RS CVn双星XY UMa初食附近的三个X射线耀斑
Three X-ray Flares Near Primary Eclipse of the RS CVn Binary XY UMa
摘要：
我们报告了对食RS CVn双星XY Uma（$\rm P_{orb}\approx$ 0.48 d）的存档X射线观测。在两个$\emph{Chandra}$ ACIS观测跨越200公里和几乎5个轨道周期，三个耀斑发生。我们在X射线通量中没有发现日食的证据。耀斑发生在主食前后，其中一次耀斑发生在主食后不久（$<0.125\rm P_{orb}$），另外两次耀斑发生在主食前不久（$<0.05\rm P_{orb}$）。两个耀斑发生在彼此大约一个轨道周期（$Δϕ\approx1.024\rm P_{orb}$）内。我们分析了系统的光变曲线和光谱，并研究了平静期和耀斑期间的日冕长度尺度，以及耀斑的时间。我们通过引入一个小的轨道偏心率来探索耀斑是轨道诱导的可能性，这对这颗近距离双星来说是相当具有挑战性的。
英文摘要：
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 ($Δϕ\approx1.024\rm P_{orb}$) 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.
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