Interstellar propagation effects and the precision of pulsar timing

Abstract

Interstellar propagation effects on the arrival time precision of radio pulsars are simulated. It is found that, for a Kolmogorov electron-density turbulence spectrum, time of arrival pertubations are dominated by dispersion measure variations at radio frequencies above several hundred MHz. Dual-frequency observations can be used to remove dispersion measure variations to obtain submicrosecond residuals. The remaining residuals are highly correlated with the angle-of-arrival variations. Fitting for a nonlambda-squared term does improve the final residuals, although it does not appear to improve the measurement of the astrometric terms of proper motion and parallax. Frequent sampling with a small antenna is better for allowing removal of propagation effects and measuring proper motion and parallax in timing data the coarse sampling with a larger antenna.