  Recent theories and experiments have suggested hydrodynamic phonon transport
features in graphite at unusually high temperatures. Here, we report a
pico-second pump-probe thermal reflectance measurement of heat pulse
propagation in graphite. The measurement results reveal transient lattice
cooling near the adiabatic center of a 15 $\mu$m diameter ring-shape pump beam
at temperatures between 80 and 120 K. While such lattice cooling has not been
reported in recent diffraction measurements of second sound in graphite, the
observation here is consistent with both hydrodynamic phonon transport theory
and prior heat pulse measurements of second sound in bulk sodium fluoride.
