H-I line measurements of pulsars towards the Galactic Centre and the electron density in the inner Galaxy

We have measured 21-cm absorption and emission spectra in the direction of a further seven southern pulsars with the Parkes telescope to derive their kinematic distances and to study the interstellar medium. For the first tim e we have successfully obtained HI absorption measurements for PSRs J1602-5 100, J1740-3015 and J1745-3040. We have also significantly improved the sen sitivity and resolution on PSRs J1600-5044, J1752-2806 and J1825-0935, the spectra of which have previously been measured, and have corrected an error in the published distance to PSR J1824-1945. Since the Frail & Weisberg summary of pulsar distances in 1990, a further 2 3 pulsars now have measured H I distances, mainly through the efforts of th e current group. We discuss the Taylor & Cordes electron density model in l ight of these new measurements and find that, although the model towards th e Galactic Centre appears good, the line of sight through the Carina spiral arm is poorly fitted by the model.