标题： eRASSt J074426.3+291606：'暗淡且缓慢'潮汐撕裂事件中快速吸积盘形成 显示英文标题

标题： eRASSt J074426.3+291606: prompt accretion disc formation in a 'faint and slow' tidal disruption event

摘要： 我们报告对潮汐破坏事件(TDE)候选体eRASSt J074426.3+291606 (J0744)的多波长观测，该天体位于一个之前处于休眠状态的星系核心，距离为$z=0.0396$。 J0744首次在第二轮SRG/eROSITA全天空调查(eRASS2)中被发现为一个新的超软X射线源（光子指数$\sim 4$），在此期间，它在0.3--2~keV波段的亮度比2011年一次偶然的钱德拉探测得出的档案3$\sigma$上限提高了超过$\sim$160倍。 该暂现源也在光学波段由兹维基瞬变工厂(ZTF)独立发现，eRASS2的探测发生在光学亮度峰值仅$\sim$20天后，这表明在这个TDE中吸积盘迅速形成。 在接下来的$\sim$400 天里，通过 eROSITA、NICER XTI 和 Swift XRT 进行的持续 X 射线监测显示，其净下降幅度为$\sim$100 倍，尽管存在较大的 X 射线变化，系统在 0.3--2~keV 波段内会变暗，然后重新变亮，在 80 天期间变化幅度为$\sim$50 倍。 在此极端 X 射线变化期间的同时 Swift UVOT 观测结果显示，相对平滑的下降持续了$\sim$400 天之后的光学峰值。 来自这一暂现源的峰值观测光学光度（绝对$g$-波段星等$\sim -16.8$mag）使 J0744 成为至今观测到的最暗的光学探测到的 TDE。 然而，与已知的“暗且快”TDEs 相比，J0744 的光学辐射衰减较慢（指数衰减时间尺度$\sim$120~天），使 J0744 成为潜在的新一类“暗且慢”TDEs 的首个成员。 显示英文摘要

摘要： We report on multi-wavelength observations of the tidal disruption event (TDE) candidate eRASSt J074426.3+291606 (J0744), located in the nucleus of a previously quiescent galaxy at $z=0.0396$. J0744 was first detected as a new, ultra-soft X-ray source (photon index $\sim 4$) during the second SRG/eROSITA All-Sky Survey (eRASS2), where it had brightened in the 0.3--2~keV band by a factor of more than $\sim$160 relative to an archival 3$\sigma$ upper limit inferred from a serendipitous Chandra pointing in 2011. The transient was also independently found in the optical by the Zwicky Transient Factory (ZTF), with the eRASS2 detection occurring only $\sim$20 days after the peak optical brightness, suggesting that the accretion disc formed promptly in this TDE. Continued X-ray monitoring over the following $\sim$400 days by eROSITA, NICER XTI and Swift XRT showed a net decline by a factor of $\sim$100, albeit with large amplitude X-ray variability where the system fades, and then rebrightens, in the 0.3--2~keV band by a factor $\sim$50 during an 80 day period. Contemporaneous Swift UVOT observations during this extreme X-ray variability reveal a relatively smooth decline, which persists over $\sim$400 days post-optical peak. The peak observed optical luminosity (absolute $g$-band magnitude $\sim -16.8$ mag) from this transient makes J0744 the faintest optically-detected TDE observed to date. However, contrasting the known set of `faint and fast' TDEs, the optical emission from J0744 decays slowly (exponential decay timescale $\sim$120~days), making J0744 the first member of a potential new class of `faint and slow' TDEs.