-Newton observation

Abstract

We present the X-ray analysis of dwarf nova EY Cyg using the 45 ks XMM-Newton observatory archival data obtained in quiescence. We find orbital modulations in X-rays. We simultaneously fitted EPIC pn, MOS1 and MOS2 data using a model for interstellar medium absorption (tbabs) and a multi-temperature plasma emission model with a power-law distribution of temperatures (CEVMKL) as expected from low accretion rate quiescent dwarf novae. The XMM-Newton EPIC spectra of the source yields a maximum temperature kTmax∼14.9-2.2+3.3 keV with an unabsorbed X-ray flux and luminosity of (1.8–2.0) ×10-12 ergs−1 cm−1 and (8.7–9.7) ×1031 ergs−1, respectively, in the energy range 0.1–50 keV. There is 3–4 sigma excess at energies below 0.5 keV, we model the excess using MEKAL, POWERLAW and BBODY models and favor the model MEKAL which is physical. According to previous studies, the secondary in this system is thought to be a K-type star which may radiate in the soft X-ray region. The fit with an additive MEKAL model gives a temperature of kT ∼ 0.1 keV with an unabsorbed X-ray flux and luminosity of (2.7–8.8) ×10-14 ergs−1 cm−1 and (1.3–4.2) ×1030 ergs−1, respectively, for the companion star. Based on the results from the timing and spectral analysis, we highly suggest that the secondary of EY Cyg is a K-type star.