The fast transient AT 2023clx in the nearby LINER galaxy NGC 3799 as a tidal disruption of a very low-mass star
P. Charalampopoulos, R. Kotak, T. Wevers, G. Leloudas, T. Kravtsov, M. Pursiainen, P. Ramsden, T. Reynolds, A. Aamer, J. P. Anderson, I. Arcavi, Yongzhi Cai, T. W. Chen, M. Dennefeld, L. Galbany, M. Gromadzki, C. P. Gutiérrez, N. Ihanec, T. Kangas, E. Kankare, Erik C. Kool, A. Lawrence, Peter Lundqvist, L. Makrygianni, S. Mattila, T. E. Müller-Bravo, M. Nicholl, F. Onori, A. Sahu, S. J. Smartt, J. Sollerman, Yanan Wang, D. R. Young
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 ( E ( B − V ) 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 = (1.57 ± 0.19)×10 43 erg s −1 . AT 2023clx displays several distinctive features: first, it rose to peak within 10.4 ± 2.5 days, making it the fastest rising TDE to date. Our SMBH mass estimate of M̄ BH ≈ 10 6.0 M ⊙ –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 λλ 5876,6678 emission features that are typically seen in TDEs. The early, broad (width ∼15 000 km s −1 ) profile of H α matches theoretical expectations from an optically thick outflow. A flat Balmer decrement ( L Hα / L Hβ ∼ 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 ∼6353 Å. 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 H α (−9584 km s −1 ). Its third distinctive feature is the rapid cooling during the first ∼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 (≲0.1 M ⊙ ) 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.