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 d) 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 × 10³³ $\rm {erg}~\rm {s}^{-1}$. The quiescent corona of SZ Psc was observed ~5.67 d after the flare using Swift observatory, and also ~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 ± 11 MK, 2.13 ± 0.05 × 10⁵⁶ cm^-3, 0.66 ± 0.09 $\rm {Z}_{\odot }$, respectively. Using the hydrodynamic loop modelling, we derive the loop length of the flare as 6.3 ± 0.5 × 10¹¹ cm, whereas the loop pressure and density at the flare peak are derived to be 3.5 ± 0.7 × 10³ dyn cm^-2 and 8 ± 2 × 10¹⁰ cm^-3, respectively. The total magnetic field to produce the flare is estimated to be 490 ± 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 subgiant and the high orbital velocity.