TY - JOUR KW - Black hole physics KW - gravitational waves KW - galaxies: nuclei KW - ultraviolet: general KW - transients: tidal disruption events N1 - This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third-party material in this article are included in the Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ IS - 2 EP - 1710 TI - Swift/UVOT discovery of Swift J221951?484240: a UV luminous ambiguous nuclear transient AV - public JF - Monthly Notices of the Royal Astronomical Society PB - Oxford University Press (OUP) A1 - Oates, SR A1 - Kuin, NPM A1 - Nicholl, M A1 - Marshall, F A1 - Ridley, E A1 - Boutsia, K A1 - Breeveld, AA A1 - Buckley, DAH A1 - Cenko, SB A1 - De Pasquale, M A1 - Edwards, PG A1 - Gromadzki, M A1 - Gupta, R A1 - Laha, S A1 - Morrell, N A1 - Orio, M A1 - Pandey, SB A1 - Page, MJ A1 - Page, KL A1 - Parsotan, T A1 - Rau, A A1 - Schady, P A1 - Stevens, J A1 - Brown, PJ A1 - Evans, PA A1 - Gronwall, C A1 - Kennea, JA A1 - Klingler, NJ A1 - Siegel, MH A1 - Tohuvavohu, A A1 - Ambrosi, E A1 - Barthelmy, SD A1 - Beardmore, AP A1 - Bernardini, MG A1 - Bonnerot, C A1 - Campana, S A1 - Caputo, R A1 - Ciroi, S A1 - Cusumano, G A1 - Aì, AD A1 - Avanzo, PD A1 - Elia, VD A1 - Giommi, P A1 - Hartmann, DH A1 - Krimm, HA A1 - Malesani, DB A1 - Melandri, A A1 - Nousek, JA A1 - Brien, PTO A1 - Osborne, JP A1 - Pagani, C A1 - Palmer, DM A1 - Perri, M A1 - Racusin, JL A1 - Sakamoto, T A1 - Sbarufatti, B A1 - Schlieder, JE A1 - Tagliaferri, G A1 - Troja, E A1 - Xu, D VL - 530 SP - 1688 N2 - We report the discovery of Swift J221951?484240 (hereafter: J221951), a luminous slow-evolving blue transient that was detected by the Neil Gehrels Swift Observatory Ultraviolet/Optical Telescope (Swift/UVOT) during the follow-up of gravitational wave alert S190930t, to which it is unrelated. Swift/UVOT photometry shows the UV spectral energy distribution of the transient to be well modelled by a slowly shrinking blackbody with an approximately constant temperature of T ? 2.5 × 104 K. At a redshift z = 0.5205, J221951 had a peak absolute magnitude of Mu,AB = ?23 mag, peak bolometric luminosity Lmax = 1.1 × 1045 erg s?1 and a total radiated energy of E > 2.6 × 1052 erg. The archival Wide-field Infrared Survey Explorer IR photometry shows a slow rise prior to a peak near the discovery date. Spectroscopic UV observations display broad absorption lines in N V and O VI, pointing towards an outflow at coronal temperatures. The lack of emission in the higher H ? lines, N I and other neutral lines is consistent with a viewing angle close to the plane of the accretion or debris disc. The origin of J221951 cannot be determined with certainty but has properties consistent with a tidal disruption event and the turn-on of an active galactic nucleus. UR - http://dx.doi.org/10.1093/mnras/stae795 ID - discovery10192060 Y1 - 2024/05/01/ ER -