首颗OGLE发现的超致密X射线双星是一颗中介极星
The first OGLE-discovered ultracompact X-ray binary is an intermediate polar
AI总结：
本研究发现首颗OGLE发现的超致密X射线双星OGLE-UCXB-01符合中介极星模型，其光学和X射线变化源于磁化白矮星的吸积自转加快，排除了引力波驱动轨道衰减的假设。
摘要：
变源OGLE-UCXB-01是首颗由OGLE发现的超致密X射线双星（UCXB）。该源的12年长期OGLE光学测光显示其周期为P= 12.8 min，周期快速下降率为Pdot= -9.2E-11 s s^-1。在X射线光度L_X ~ 4E33 erg s^-1下，其X射线辐射也是变化的，并且与光学变化相关。为了确定该变源的本质，特别是其双星组件的质量和类型，我们首先考虑了一种有吸引力的可能性，即光学变化是由伴星的椭球变形引起的，且强烈的引力波辐射驱动了轨道衰减。然而，我们无法为伴星找到一个同时满足三个约束条件的允许解：超紧密轨道、高绝对星等和亮度变化的大振幅。此外，推断出的质量转移率过高。因此，排除了这一情景。随后，我们发现该系统与“中介极星”模型完全一致，在该模型中，光学和X射线辐射来自一颗从低质量（<~ 0.7 M_sun）主序伴星吸积的磁化白矮星（WD）。观测到的周期衰减是由吸积驱动的WD自转加快。WD自转周期为12.8 min，轨道周期短于10 hr。本文提出的方法可应用于仅有时间域数据可用的其他UCXB候选体或冒充体。
英文摘要：
The variable source OGLE-UCXB-01 is the first OGLE-discovered ultracompact X-ray binary (UCXB). The 12-year long-term OGLE optical photometry of this source shows a period of P= 12.8 min and a fast period decreasing rate Pdot= -9.2E-11 s s^-1. At a luminosity of L_X ~ 4E33 erg s^-1, its X-ray emission is also variable and correlated with the optical variability. To determine the nature of this variable source, specifically the masses and types of its binary components, we consider first an attractive possibility that the optical variation is due to the secondary's ellipsoidal variation and a strong gravitational wave emission drives the orbital decay. However, we can not find an allowable solution to the secondary that satisfies simultaneously the three constraints: an ultra-tight orbit, the bright absolute magnitude, and the large amplitude of the brightness variation. Moreover, the inferred mass transfer rate is too high. This scenario is therefore ruled out. We then find the system is fully consistent with an "intermediate polar" model, in which the optical and X-ray emission comes from a magnetized white dwarf (WD) accreting from a low-mass (<~ 0.7 M_sun) main-sequence secondary. The observed period decay is the accretion-driven spin-up of the WD. The WD spin period is 12.8 min and the orbital period is shorter than 10 hr. The method presented here can be applied to other UCXB candidates or impostors with time-domain data available only.
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