随机光学变异性与rms-通量关系在中间极EP240309a中的研究
Stochastic Optical Variability and an rms-flux Relation in the Intermediate Polar EP240309a
AI总结：
研究EP240309a的光学变异性，发现小时尺度上存在线性rms-通量关系，但存在时间依赖性，同时通过光谱分析得到特征半径约束，支持物质吸积至磁白矮星的模型。
摘要：
磁性爆发星为研究吸积与致密天体磁层相互作用及产生随机变异性提供了自然实验室。本文利用BOOTES光度计、高采样率TESS光变曲线和SOAR/Goodman光学光谱，对中间极候选星EP240309a进行了光学变异性研究。先前研究发现白矮星自转周期为3.97分钟（Pspin ~ 238秒）和轨道周期Porb = 3.7614(4)小时。BOOTES数据的功率谱密度一致于单幂律，斜率alpha ~ 1.2-1.8，无统计显著的转折证据。通过红噪声模拟和注入-恢复测试，对可能的转折频率置信区间，转换为磁层半径上限Rm <= 几x10^10厘米（MWD = 0.8 Msun）。在TESS数据中，三个高采样率区域检测到小时尺度上的线性rms-通量关系，而其他两个区域未发现稳健检测，表明时间依赖性rms-通量行为。SOAR光谱显示氢和氦II发射线，FWHM约1000-1600 km/s；根据开普勒解释，这些特征半径r约为(0.9-3.4)x10^10厘米，与基于时间的约束大致相当。总体而言，数据提供了保守的量级半径约束，支持吸积至磁白矮星的模型，但未确定详细的吸积几何或排除流体输运或混合吸积情景。
英文摘要：
Magnetic cataclysmic variables provide a natural laboratory for studying how accretion interacts with compact-object magnetospheres and generates stochastic variability. We present an optical variability study of the intermediate-polar candidate EP240309a, an Einstein Probe X-ray transient, using BOOTES photometry, high-cadence TESS light curves, and a SOAR/Goodman optical spectrum. Previous studies found a white-dwarf spin period of 3.97 min (Pspin ~ 238 s) and an orbital period of Porb = 3.7614(4) h. Power spectral densities from the BOOTES data are consistent with single power laws with slopes alpha ~ 1.2-1.8, with no statistically significant evidence for a bend across the sampled frequency range. Using red-noise simulations and injection-recovery tests, we place one-sided constraints on any putative break frequency, which translate, under standard dynamical identifications, into an upper limit on the magnetospheric radius of Rm <= few x 10^10 cm for MWD = 0.8 Msun. In the TESS data, we detect a linear rms-flux relation on hour timescales in three high-cadence sectors, while two other sectors do not show a robust detection, indicating epoch-dependent rms-flux behavior. The SOAR spectrum shows Balmer and He II emission lines with FWHM about 1000-1600 km s^-1; under a Keplerian interpretation, these imply characteristic radii of r about (0.9-3.4) x 10^10 cm, broadly comparable to the timing-based constraints. Overall, the data provide conservative, order-of-magnitude radius constraints consistent with accretion onto a magnetic white dwarf, but they do not establish the detailed accretion geometry or exclude stream-fed or mixed accretion scenarios.
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