Discovery of a variable multi-phase outflow in the X-ray-emitting tidal disruption event ASASSN-20qc

TL;DR

This paper reports the first detection of a multi-phase, variable outflow in the X-ray spectrum of the TDE ASASSN-20qc, revealing complex ionization and velocity structures in the outflowing material.

Contribution

It provides the first evidence of a multi-phase, variable outflow in a TDE, expanding understanding of outflow properties in such events.

Findings

Detection of multiple ionization phases with distinct velocities.

Observation of rapid ionization variability within a single observation.

Comparison of outflow characteristics with previous TDE ASASSN-14li.

Abstract

Tidal disruption events (TDEs) are exotic transients that can lead to temporary super-Eddington accretion onto a supermassive black hole. Such accretion mode is naturally expected to result in powerful outflows of ionized matter. However, to date such an outflow has only been directly detected in the X-ray band in a single TDE, ASASSN-14li. This outflow has a low velocity of just a few 100 km/s, although there is also evidence for a second, ultra-fast phase. Here we present the detection of a low-velocity outflow in a second TDE, ASASSN-20qc. The high-resolution X-ray spectrum reveals an array of narrow absorption lines, each blueshifted by a few 100 km/s, which cannot be described by a single photo-ionization phase. For the first time, we confirm the multiphase nature of a TDE outflow, with at least two phases and two distinct velocity components. One highly ionized phase is outflowing at $910^{+90}_{-80}$ km/s, while a lower ionization component is blueshifted by $400_{-120}^{+100}$ km/s. We perform time-resolved analysis of the X-ray spectrum and detect that, surprisingly, the mildly ionized absorber strongly varies in ionization parameter over the course of a single 60 ks observation, indicating that its distance from the black hole may be as low as 400 gravitational radii. We discuss these findings in the context of TDEs and compare this newly detected outflow with that of ASASSN-14li.