A second radio flare from the tidal disruption event AT2020vwl: a delayed outflow ejection?

TL;DR

This paper reports the discovery of a second radio flare in TDE AT2020vwl, revealing evidence for multiple outflow ejections and providing insights into the mechanisms behind late-time radio flares in tidal disruption events.

Contribution

It presents the first detailed spectral analysis of multiple radio flares in a TDE, suggesting a delayed outflow ejection linked to peak accretion, which is a novel insight into TDE outflow mechanisms.

Findings

Second radio flare powered by a slower, more energetic outflow

Evidence for multiple outflow ejections or energy injections

Outflow velocity too low for off-axis relativistic jet explanation

Abstract

We present the discovery of a second radio flare from the tidal disruption event (TDE) AT2020vwl via long-term monitoring radio observations. Late-time radio flares from TDEs are being discovered more commonly, with many TDEs showing radio emission 1000s of days after the stellar disruption, but the mechanism that powers these late-time flares is uncertain. Here we present radio spectral observations of the first and second radio flares observed from the TDE AT2020vwl. Through detailed radio spectral monitoring, we find evidence for two distinct outflow ejection episodes, or a period of renewed energy injection into the pre-existing outflow. We deduce that the second radio flare is powered by an outflow that is initially slower than the first flare, but carries more energy and accelerates over time. Through modelling the long-term optical and UV emission from the TDE as arising from an accretion disc, we infer that the second radio outflow launch or energy injection episode occurred approximately at the time of peak accretion rate. The fast decay of the second flare precludes environmental changes as an explanation, while the velocity of the outflow is at all times too low to be explained by an off-axis relativistic jet. Future observations that search for any link between the accretion disc properties and late time radio flares from TDEs will aid in understanding what powers the radio outflows in TDEs, and confirm if multiple outflow ejections or energy injection episodes are common.