  We have carried out a continuous multi-band photometric monitoring of the
nuclear activity of comet 29P/Schwassmann-Wachmann 1 from 2008 to 2010. Our
main aim has been to study the outburst mechanism on the basis of a follow-up
of the photometric variations associated with the release of dust. We used a
standardized method to obtain the 10 arc-sec nucleus photometry in the V, R,
and I filters of the Johnson-Kron-Cousins system, being accurately calibrated
with standard Landolt stars. Production of dust in the R and I bands during the
2010 Feb. 3 outburst has been also computed. We conclude that the massive
ejection of large (optically-thin) particles from the surface at the time of
the outburst is the triggering mechanism to produce the outburst. Ulterior
sublimation of these ice-rich dust particles during the following days induces
fragmentation, generating micrometer-sized grains that increase the dust
spatial density to produce the outburst in the optical range due to scattering
of sun light. The material leaving the nucleus adopts a fan-like dust feature,
formed by micrometer-sized particles that are decaying in brightness as it
evolved outwards. By analyzing the photometric signal measured in a
standardized 10-arcsec aperture using the Phase Dispersion Minimization
technique we have found a clear periodicity of 50 days. Remarkably, this value
is also consistent with an outburst frequency of 7.4 outbursts/year deduced
from the number of outbursts noticed during the effective observing time.
