2004A&A...425..569L

In this paper we report multi-frequency measurements of pulse broadening times (τ_d) for nine medium dispersion measure (DM≃150-400pc/cm³) pulsars observed over a wide frequency range. The low frequency data at 243, 325 and 610MHz are new observations done with the Giant Metrewave Radio Telescope (GMRT). The frequency dependence of τ_d for all but one (PSR B1933+16) of our sources is consistent with the Kolmogorov spectrum of electron density fluctuations in a turbulent medium. PSR B1933+16, however, shows a very flat spectrum as previously observed for high DM pulsars. Our observations combined with earlier published results enable us to study the spectral index of τ_d over the whole observed DM range. While the spectral properties are generally consistent with a Kolmogorov spectrum, pulsars seen along line-of-sights towards the inner Galaxy or complex regions often show deviations from this expected behaviour.