  Detailed studies of AC velocity Vac and temperature dependence of torsional
oscillator responses of solid 4He are reported. A characteristic onset
temperature T0 about 0.5 K is found, below which a significant Vac dependent
change occurs in the energy dissipation for the sample at 32 bar. A Vac
dependence of the non-classical rotational inertia fraction, NCRIF also appears
below about T0. This value of T0 excludes the possible explanation of
supersolid by liquid superfluidity in grain boundaries or other liquid related
origins. The log(Vac) linear dependence was found in NCRIF. Furthermore, this
linear slope changes in proportion to 1/T 2 for 40 < Vac < 400 micro-m/s, then
crosses over to about 1/T for larger Vac. We discuss properties of the vortex
fluid state proposed by Anderson above Tc, below T0.
