  Spatiotemporal techniques for signal coordination with actively transmitting
extraterrestrial civilizations, without the need for prior communication, can
constrain technosignature searches to a significantly smaller coordinate space.
With the variable star catalog from Gaia Data Release 3, we explore two related
signaling strategies: the SETI Ellipsoid, and that proposed by Seto, which are
both based on the synchronization of transmissions with a conspicuous
astrophysical event. This dataset contains more than 10 million variable star
candidates with light curves from the first three years of Gaia's operational
phase, between 2014 and 2017. Using four different historical supernovae as
source events, we find that less than 0.01% of stars in the sample have
crossing times, the times at which we would expect to receive synchronized
signals on Earth, within the date range of available Gaia observations. For
these stars, we present a framework for technosignature analysis that searches
for modulations in the variability parameters by splitting the stellar light
curve at the crossing time.
