Three X-ray Flares Near Primary Eclipse of the RS CVn Binary XY UMa

TL;DR

This study analyzes X-ray observations of the RS CVn binary XY UMa, revealing three flares near primary eclipse, examining their timing, spectra, and coronal structures, and exploring the potential influence of orbital eccentricity.

Contribution

It provides the first detailed analysis of X-ray flares near eclipse in XY UMa and investigates the possibility of orbit-induced flaring in a close binary system.

Findings

Three X-ray flares occurred near primary eclipse.

No evidence of X-ray eclipses was found.

Flares happened shortly before or after primary eclipse.

Abstract

We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa ($\rm P_{orb}\approx$ 0.48d). In two $\emph{Chandra}$ ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no evidence for eclipses in the X-ray flux. The flares took place around times of primary eclipse, with one flare occurring shortly ($<0.125\rm P_{orb}$) after a primary eclipse, and the other two happening shortly ($<0.05\rm P_{orb}$) before a primary eclipse. Two flares occurred within roughly one orbital period ($\Delta \phi\approx1.024\rm P_{orb}$) of each other. We analyze the light curve and spectra of the system, and investigate coronal length scales both during quiescence and during flares, as well as the timing of the flares. We explore the possibility that the flares are orbit-induced by introducing a small orbital eccentricity, which is quite challenging for this close binary.