  Galaxies that abruptly interrupt their star formation in < 1.5 Gyr present
recognizable features in their spectra (no emission and Hd in absorption) and
are called post starburst (PSB) galaxies. By studying their stellar population
properties and their location within the clusters, we obtain valuable insights
on the physical processes responsible for star formation quenching. We present
the first complete characterization of PSB galaxies in clusters at 0.04 < z <
0.07, based on WINGS and OmegaWINGS data, and contrast their properties to
those of passive (PAS) and emission line (EML) galaxies. For V < 20, PSBs
represent 7.2 +/- 0.2% of cluster galaxies within 1.2 virial radii. Their
incidence slightly increases from the outskirts toward the cluster center and
from the least toward the most luminous and massive clusters, defined in terms
of X-ray luminosity and velocity dispersion. The phase-space analysis and
velocity dispersion profile suggest that PSBs represent a combination of
galaxies with different accretion histories. Moreover, PSBs with the strongest
Hd are consistent with being recently accreted. PSBs have stellar masses,
magnitudes, colors and morphologies intermediate between PAS and EML galaxies,
typical of a population in transition from being star forming to passive.
Comparing the fraction of PSBs to the fraction of galaxies in transition on
longer timescales, we estimate that the short timescale star-formation
quenching channel contributes two times more than the long timescale one to the
growth of the passive population. Processes like ram-pressure stripping and
galaxy-galaxy interactions are more efficient than strangulation in affecting
star formation.
