Disk-to-Corona State Transition and Extreme X-ray Variability in the Tidal Disruption Event AT2019teq

TL;DR

This study provides a detailed five-year X-ray analysis of TDE AT2019teq, revealing extreme variability, spectral state transitions, and a long-lived corona, with implications for black hole mass estimation and accretion physics.

Contribution

It presents the first detailed spectral and timing analysis of AT2019teq, highlighting its extreme variability, state transition, and a long-lived corona, advancing understanding of TDE accretion processes.

Findings

Detected sub-mHz quasi-periodic oscillations with high significance.

Observed spectral evolution from soft to hard state.

Estimated black hole mass lower than host galaxy scaling predicts.

Abstract

We present a five-year X-ray spectral and timing analysis of the optically selected Tidal Disruption Event (TDE) AT2019teq, which displays extreme variability, including order-of-magnitude changes in flux on minute-to-day timescales, and a rare late-time emergence of hard X-ray emission leading to the longest-lived corona in a known TDE. In one epoch, we detect sub-mHz quasi-periodic oscillations with significance tested via MCMC-based red-noise simulations (p $\leq 0.03$). AT2019teq exhibits a clear spectral evolution from a soft (blackbody-dominated) state to a hard (power-law-dominated) state, with a late-time radio brightening that may be associated with the state transition. We identify similarities between AT2019teq's evolution and X-ray binary soft-to-hard state transitions, albeit at higher luminosity and much faster timescales. We use the presence of both a disk-dominated and a corona-dominated state to apply multiple mass estimators from X-ray spectral and variability properties. These techniques are mutually consistent within $2\sigma$ and systematically yield a lower black hole mass ($\log(M_{BH}/M_{\odot}) = 5.67 \pm 0.09$) than inferred from host galaxy scaling ($\log(M_{BH}/M_{\odot})=6.14 \pm 0.19$).