An 85-s X-ray quasi-periodicity after a stellar tidal disruption by a candidate intermediate-mass black hole
Zhang, Wenjie; Shu, Xinwen; Sun, Luming; Shen, Rong-Feng; Dou, Liming; Jiang, Ning; Wang, Tinggui February 2025, Nature Astronomy, Advanced Online Publication
It is still in dispute whether intermediate-mass black holes (IMBHs) with a mass of ~103-105 solar masses (M⊙) exist, which are the missing link between stellar-mass black holes (5-50 M⊙) and supermassive black holes (106-1010 M⊙). The bright flares from tidal disruption events (TDEs) provide a new and direct way to probe IMBHs. 3XMM J215022.4-055108 is a unique off-nuclear X-ray transient that can be best explained as the TDE by an IMBH in a massive star cluster, although its mass is not well determined. Here we report the discovery of a transient X-ray quasi-periodicity signal from 3XMM J215022.4-055108 with a period of ~85 s (at a significance of >3.51σ) and fractional root-mean-squared amplitude of ~10%. Furthermore, the signal is coherent with a quality factor of ~16. The significance drops to >3.13σ if considering all light curves with sufficient quality for quasi-periodic oscillation search. Combined with the results from X-ray continuum fittings, the detection of quasi-periodic oscillation allows joint constraints on the black hole mass and dimensionless spin in the range of 9.9 × 103 to 1.6 × 104 M⊙ and 0.26 to 0.36, respectively. This result supports the presence of an IMBH in an off-nuclear massive star cluster and may allow the study of IMBHs through X-ray timing of TDEs.
