# A New Class of Changing-Look LINERs

## TL;DR

This paper reports the discovery of six changing-look LINERs, a new class of active galactic nuclei that transition from LINERs to broad-line or narrow-line Seyfert 1 states, providing insights into LINER accretion physics.

## Contribution

It introduces a systematic method to identify changing-look LINERs and characterizes their properties, expanding understanding of LINER variability and AGN evolution.

## Key findings

- Six new changing-look LINERs discovered.
- Transformations into broad-line AGN and NLS1 observed.
- Multi-wavelength follow-up reveals dust and X-ray flares.

## Abstract

We report the discovery of six active galactic nuclei (AGN) caught "turning on" during the first nine months of the Zwicky Transient Facility (ZTF) survey. The host galaxies were classified as LINERs by weak narrow forbidden line emission in their archival SDSS spectra, and detected by ZTF as nuclear transients. In five of the cases, we found via follow-up spectroscopy that they had transformed into broad-line AGN, reminiscent of the changing-look LINER iPTF 16bco. In one case, ZTF18aajupnt/AT2018dyk, follow-up HST UV and ground-based optical spectra revealed the transformation into a narrow-line Seyfert 1 (NLS1) with strong [Fe VII, X, XIV] and He II 4686 coronal lines. Swift monitoring observations of this source reveal bright UV emission that tracks the optical flare, accompanied by a luminous soft X-ray flare that peaks ~60 days later. Spitzer follow-up observations also detect a luminous mid-infrared flare implying a large covering fraction of dust. Archival light curves of the entire sample from CRTS, ATLAS, and ASAS-SN constrain the onset of the optical nuclear flaring from a prolonged quiescent state. Here we present the systematic selection and follow-up of this new class of changing-look LINERs, compare their properties to previously reported changing-look Seyfert galaxies, and conclude that they are a unique class of transients well-suited to test the uncertain physical processes associated with the LINER accretion state.