2019ApJ...878..130K

We present multi-frequency scatter-broadening evolution of 29 pulsars observed with the LOw Frequency ARray (LOFAR) and Long Wavelength Array (LWA). We conducted new observations using LOFAR Low Band Antennae as well as utilized the archival data from LOFAR and LWA. This study has increased the total of all multi-frequency or wide-band scattering measurements up to a dispersion measure (DM) of 150 pc cm^–3 by 60%. The scatter-broadening timescale (τ_sc) measurements at different frequencies are often combined by scaling them to a common reference frequency of 1 GHz. Using our data, we show that the τ_sc-DM variations are best fitted for reference frequencies close to 200-300 MHz, and scaling to higher or lower frequencies results in significantly more scatter in data. We suggest that this effect might indicate a frequency dependence of the scatter-broadening scaling index (α). However, a selection bias due to our chosen observing frequencies cannot be ruled out with the current data set. Our data did not favor any particular model of the DM-τ_sc relations, and we do not see a statistically significant break at the low-DM range in this relation. The turbulence spectral index (β) is found to be steeper than what is expected from a Kolmogorov spectrum. This indicates that the local ISM turbulence may have a low wavenumber cutoff or the presence of large-scale inhomogeneities in the line of sight to some of the reported pulsars.