We have examined the optical/X-ray light curves of seven well-observed recurrent novae, V745 Sco, M31N 2008-12a, LMC N 1968, U Sco, RS Oph, LMC N 2009a, T Pyx, and one recurrent nova candidate LMC N 2012a. Six novae out of the eight show a simple relation that the duration of supersoft X-ray source (SSS) phase is 0.70 times the total duration of the outburst ($=$ X-ray turnoff time), i.e., $t_{\rm SSS}=0.70 t_{\rm off}$, the total duration of which ranges from 10 days to 260 days. These six recurrent novae show a broad rectangular X-ray light curve shape, first half a period of which is highly variable in the X-ray count rate. The SSS phase corresponds also to an optical plateau phase that indicates a large accretion disk irradiated by a hydrogen-burning WD. The other two recurrent novae, T Pyx and V745 Sco, show a narrow triangular shape of X-ray light curve without an optical plateau phase. Their relations between $t_{\rm SSS}$ and $t_{\rm off}$ are rather different from the above six recurrent novae. We also present theoretical SSS durations for recurrent novae with various WD masses and stellar metallicities ($Z=$0.004, 0.01, 0.02, and 0.05) and compare with observed durations of these recurrent novae. We show that the SSS duration is a good indicator of the WD mass in the recurrent novae with a broad rectangular X-ray light curve shape.

中文翻译：

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复发新星的超软 X 射线相位作为其白矮星质量的指标

我们检查了 7 颗观测良好的复发新星、V745 Sco、M31N 2008-12a、LMC N 1968、U Sco、RS Oph、LMC N 2009a、T Pyx 和一颗复发新星候选 LMC 的光学/X 射线光变曲线N 2012a。八颗新星中的六颗显示出一个简单的关系，即超软 X 射线源 (SSS) 阶段的持续时间是爆发总持续时间（$=$ X 射线关闭时间）的 0.70 倍，即 $t_{\rm SSS}=0.70 t_{\rm off}$，其总持续时间从 10 天到 260 天不等。这六颗复发新星呈现出宽阔的矩形 X 射线光变曲线形状，其前半个周期的 X 射线计数率变化很大。SSS 阶段也对应于一个光学平台阶段，表明一个大的吸积盘被氢燃烧的 WD 照射。另外两个反复出现的新星，T Pyx 和 V745 Sco，显示没有光学平台相位的窄三角形 X 射线光曲线。它们之间的 $t_{\rm SSS}$ 和 $t_{\rm off}$ 之间的关系与上述六颗复发新星有很大不同。我们还介绍了具有各种 WD 质量和恒星金属丰度（$Z=$0.004、0.01、0.02 和 0.05）的复发新星的理论 SSS 持续时间，并与这些复发新星的观测持续时间进行了比较。我们表明，SSS 持续时间是具有宽矩形 X 射线光曲线形状的复发新星中 WD 质量的良好指标。05) 并与这些反复出现的新星的观测持续时间进行比较。我们表明，SSS 持续时间是具有宽矩形 X 射线光曲线形状的复发新星中 WD 质量的良好指标。05) 并与这些反复出现的新星的观测持续时间进行比较。我们表明，SSS 持续时间是具有宽矩形 X 射线光曲线形状的复发新星中 WD 质量的良好指标。