We show the results of our analysis of the pulse broadening phenomenon in 25 pulsars at several frequencies using the data gathered with GMRT and Effelsberg radiotelescopes. Twenty two of these pulsars were not studied in that regard before and our work has increased the total number of pulsars with multi-frequency scattering measurements to almost 50, basically doubling the amount available so far. The majority of the pulsars we observed have high to very-high dispersion measures (DM > 200) and our results confirm the suggestion of Löhmer et al. (2001, 2004) that the scatter time spectral indices for high-DM pulsars deviate from the value predicted by a single thin screen model with Kolmogorov's distribution of the density fluctuations. In this paper we discuss the possible explanations for such deviations.

We study the radio spectrum of PSR B1259−63 orbiting around the Be star LS 2883 and show that the shape of the spectrum depends on the orbital phase. At frequencies below 3 GHz, PSR B1259−63 flux densities are lower when measured near the periastron passage than those measured far from periastron. We suggest that an interaction of the radio waves with the Be star environment accounts for this effect. While it is quite natural to explain the pulsar eclipse by the presence of an equatorial disc around LS 2883, this disc alone cannot be responsible for the observed spectral evolution of PSR B1259−63 and we, therefore, propose a qualitative model which explains this evolution. We consider two mechanisms that might influence the observed radio emission: free-free absorption and cyclotron resonance. We believe that this binary system can hold the clue to the understanding of gigahertz-peaked spectra of pulsars.

In this paper we present results from flux density measurements for 21 pulsars over a wide frequency range, using the Giant Metrewave Radio Telescope (GMRT) and the Effelsberg telescope. Our sample was a set of mostly newly discovered pulsars from the selection of candidates for gigahertz-peaked spectra (GPS) pulsars. Using the results of our observations along with previously published data, we identify two new GPS pulsars. One of them, PSR J1740+1000, with dispersion measure of 24 pc cm −3 , is the first GPS pulsar with such a low DM value. We also selected several strong candidates for objects with high frequency turnover in their spectra which require further investigation. We also revisit our source selection criteria for future searches for GPS pulsars.