  The Gaia third Data Release (DR3) presents a catalogue of 474\,026 stars with
variability induced by magnetic activity. For each star, the catalogue provides
a list of about 70 parameters among which the most important are the stellar
rotation period $P$, the photometric amplitude $A$ of the rotational signal and
the Pearson Correlation Coefficient $r_0$ between brightness and magnitude
variations. The Specific Objects Study (SOS) pipeline, developed to
characterise magnetically active stars with Gaia Data, has been described in
the paper accompanying the Gaia second Data Release. Here we describe the
changes made to the pipeline and a new method developed to analyze Gaia
time-series and to reveal spurious signals induced by instrumental effects or
by the peculiar nature of the investigated stellar source. The period-amplitude
diagram obtained with the DR3 data confirms the bimodal distribution of fast
rotating stars seen in the DR2 release. The DR3 data permitted, for the first
time, to analyze the patterns of magnitude-color variations for thousands of
magnetically active stars. The measured $r_0$ values are tightly correlated
with the stars position in the period-amplitude diagram. The relationship
between the $P$, $A$ and $r_0$ parameters inferred for thousands of stars could
be very useful to improve the understanding of stellar magnetic fields and to
improve theoretical models. The method developed to reveal the spurious signals
can be applied to each of the released Gaia photometric time-series and can be
exploited by anyone interested in working directly with Gaia time-series.
