Discovery and follow-up of ASASSN-23bd (AT 2023clx): the lowest redshift and luminosity optically selected tidal disruption event.

We report the All-Sky Automated Survey for SuperNovae discovery of the tidal disruption event (TDE) ASASSN-23bd (AT 2023clx) in NGC 3799, a LINER galaxy with no evidence of strong active galactic nucleus (AGN) activity over the past decade. With a redshift of z  = 0.01107 and a peak ultraviolet (UV)/optical luminosity of (5.4 ± 0.4) × 10⁴² erg s⁻¹, ASASSN-23bd is the lowest-redshift and least-luminous TDE discovered to date. Spectroscopically, ASASSN-23bd shows H α and He  i emission throughout its spectral time series, there are no coronal lines in its near-infrared spectrum, and the UV spectrum shows nitrogen lines without the strong carbon and magnesium lines typically seen for AGN. Fits to the rising ASAS-SN light curve show that ASASSN-23bd started to brighten on MJD 59988 |$^{+1}_{-1}$|⁠ , ∼9 d before discovery, with a nearly linear rise in flux, peaking in the g band on MJD |$60 \, 000^{+3}_{-3}$|⁠. Scaling relations and TDE light curve modelling find a black hole mass of ∼10⁶ M_⊙, which is on the lower end of supermassive black hole masses. ASASSN-23bd is a dim X-ray source, with an upper limit of |$L_{0.3-10\, \mathrm{keV}} \lt 1.0\times 10^{40}$| erg s⁻¹ from stacking all Swift observations prior to MJD 60061, but with soft (∼0.1 keV) thermal emission with a luminosity of |$L_{0.3-2 \, \mathrm{keV}}\sim 4\times 10^{39}$| erg s⁻¹ in XMM-Newton observations on MJD 60095. The rapid (t < 15 d) light curve rise, low UV/optical luminosity, and a luminosity decline over 40 d of Δ L ₄₀ ≈ −0.7 dex make ASASSN-23bd one of the dimmest TDEs to date and a member of the growing 'Low Luminosity and Fast' class of TDEs. [ABSTRACT FROM AUTHOR]