Ultraviolet Spectral Evidence for Ansky as a Slowly Evolving Featureless Tidal Disruption Event with Quasiperiodic Eruptions
Jiazheng Zhu, Ning Jiang, Yibo Wang, Tinggui Wang, Luming Sun, Shiyan Zhong, Yuhan Yao, R. Chornock, Lixin Dai, Jianwei Lyu, Xinwen Shu, C. Fremling, Erica Hammerstein, Shifeng Huang, Wenkai Li, Bei You
Abstract
Abstract X-ray quasiperiodic eruptions (QPEs) are rare and enigmatic phenomena that increasingly show a connection to tidal disruption events (TDEs). However, the recently discovered QPEs in ZTF19acnskyy (“Ansky”) appear to be linked to an active galactic nucleus (AGN) rather than a TDE, as their slow decay and AGN-like variability differ markedly from that of typical TDEs. This finding may imply broader formation channels for QPEs. To further investigate Ansky’s nature, we obtained a timely ultraviolet (UV) spectrum, which reveals a featureless, TDE-like spectrum devoid of broad optical or UV emission lines. Additionally, the steep UV continuum, fitted by a power law with an index of −2.6, aligns more closely with TDEs than with AGNs. Compared to other featureless TDEs, Ansky exhibits a significantly lower blackbody luminosity (∼10 43 erg s −1 ) and much longer rise/decay timescales, suggesting a distinct TDE subclass. An offset TDE involving an intermediate-mass black hole is unlikely, given its position consistent with the galactic center, with a 3 σ upper limit of 54 pc. Instead, we propose that Ansky may result from the tidal disruption of a post-main-sequence star by a typical supermassive black hole. Our findings strengthen the growing evidence for TDE–QPE associations, although other formation channels for QPEs remain plausible and await future observational efforts.