  With the help of a statistical parameter derived from optical spectra, we
show that the current star formation rate of a galaxy, falling into a cluster
along a supercluster filament, is likely to undergo a sudden enhancement before
the galaxy reaches the virial radius of the cluster. From a sample of 52
supercluster-scale filaments of galaxies joining a pair of rich clusters of
galaxies within the two-degree Field Redshift Survey region, we find a
significant enhancement of star formation, within a narrow range between 2-3
h/70 Mpc of the centre of the cluster into which the galaxy is falling. This
burst of star formation is almost exclusively seen in the fainter dwarf
galaxies (M_B> -20). The relative position of the peak does not depend on
whether the galaxy is a member of a group or not, but non-group galaxies have
on average a higher rate of star formation immediately before falling into a
cluster. From the various trends, we conclude that the predominant process
responsible for this rapid burst is the close interaction with other galaxies
falling into the cluster along the same filament, if the interaction occurs
before the gas reservoir of the galaxy gets stripped off due to the interaction
with the intracluster medium.
