To TDE or not to TDE: the luminous transient ASASSN-18jd with TDE-like and AGN-like qualities

Neustadt, J. M. M.; Holoien, T. W-S; Kochanek, C. S.; Auchettl, K.; Brown, J. S.; Shappee, B. J.; Pogge, R. W.; Dong, Subo; Stanek, K. Z.; Tucker, M. A.; Bose, S.; Chen, Ping; Ricci, C.; Vallely, P. J.; Prieto, J. L.; Coulter, D. A.; Drout, M. R.; Foley, R. J.; Kilpatrick, C. D.; Piro, A. L.; Rojas-Bravo, C.; Buckley, D. A. H.; Gromadzki, M.; Dimitriadis, G.; Siebert, M. R.; Do, A.; Huber, M. E.; Payne, A., V
2020
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
DOI
10.1093/mnras/staa859
We present the discovery of ASASSN-18jd (AT 2018bcb), a luminous optical/ultraviolet(UV)/X-ray transient located in the nucleus of the galaxy 2MASX J22434289-1659083 at z = 0.1192. Over the year after discovery, Swift UltraViolet and Optical Telescope (UVOT) photometry shows the UV spectral energy distribution of the transient to be well modelled by a slowly shrinking blackbody with temperature T similar to 2.5 x 10(4) K, a maximum observed luminosity of L-max = 4.5(-0.3)(+0.6) x 10(44) erg s(-1), and a radiated energy of E = 9.6(-0.6)(+1.1) x 10(51) erg. X-ray data from Swift X-Ray Telescope (XRT) and XMM Newton show a transient, variable X-ray flux with blackbody and power-law components that fade by nearly an order of magnitude over the following year. Optical spectra show strong, roughly constant broad Balmer emission and transient features attributable to He II, N III-V O III, and coronal Fe. While ASASSN-18jd shares similarities with tidal disruption events (TDEs), it is also similar to the newly discovered nuclear transients seen in quiescent galaxies and faint active galactic nuclei (AGNs).