  We show using numerical simulations that slowly driven skyrmions interacting
with random pinning move via correlated jumps or avalanches. The avalanches
exhibit power law distributions in their duration and size, and the average
avalanche shape for different avalanche durations can be scaled to a universal
function, in agreement with theoretical predictions for systems in a
nonequilibrium critical state. A distinctive feature of skyrmions is the
influence of the non-dissipative Magnus term. When we increase the ratio of the
Magnus term to the damping term, a change in the universality class of the
behavior occurs, the average avalanche shape becomes increasingly asymmetric,
and individual avalanches exhibit motion in the direction perpendicular to
their own density gradient.
