Anomalous scattering of highly dispersed pulsars

We report multifrequency measurements of scatter-broadening times for nine highly dispersed pulsars over a wide frequency range (0.6-4.9 GHz). We find the scatter-broadening times to be larger than expected and to scale with frequency with an average power-law index of 3.44 +/- 0.13, i.e., significantly less than that expected from standard theories. Such possible discrepancies have been predicted very recently by Cordes and Lazio.