  The Zwicky Transient Facility (ZTF) has discovered five new events belonging
to an emerging class of AGN undergoing smooth flares with large amplitudes and
rapid rise times. This sample consists of several transients that were
initially classified as supernovae with narrow spectral lines. However, upon
closer inspection, all of the host galaxies display resolved Balmer lines
characteristic of a narrow-line Seyfert 1 (NLSy1) galaxy. The transient events
are long-lived, over 400 days on average. We report UV and X-ray follow-up of
the flares and observe persistent UV-bright emission, with two of the five
transients detected with luminous X-ray emission, ruling out a supernova
interpretation. We compare the properties of this sample to previously reported
flaring NLSy1 galaxies, and find that they fall into three spectroscopic
categories: Transients with 1) Balmer line profiles and Fe II complexes typical
of NLSy1s, 2) strong He II profiles, and 3) He II profiles including Bowen
fluorescence features. The latter are members of the growing class of AGN
flares attributed to enhanced accretion reported by Trakhtenbrot et al. (2019).
We consider physical interpretations in the context of related transients from
the literature. For example, two of the sources show high amplitude
rebrightening in the optical, ruling out a simple tidal disruption event
scenario for those transients. We conclude that three of the sample belong to
the Trakhtenbrot et al. (2019) class, and two are TDEs in NLSy1s. We also aim
to understand why NLSy1s are preferentially the sites of such rapid enhanced
flaring activity.
