To TDE or not to TDE: the luminous transient ASASSN-18jd with TDE-like and AGN-like qualities
Gromadzki, M.; Kochanek, C. S.; Foley, R. J.; Huber, M. E.; Pogge, R. W.; Stanek, K. Z.; Dong, Subo; Buckley, D. A. H.; Shappee, B. J.; Tucker, M. A.; Do, A.; Ricci, C.; Kilpatrick, C. D.; Brown, J. S.; Holoien, T. W. -S.; Prieto, J. L.; Drout, M. R.; Neustadt, J. M. M.; Payne, A. V.; Auchettl, K.; Coulter, D. A.; Piro, A. L.; Siebert, M. R.; Rojas-Bravo, C.; Bose, S.; Dimitriadis, G.; Vallely, P. J.; Chen, Ping; Thompson, T. A.
United States, Denmark, China, Chile, Canada, South Africa, Poland
Abstract
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 $T \sim 2.5 \times 10^{4} \, {\rm K}$ , a maximum observed luminosity of $L_{\rm max} = 4.5^{+0.6}_{-0.3}\times 10^{44} \, {\rm erg \,s}^{-1}$ , and a radiated energy of $E = 9.6^{+1.1}_{-0.6} \times 10^{51} \, {\rm erg}$ . 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).