Letter to the Editor

Discovery and follow-up of the unusual nuclear transient OGLE17aaj

¹ Warsaw University Astronomical Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
e-mail: marg@astrouw.edu.pl
² European Southern Observatory, Karl Schwarzschild Str 2, 85748 Garching, Germany
³ IAASARS, National Observatory of Athens, Vas. Pavlou & I. Metaxa, Penteli 15236, Greece
⁴ Sternberg Astronomical Institute, Moscow State University, Universitetsky pr. 13, Moscow 119991, Russia
⁵ Lebedev Physical Institute, Astro Space Center, Profsoyuznaya 84/32, Moscow 117997, Russia
⁶ School of Physics, O’Brien Centre for Science North, University College Dublin, Belfield Dublin 4, Ireland
⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
⁸ Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
⁹ Las Cumbres Observatory, 6740 Cortona Dr Ste 102, Goleta, CA 93117-5575, USA
¹⁰ The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
¹¹ Department of Physics, ETH Zurich, Wolgang-Pauli-Str. 27, Zurich 8093, Switzerland
¹² SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
¹³ Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands
¹⁴ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Väisäläntie 20, 21500 Piikkiaö, Finland
¹⁵ Ohio State University, Department of Astronomy, 140 West 18th Avenue, Columbus, OH 43210, USA
¹⁶ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹⁷ Department of Astronomy, The Oskar Klein Center, Stockholm University, AlbaNova 10691, Stockholm, Sweden
¹⁸ Astrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN, UK
¹⁹ School of Physics & Astronomy, University of Southampton, Southampton SO17 1BJ, UK
²⁰ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, 234 Herzl St., Rehovot, Israel
²¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstr. 1, 85748 Garching, Germany
²² South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa

Received: 20 June 2018
Accepted: 4 January 2019

Abstract

Aims. 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).

Methods. 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.

Results. 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.