Multifrequency Observations of Radio Pulse Broadening and Constraints on Interstellar Electron Density Microstructure

We have made observations of 98 low-Galactic-latitude pulsars to measure pulse broadening caused by multipath propagation through the interstellar medium. Data were collected with the 305-m Arecibo telescope at four radio frequencies between 430 and 2380 MHz. We used a CLEAN-based algorithm to deconvolve interstellar pulse broadening from the measured pulse shapes. We employed two distinct pulse broadening functions (PBFs): PBF₁ is appropriate for a thin screen of scattering material between the Earth and a pulsar, while PBF₂ is appropriate for scattering material uniformly distributed along the line of sight from the Earth to a pulsar. We found that some observations were better fit by PBF₁ and some by PBF₂. Pulse broadening times (\d) are derived from fits of PBFs to the data, and are compared with the predictions of a smoothed model of the Galactic electron distribution. Several lines of sight show excess broadening, which we model as clumps of high density scattering material. A global analysis of all available data finds that the pulse broadening scales with frequency, \, as \ \\^-\ where \\ 3. 9\ 0. 2. This is somewhat shallower than the value \=4. 4 expected from a Kolmogorov medium, but could arise if the spectrum of turbulence has an inner cutoff at \ 300--800 km. A few objects follow particularly shallow scaling laws (the mean scaling index \ \ 3. 1 \ 0. 1 and \ 3. 8 \ 0. 2 respectively for the case of PBF₁ and PBF₂), which may arise from large scale refraction or from the truncation of scattering screens transverse to the Earth--pulsar line of sight.