AT 2020nov: Evidence for Disk Reprocessing in a Rare Tidal Disruption Event

TL;DR

This paper presents a detailed multi-wavelength analysis of AT 2020nov, a rare tidal disruption event with unique spectral features, evidence of disk reprocessing, and a quiescent extended disk around its SMBH, highlighting its significance in TDE studies.

Contribution

It provides the first detailed evidence of disk reprocessing in a TDE with a quiescent, extended disk, enhancing understanding of TDE emission mechanisms in dormant galaxy nuclei.

Findings

Detection of double-peaked Balmer lines and a broad UV/optical flare.

Observation of late-time X-ray flare indicating disk activity.

Spectral modeling reveals an extended quiescent disk around the SMBH.

Abstract

We present a detailed analysis of AT 2020nov, a tidal disruption event (TDE) in the center of its host galaxy, located at a redshift of $z = 0.083$. AT 2020nov exhibits unique features, including double-peaked Balmer emission lines, a broad UV/optical flare, and a peak log luminosity in the extreme ultra-violet (EUV) estimated at $\sim$$45.66^{+0.10}_{-0.33} \; \mathrm{erg} \, \mathrm{s^{-1}}$. A late-time X-ray flare was also observed, reaching an absorbed luminosity of $1.67 \times 10^{43} \; \mathrm{erg} \, \mathrm{s^{-1}}$ approximately 300 days after the UV/optical peak. Multi-wavelength coverage, spanning optical, UV, X-ray, and mid-infrared (MIR) bands, reveals a complex spectral energy distribution (SED) that includes MIR flaring indicative of dust echoes, suggesting a dust covering fraction consistent with typical TDEs. Spectral modeling indicates the presence of an extended, quiescent disk around the central supermassive black hole (SMBH) with a radius of $\sim$$5.06^{+0.59}_{-0.77} \times 10^4 \; \mathrm{R_g}$. The multi-component SED model, which includes a significant EUV component, suggests that the primary emission from the TDE is reprocessed by this extended disk, producing the observed optical and MIR features. The lack of strong AGN signatures in the host galaxy, combined with the quiescent disk structure, highlights AT 2020nov as a rare example of a TDE occurring in a galaxy with a dormant but extended pre-existing accretion structure.