Ultraviolet Spectral Evidence for Ansky as a Slowly Evolving Featureless Tidal Disruption Event with Quasiperiodic Eruptions

TL;DR

This study presents ultraviolet spectral evidence indicating that Ansky is a slowly evolving, featureless tidal disruption event with quasiperiodic eruptions, expanding understanding of TDE diversity and their connection to QPEs.

Contribution

The paper provides the first UV spectrum of Ansky, revealing TDE-like features and suggesting a new subclass of TDEs with longer timescales and lower luminosity, linked to post-main-sequence star disruptions.

Findings

Ansky's UV spectrum is featureless and TDE-like.

Ansky has a lower luminosity and longer timescales than typical TDEs.

Ansky's position is consistent with the galactic center, unlikely an offset TDE.

Abstract

X-ray quasi-periodic 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 and 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 sigma 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.