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

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...

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Bibliographic Details
Published in:	Monthly notices of the Royal Astronomical Society 2020-05, Vol.494 (2), p.2538-2560
Main Authors:	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, Thompson, T A, 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
Format:	Article
Language:	eng
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Summary:	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).
ISSN:	0035-8711 1365-2966