The fast transient AT 2023clx in the nearby LINER galaxy NGC 3799 as a tidal disruption of a very low-mass star

Abstract

We present an extensive analysis of the optical and ultraviolet (UV) properties of AT 2023clx, the closest optical/UV tidal disruption event (TDE) to date ($z=0.01107$), which occurred in the nucleus of the interacting low-ionization nuclear emission-line region (LINER) galaxy, NGC 3799. After correcting for the host reddening ($ h $ = 0.179 mag), we find its peak absolute $g$-band magnitude to be $-18.03 0.07$ mag, and its peak bolometric luminosity to be L_ pk $. AT 2023clx displays several distinctive features: first, it rose to peak within $10.4 days, making it the fastest rising TDE to date. Our SMBH mass estimate of $ M BH ---estimated using several standard methods--- rules out the possibility of an intermediate-mass BH as the reason for the fast rise. Dense spectral follow-up reveals a blue continuum that cools slowly and broad Balmer and He II lines as well as weak He I emission features that are typically seen in TDEs. The early, broad (width $ $) profile of Halpha matches theoretical expectations from an optically thick outflow. A flat Balmer decrement ($L_ H alpha $/$L_ H beta 1.58$) suggests that the lines are collisionally excited rather than being produced via photoionisation, in contrast to typical active galactic nuclei. A second distinctive feature, seen for the first time in TDE spectra, is a sharp, narrow emission peak at a rest wavelength of sim 6353 This feature is clearly visible up to 10\,d post-peak; we attribute it to clumpy material preceding the bulk outflow, which manifests as a high-velocity component of Halpha ($-9\,584 $). Its third distinctive feature is the rapid cooling during the first sim 20 days after peak, reflected as a break in the temperature evolution. Combining these findings, we propose a scenario for AT 2023clx involving the disruption of a very low-mass star ($ with an outflow launched in our line of sight and with disruption properties that led to efficient circularisation and prompt accretion disc formation, observed through a low-density photosphere.