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Discovery and Follow-up of the Unusual Nuclear Transient OGLE17aaj

Authors :: Gromadzki, M.
Hamanowicz, A.
Wyrzykowski, L.
Sokolovsky, K. V.
Fraser, M.
Kozlowski, Sz.
Guillochon, J.
Arcavi, I.
Trakhtenbrot, B.
Jonker, P. G.
Mattila, S.
Udalski, A.
Szymanski, M. K.
Soszynski, I.
Poleski, R.
Pietrukowicz, P.
Skowron, J.
Mroz, P.
Ulaczyk, K.
Pawlak, M.
Rybicki, K. A.
Sollerman, J.
Taddia, F.
Kostrzewa-Rutkowska, Z.
Onori, F.
Young, D. R.
Maguire, K.
Smartt, S. J.
Inserra, C.
Gal-Yam, A.
Rau, A.
Chen, T. -W.
Angus, C. R.
Buckley, D. A. H.
Publication Year :: 2019
Abstract: We report on the discovery and follow-up of a peculiar transient, OGLE17aaj, which occurred in the nucleus of a weakly active galaxy. We investigate whether it can be interpreted as a new candidate for a tidal disruption event (TDE). We present the OGLE-IV light curve that covers the slow 60-day-long rise to maximum along with photometric, spectroscopic, and X-ray follow-up during the first year. OGLE17aaj is a nuclear transient exhibiting some properties similar to previously found TDEs, including a long rise time, lack of colour-temperature evolution, and high black-body temperature. On the other hand, its narrow emission lines and slow post-peak evolution are different from previously observed TDEs. Its spectrum and light-curve evolution is similar to F01004-2237 and AT 2017bgt. Signatures of historical low-level nuclear variability suggest that OGLE17aaj may instead be related to a new type of accretion event in active super-massive black holes.<br />Comment: 5 pages, 3 figures, accepted for publication in Astronomy & Astrophysics as Letter to Editor