Hello Darkness My Old Friend: The Fading of the Nearby TDE ASASSN-14ae

TL;DR

This study tracks the optical evolution of the nearby TDE ASASSN-14ae over 750 days, revealing that optical emission can fade within a year, impacting detection strategies and understanding of TDE host galaxies.

Contribution

It provides the most stringent late-time Hα luminosity limits for a TDE, demonstrating the rapid fading of optical emission and informing future detection and analysis methods.

Findings

Hα emission weakens significantly 300 days after discovery

Hα luminosity drops below 10^39 ergs s^-1 around 750 days

Optical emission from TDEs can vanish within approximately one year

Abstract

We present late-time optical spectroscopy taken with the Large Binocular Telescope's Multi-Object Double Spectrograph, an improved ASAS-SN pre-discovery non-detection, and late-time SWIFT observations of the nearby ($d=193$ Mpc, $z=0.0436$) tidal disruption event (TDE) ASASSN-14ae. Our observations span from $\sim$20 days before to $\sim$750 days after discovery. The proximity of ASASSN-14ae allows us to study the optical evolution of the flare and the transition to a host dominated state with exceptionally high precision. We measure very weak H$\alpha$ emission 300 days after discovery ($L_{\rm H\alpha} \simeq 4\times 10^{39}$ ergs s$^{-1}$) and the most stringent upper limit to date on the H$\alpha$ luminosity $\sim$750 days after discovery ($L_{\rm H\alpha} \lesssim 10^{39}$ ergs s$^{-1}$), suggesting that the optical emission arising from a TDE can vanish on a timescale as short as 1 year. Our results have important implications for both spectroscopic detection of TDE candidates at late times, as well as the nature of TDE host galaxies themselves.