  We consider a thermalization process in a 2-dimensional CFT that has a
holographic description in terms of the gravitational collapse of a thin shell
of null dust. This model represents a sudden perturbation of the CFT vacuum
that communicates a uniform energy density to the system. We study the
evolution of two-point functions at spacelike separated points (t1,l) and
(t2,0), and reproduce the generic pattern first derived from the analysis of
quantum quenches to critical systems. A crucial characteristic of these setups
is that the excitations generated by the initial perturbation presents
non-trivial quantum correlations. As a consequence, for any ti<infinity
equilibration is only effective on finite regions whose size grows as a
lightfront. The behavior on larger regions is greatly determined by the initial
state, which for the quenches we consider and the holographic model has
relevant differences. However in both cases for late times the dependence on
the scale l of the two-point functions enters through the effective distance
l-t1-t2. We interpret the onset of this behavior as an equilibration time for
occupation numbers in these 2-dimensional models.
