# Multi-frequency scatter broadening evolution of pulsars - II. Scatter broadening of nearby pulsars

## TL;DR

This study analyzes the scatter broadening of 29 nearby pulsars across multiple frequencies, revealing frequency-dependent effects and suggesting deviations from standard turbulence models in the interstellar medium.

## Contribution

It provides new multi-frequency measurements of scatter broadening for pulsars up to DM 150 pc/cm³, highlighting the importance of reference frequency choice and turbulence spectral index variations.

## Key findings

- Scatter broadening timescales best scaled at 200-300 MHz
- No significant break in DM–τ_sc relation at low DM
- Turbulence spectral index is steeper than Kolmogorov expectation

## Abstract

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 (LBA) 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 ($\tau_{sc}$) 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 $\tau_{sc}$--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 ($\alpha$). However, a selection bias due to our chosen observing frequencies can not be ruled out with the current data set. Our data did not favour any particular model of the DM -- $\tau_{sc}$ relations, and we do not see a statistically significant break at the low DM range in this relation. The turbulence spectral index ($\beta$) is found to be steeper than that is expected from a Kolmogorov spectrum. This indicates that the local ISM turbulence may have a low wave-number cutoff or presence of large scale inhomogeneities in the line of sight to some of the reported pulsars.