Probing Pulsar Dispersion Measures using the GMRT

We present the results from a novel experiment for accurate estimation of pulsar dispersion measure (1 part in 10⁴) using the GMRT, without requiring any absolute timing information. The observations were carried out over a period of more than one year for a sample of twelve pulsars. We have used the simultaneous multi-frequency capability of the GMRT. Most of the sample pulsars studied show dispersion measure (DM) variations on time scales of weeks to months. The mean DM value for some of the pulsars show a significant discrepancy with respect to the catalog value. Pulsar B2217+47 shows a large-scale DM gradient over a one year period. For some pulsars we find small differences in the DM values obtained from different frequency combinations.