A LOFAR census of non-recycled pulsars: average profiles, dispersion measures, flux densities, and spectra

TL;DR

This LOFAR pulsar census provides detailed low-frequency observations of nearly all known non-recycled pulsars above certain declination and galactic latitude thresholds, offering improved dispersion measures, flux densities, and broadband spectra analysis.

Contribution

It presents the first comprehensive low-frequency survey of non-recycled pulsars, including new spectral fits and high-precision dispersion measures, expanding the understanding of pulsar radio spectra.

Findings

Median dispersion measure uncertainty is ten times smaller than previous catalogues.

First-time broadband spectral fits for 48 pulsars, revealing spectral breaks and turnovers.

Observed significant variability in spectral indices, highlighting uncertainties in previous measurements.

Abstract

We present first results from a LOFAR census of non-recycled pulsars. The census includes almost all such pulsars known (194 sources) at declinations ${\rm Dec}> 8^\circ$ and Galactic latitudes $|{\rm Gb}| > 3^\circ$, regardless of their expected flux densities and scattering times. Each pulsar was observed for $\geq 20$ minutes in the contiguous frequency range of 110--188 MHz. Full-Stokes data were recorded. We present the dispersion measures, flux densities, and calibrated total intensity profiles for the 158 pulsars detected in the sample. The median uncertainty in census dispersion measures ($1.5 \times 10^{-3}$ pc cm$^{-3}$) is ten times smaller, on average, than in the ATNF pulsar catalogue. We combined census flux densities with those in the literature and fitted the resulting broadband spectra with single or broken power-law functions. For 48 census pulsars such fits are being published for the first time. Typically, the choice between single and broken power-laws, as well as the location of the spectral break, were highly influenced by the spectral coverage of the available flux density measurements. In particular, the inclusion of measurements below 100 MHz appears essential for investigating the low-frequency turnover in the spectra for most of the census pulsars. For several pulsars, we compared the spectral indices from different works and found the typical spread of values to be within 0.5--1.5, suggesting a prevailing underestimation of spectral index errors in the literature. The census observations yielded some unexpected individual source results, as we describe in the paper. Lastly, we will provide this unique sample of wide-band, low-frequency pulse profiles via the European Pulsar Network Database.