Lightcurve Evolution of the nearest Tidal Disruption Event: A late-time, radio-only flare

TL;DR

This paper presents late-time radio observations of a TDE in NGC 4845, revealing a radio flare caused by jet-cloud interaction, and reanalyzes X-ray data to confirm the TDE nature of the event.

Contribution

It provides the first detailed radio lightcurve showing a late-time flare in a TDE and models the flare as jet-cloud interaction, offering new insights into TDE radio evolution.

Findings

Radio flux decayed until 2015, then plateaued and flared in 2016.

Radio flare was not accompanied by X-ray changes.

Reanalysis confirms thermal disk emission and extreme X-ray flux increase.

Abstract

Tidal disruption events (TDEs) occur when a star passes close enough to a galaxy's supermassive black hole to be disrupted by tidal forces. We discuss new observations of IGRJ12580+0134, a TDE observed in NGC 4845 (d=17 Mpc) in November 2010, with the Karl G. Jansky Very Large Array (JVLA). We also discuss a reanalysis of 2010-2011 Swift and XMM-Newton observations, as well as new, late-time Swift observations. Our JVLA observations show a decay of the nuclear radio flux until 2015, when a plateau was seen, and then a significant (~factor 3) radio flare during 2016. The 2016 radio flare was also accompanied by radio spectral changes, but was not seen in the X-rays. We model the flare as resulting from the interaction of the nuclear jet with a cloud in the interstellar medium. This is distinct from late-time X-ray flares in a few other TDEs where changes in the accretion state and/or a fallback event were suggested, neither of which appears possible in this case. Our reanalysis of the Swift and XMM-Newton data from 2011 shows significant evidence for thermal emission from a disk, as well as a very soft power-law. This, in addition to the extreme X-ray flux increase seen in 2010 (a factor of >$100) bolsters the identification of IGRJ12580+0134 as a TDE, not an unusual AGN variability event.