We report here on variable propagation effects in over twenty years of multi-frequency timing analysis of pulsar PSR B1937+21 that determine small-scale properties of the intervening plasma as it drifts through the sight line .
The phase structure function derived from the dispersion measure variations is in remarkable agreement with that expected from the Kolmogorov spectrum , with a power law index of 3.66 \pm 0.04 , valid over an inferred scale range of 0.2—50 A.U .
The observed flux variation time scale and the modulation index , along with their frequency dependence , are discrepant with the values expected from a Kolmogorov spectrum with infinitismally small inner scale cutoff , suggesting a caustic-dominated regime of interstellar optics .
This implies an inner scale cutoff to the spectrum of \sim 1.3 \times 10 ^ { 9 } meters .
Our timing solutions indicate a transverse velocity of 9 km sec ^ { -1 } with respect to the solar system barycenter , and 80 km sec ^ { -1 } with respect to the pulsar ’ s LSR .
We interpret the frequency dependent variations of DM as a result of the apparent angular broadening of the source , which is a sensitive function of frequency ( \propto \nu ^ { -2.2 } ) .
The error introduced by this in timing this pulsar is \sim 2.2 \mu s at 1 GHz .
The timing error introduced by ‘ ‘ image wandering ’ ’ from the slow , nominally refractive scintillation effects is about 125 nanosec at 1 GHz .
The error accumulated due to positional error ( due to image wandering ) in solar system barycentric corrections is about 85 nanosec at 1 GHz .