부산대학교 도서관

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 fitted by PBF1 and some by PBF2. Pulse-broadening times (td) 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, n, as td [?] n-a, where a ~ 3.9 +- 0.2. This is somewhat shallower than the value a = 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 [?]a[?] ~ 3.1 +- 0.1 and ~3.8 +- 0.2, respectively, for 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.