# Discovery and Follow-up of the Unusual Nuclear Transient OGLE17aaj

## TL;DR

OGLE17aaj is a peculiar nuclear transient with properties similar to TDEs but also unique features, suggesting it may be a new type of accretion event in active supermassive black holes.

## Contribution

This paper reports the discovery and detailed follow-up of OGLE17aaj, proposing it as a potential new class of nuclear transient related to accretion events.

## Key findings

- OGLE17aaj exhibits a long 60-day rise and high black-body temperature.
- Its spectral features differ from typical TDEs, with narrow emission lines.
- Historical variability hints at a connection to accretion processes in active galactic nuclei.

## 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.