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

• Published in: Monthly notices of the Royal Astronomical Society Vol. 530; no. 4; pp. 4501 - 4518
• Main Authors: Hoogendam, W B, Hinkle, J T, Shappee, B J, Auchettl, K, Kochanek, C S, Stanek, K Z, Maksym, W P, Tucker, M A, Huber, M E, Morrell, N, Burns, C R, Hey, D, Holoien, T W -S, Prieto, J L, Stritzinger, M, Do, A, Polin, A, Ashall, C, Brown, P J, DerKacy, J M, Ferrari, L, Galbany, L, Hsiao, E Y, Kumar, S, Lu, J, Stevens, C P
• Format: Journal Article
• Language: English
• Published: 06-05-2024
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stae1121

ABSTRACT
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 ΔL40 ≈ −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.