eROSITA全天巡天——恒星与光学负载
eROSITA all-sky survey - stars and optical loading
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中文总结 AI 辅助
本研究针对eROSITA全天巡天（eRASS），分析恒星受光学负载的影响，明确其相关性与标记规则，为解释恒星eRASS数据提供热等离子体模型的硬度比及计数率转换方法。
中文摘要 AI 辅助
Spectrum-Roentgen-Gamma（SRG）航天器搭载的eROSITA（带成像望远镜阵列的扩展X射线巡天）已完成X射线波段的eROSITA全天巡天（eRASS）。本研究针对较亮恒星，评估eROSITA全天巡天（此处特指eRASS:3）中光学负载的影响；同时利用热等离子体模型研究恒星eRASS源的一般性质，并将受光学负载影响的恒星与日冕源进行对比。我们将盖亚（Gaia）DR3、第谷-2（Tycho-2）、2MASS及SIMBAD数据库的数据，与较亮恒星的eRASS计数率进行比对；对疑似受光学负载影响的源，分析其X射线图像、光变曲线和光谱，确定其性质。我们将eROSITA源的性质与生成的一套APEC模型光谱的真实日冕源进行比对，确定恒星X射线发射体的计数率转换因子和硬度比。关于光学负载，我们发现光学亮度与观测到的最小计数率在约2至5等（V/G波段）范围内存在明确相关性，极亮源的该关系会饱和；星等和颜色是主要决定因素，曝光深度和特定扫描路径也有影响。对于本征X射线发射体，同样会观测到光学污染。我们对虚假X射线源进行特征刻画，解决伪变异性和光谱性质问题，提供热等离子体模型的硬度比和计数率转换以解释恒星eRASS数据。研究详细分析了易受光学负载影响的eROSITA数据，DR2的光学负载标记设置规则为：源亮于5.0等（B、V、G）或3.5等（J），该规则与曝光深度略有相关，预计未来数据发布仅会有微小变动。
英文摘要
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) on board the Spectrum-Roentgen-Gamma (SRG) spacecraft has performed the eROSITA All-Sky Survey (eRASS) at X-ray energies. We study the brighter stars to assess the impact of optical loading in the eROSITA all-sky survey, here specifically the eRASS:3. Further we use thermal plasma models to investigate the general properties of stellar eRASS sources and compare optical loading affected stars to coronal sources. We compare data from Gaia DR3, Tycho-2, 2MASS and the SIMBAD database with the eRASS count rates of brighter stars. We analyze X-ray images, light curves and spectra for sources suspected to be affected by optical loading and determine their properties. eROSITA source properties are checked in comparison to genuine coronal sources with generated sets of APEC model spectra, where we determine rate conversion factors and hardness ratios for stellar X-ray emitter. Regarding optical loading we find a clear correlation between optical brightness and observed minimum count rate in the range of about 2\,--\,5 mag (V/G band), which then saturates for very bright sources. While magnitude and color are the main determinants, exposure depth and specific scanning paths also matter. For intrinsic X-ray emitters, optical contamination is likewise observed. We characterize the fake X-ray sources, address pseudo variability and spectral properties. To interpret stellar eRASS data, hardness ratios and count rate conversions for thermal plasma models are provided. The eROSITA data is prone to optical loading, which was studied in greater detail. The optical loading flag for the DR2 is set, if sources are brighter than 5.0~mag (B, V, G) or 3.5~mag (J). It is somewhat dependent on exposure depth, but we expect only minor changes for future data releases.
