2019ApJ...875..146B

Interstellar scattering causes pulsar profiles to grow asymmetrically, thus affecting the pulsar timing residuals, and is strongest at lower frequencies. Different interstellar medium models predict different frequency (ν) and dispersion measure (DM) dependencies for the scattering timescale τ_sc. For Gaussian inhomogeneity the expected scaling relation is τ_sc∝ν^–4 DM², while for a Kolmogorov distribution of irregularities, the expected relation is τ_sc∝ν^–4.4 DM^2.2. Previous scattering studies showed a wide range of scattering index across all ranges of DM. A scattering index below 4 is believed to be either due to limitations of the underlying assumptions of the thin-screen model or an anisotropic scattering mechanism. We present a study of scattering for seven nearby pulsars (DM < 50 pc cm^–3) observed at low frequencies (10-88 MHz), using the first station of the Long Wavelength Array. We examine the scattering spectral index and DM variation over a period of about three years. The results yield insights into the small-scale structure of the interstellar medium, as well as the applicability of the thin-screen model for low-DM pulsars.