  Transient accretion events onto supermassive black holes (SMBHs), such as
tidal disruption events (TDEs), Bowen Fluorescence Flares (BFFs), and active
galactic nuclei (AGNs), which are accompanied by sudden increases of activity,
offer a new window onto the SMBH population, accretion physics, and stellar
dynamics in galaxy centers. However, such transients are rare and finding them
in wide-field transient surveys is challenging. Here we present the results of
a systematic real-time search for SMBH-related transients in Zwicky Transient
Facility (ZTF) public alerts, using various search queries. We examined 345
rising events coincident with a galaxy nucleus, with no history of previous
activity, of which 223 were spectroscopically classified. Of those, five (2.2%)
were TDEs, one (0.5%) was a BFF, and two (0.9%) were AGN flares. Limiting the
search to blue events, the fraction of TDEs nearly doubles to 4.1%, and no TDEs
are missed. Limiting the search further to candidate post-starburst galaxies
increases the relative number of TDEs to 16.7%, but the absolute numbers in
such a search are small. The main contamination source is supernovae (95.1% of
classified events), of which the majority (82.2% of supernovae) are of Type Ia.
In a comparison set of 39 events with limited photometric history, the AGN
contamination increases to ~30%. Host galaxy offset is not a significant
discriminant of TDEs in current ZTF data, but might be useful in
higher-resolution data. Our results can be used to quantify the efficiency of
various SMBH-related transient search strategies in optical surveys such as ZTF
and the Legacy Survey of Space and Time.
