Swift and XMM-Newton observations of an RS CVn type eclipsing binary SZ Psc: Superflare and coronal properties

Abstract

We present an in-depth study of a large and long duration ($>$1.3 days) X-ray flare observed on an RS CVn type eclipsing binary system SZ Psc using observations from Swift observatory. In the 0.35$-$10 keV energy band, the peak luminosity is estimated to be 4.2$\times$10$^{33}$ erg s$^{-1}$. The quiescent corona of SZ Psc was observed $\sim$5.67 d after the flare using Swift observatory, and also $\sim$1.4 yr after the flare using the XMM-Newton satellite. The quiescent corona is found to consist of three temperature plasma: 4, 13, and 48 MK. High-resolution X-ray spectral analysis of the quiescent corona of SZ Psc suggests that the high first ionization potential (FIP) elements are more abundant than the low-FIP elements. The time-resolved X-ray spectroscopy of the flare shows a significant variation in the flare temperature, emission measure, and abundance. The peak values of temperature, emission measure, and abundances during the flare are estimated to be 199$\pm$11 MK, 2.13$\pm$0.05 $\times 10^{56}$ cm$^{-3}$, 0.66$\pm$0.09 Z$_{\odot}$, respectively. Using the hydrodynamic loop modeling, we derive the loop length of the flare as 6.3$\pm$0.5 $\times 10^{11}$ cm, whereas the loop pressure and density at the flare peak are derived to be 3.5$\pm$0.7 $\times 10^{3}$ dyne cm$^{-2}$ and 8$\pm$2 $\times 10^{10}$ cm$^{-3}$, respectively. The total magnetic field to produce the flare is estimated to be 490$\pm$60 G. The large magnetic field at the coronal height is supposed to be due to the presence of an extended convection zone of the sub-giant and the high orbital velocity.