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

N. D. Ramesh Bhat; James M. Cordes; Fernando Camilo; David J. Nice; Duncan R. Lorimer

doi:10.1086/382680

paper

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

arXiv:astro-ph/0401067 · doi:10.1086/382680

Abstract

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): PBF $_{1}$ is appropriate for a thin screen of scattering material between the Earth and a pulsar, while PBF $_{2}$ 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 PBF $_{1}$ and some by PBF $_{2}$ . Pulse broadening times ( $τ_{d}$ ) 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, $ν$ , as $\taud \proptoν^{-α}$ where $α \sim 3.9 \pm 0.2$ . This is somewhat shallower than the value $α = 4.4$ expected from a Kolmogorov medium, but could arise if the spectrum of turbulence has an inner cutoff at $\sim$ 300--800 km. A few objects follow particularly shallow scaling laws (the mean scaling index $\meanalpha \sim 3.1 \pm 0.1$ and $\sim 3.8 \pm 0.2$ respectively for the case of PBF $_{1}$ and PBF $_{2}$ ), which may arise from large scale refraction or from the truncation of scattering screens transverse to the Earth--pulsar line of sight.

arXiv commentAccepted for publication in the Astrophysical Journal; 32 pages, 11 figures

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

Abstract

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