A Mid-infrared Flare in the Active Galaxy MCG-02-04-026: Dust Echo of a Nuclear Transient Event

TL;DR

This paper reports the discovery of a mid-infrared flare in galaxy MCG-02-04-026, interpreted as a dust echo of a hidden nuclear transient event, revealing insights into obscured energetic phenomena near the galaxy's core.

Contribution

It presents the first detection of a MIR flare in this galaxy and models it as a dust echo, suggesting a previously unobserved nuclear transient event.

Findings

MIR flare peaked around 2015 and faded by 2017

Energy released exceeds 7×10^{50} erg in infrared

Transient event likely produced at least 10^{51} erg, hidden by dust

Abstract

We report the discovery of a mid-infrared (MIR) flare using WISE data in the center of the nearby Seyfert 1.9 galaxy MCG-02-04-026. The MIR flare began in the first half of 2014, peaked around the end of 2015, and faded in 2017. During these years, energy more than $7\times10^{50}$ erg was released in the infrared, and the flare's MIR color was generally turning red. We detected neither optical nor ultraviolet (UV) variation corresponding to the MIR flare based on available data. We explained the MIR flare using a dust echo model in which the radiative transfer is involved. The MIR flare can be well explained as thermal reradiation from dust heated by UV-optical photons of a primary nuclear transient event. Although the transient event was not seen directly due to dust obscuration, we can infer that it may produce a total energy of at least $\sim10^{51}$ erg, most of which was released in less than $\sim$3 years. The nature of the transient event could be a stellar tidal disruption event by the central supermassive black hole (SMBH), or a sudden enhancement of the existing accretion flow onto the SMBH, or a supernova which was particularly bright.