Tracking pulsar dispersion measures using the GMRT

Abstract

We present preliminary results from an ongoing program of accurate pulsar dispersion measure (DM) measurements using the GMRT. From simultaneous dual frequency observations, we are able to determine OMs to accuracies of 1 part in 104 and better. For 4 of the 12 pulsars studied, we find our mean DM value to be significantly different from the expected value. For most of the pulsars, we detect significant variations of the DM on time scales of weeks to months.