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× 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 modeling, 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 dyne 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 sub-giant and the high orbital velocity.