  An exact analytic solution for the dynamics of vortex pairs is obtained for
rapid temperature quenches of a superfluid film starting from the line of
critical points below the critical temperature $T_{KT}$. An approximate
solution for quenches at and above above $T_{KT}$ provides insights into the
origin of logarithmic transients in the vortex decay, and are in general
agreement with recent simulations of the quenched XY model. These results
confirm that there is no "creation" of vortices whose density increases with
the quench rate as predicted by the Kibble-Zurek theory, but only monotonic
decay of the thermal vortices already present at the initial temperature.
