Pulsars identified in the LOFAR Two-metre Sky Survey at 144 MHz

TL;DR

This paper reports the identification of 80 known radio pulsars in LOFAR Two-metre Sky Survey data at 144 MHz, providing new positions and flux densities, and explores methods for selecting pulsar candidates using polarization and spectral data.

Contribution

The study presents the first large-scale astrometric identification of pulsars in LOFAR data and evaluates candidate selection techniques using polarization and spectral indices.

Findings

80 pulsars identified at 144 MHz in LoTSS DR2

Good agreement between LoTSS flux densities and literature values

Polarization-based candidate selection is highly effective

Abstract

We present the astrometric identification of 80 known radio pulsars as unresolved continuum sources detected at 144 MHz in the second data release of the LOFAR Two-metre Sky Survey (LoTSS DR2), which covers 27% of the Northern hemisphere. These identifications represent the majority ($\geq$ 86%) of radio pulsars present in the LoTSS DR2 footprint and provide independent celestial positions and flux densities at 144 MHz. We compare LoTSS flux densities with literature values from various image and time-domain observations and find good agreement for all but two pulsars. We attribute these flux density deviations to intrinsic pulsar properties (nulling and off-pulse emission). We investigate criteria to select promising pulsar candidates using data from the upcoming LoTSS release of the entire Northern sky ($\delta>0^\circ$), as well as the LOFAR LBA Sky Survey (LoLSS) at 54 MHz (covering $\delta>24^\circ$). Of the 80 detections, 35 (44%) were blindly redetected based on their linear or circular polarization. Therefore we conclude that candidate selection based on polarization properties is a promising approach. Candidate selection can be supplemented with spectral indices via cross-matching to LoLSS sources at 54 MHz, as the high sensitivity of LoTSS is not matched by image-domain surveys at higher frequencies.