SCAT Uncovers ATLAS's First Tidal Disruption Event ATLAS18mlw: A Faint and Fast TDE in a Quiescent Balmer Strong Galaxy

TL;DR

This paper reports the discovery and detailed analysis of ATLAS18mlw, a faint and fast tidal disruption event in a quiescent galaxy, highlighting its unique properties and contribution to the understanding of low-luminosity TDEs.

Contribution

The study presents the first detailed characterization of a faint, fast TDE using multi-year optical data and spectral analysis, expanding knowledge of TDE diversity.

Findings

ATLAS18mlw is a low-luminosity TDE with a peak luminosity of 10^43.5 erg/s.

The event declined rapidly, with a decline rate of -0.7 dex over 40 days.

The host galaxy is quiescent and Balmer strong, supporting the TDE classification.

Abstract

We present the discovery that ATLAS18mlw was a tidal disruption event (TDE) in the galaxy WISEA J073544.83+663717.3, at a luminosity distance of 334 Mpc. Initially discovered by the Asteroid Terrestrial Impact Last Alert System (ATLAS) on 2018 March 17.3, the TDE nature of the transient was uncovered only recently with the re-reduction of a SuperNova Integral Field Spectrograph (SNIFS) spectrum. This spectrum, taken by the Spectral Classification of Astronomical Transients (SCAT) survey, shows a strong blue continuum and a broad H$\alpha$ emission line. Here we present roughly six years of optical survey photometry beginning before the TDE to constrain AGN activity, optical spectroscopy of the transient, and a detailed study of the host galaxy properties through analysis of archival photometry and a host spectrum. ATLAS18mlw was detected in ground-based light curves for roughly two months. From a blackbody fit to the transient spectrum and bolometric correction of the optical light curve, we conclude that ATLAS18mlw is best explained by a low-luminosity TDE with a peak luminosity of log(L [erg s$^{-1}$]) = $43.5 \pm 0.2$. The TDE classification is further supported by the quiescent Balmer strong nature of the host galaxy. We also calculated the TDE decline rate from the bolometric light curve and find $\Delta L_{40} = -0.7 \pm 0.2$ dex, making ATLAS18mlw a member of the growing class of ``faint and fast'' TDEs with low peak luminosities and fast decline rates.