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

• Main Authors: Nabizadeh, Armin, Balman, Solen
• Format: Journal Article
• Language: English
• Published: 21-01-2020
• Subjects: Physics - High Energy Astrophysical Phenomena
• DOI: 10.48550/arxiv.2001.07486

We present the X-ray analysis of dwarf nova EY Cyg using the 45 ks
\textit{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 (\textit{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 \textit{XMM-Newton} EPIC spectra of the source yields a maximum
temperature $kT_{\rm max}$ $\sim$ 14.9$^{+3.3}_{-2.2}$ keV with an unabsorbed
X-ray flux and luminosity of (1.8--2.0) $\times$ 10$^{-12}$ ergs$^{-1}$
cm$^{-1}$ and (8.7--9.7) $\times$ 10$^{31}$ ergs$^{-1}$, respectively, in the
energy range 0.1 to 50 keV. There is 3--4 sigma excess at energies below 0.5
keV, we model the excess using \textit{MEKAL}, POWERLAW and BBODY models and
favor the model \textit{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 \textit{MEKAL} model
gives a temperature of $kT$ $\sim$ 0.1 keV with an unabsorbed X-ray flux and
luminosity of (2.7--8.8) $\times$ 10$^{-14}$ ergs$^{-1}$ cm$^{-1}$ and
(1.3--4.2) $\times$ 10$^{30}$ 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.