Long-term timing results of ecliptic pulsars observed with I-LOFAR

¹ Physics, School of Natural Sciences & Center for Astronomy, College of Science and Engineering, University of Galway, University Road, Galway H91 TK33, Ireland
² School of Physics, Trinity College Dublin, College Green, Dublin 2, D02 PN40, Ireland
³ Radio Astronomy Laboratory, University of California, Berkeley, CA, USA
⁴ ASTRON, The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁵ Florida Space Institute, University of Central Florida, 12354 Research Parkway, Partnership 1 Building, Suite 214, Orlando, FL 32826-0650, USA
⁶ INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy

^★ Corresponding author

Received: 21 February 2025
Accepted: 13 May 2025

Abstract

Context. Pulsar timing at low frequencies offers a powerful tool for studying the interstellar medium. Additionally, pulsar observations in the ecliptic enable us to study the effects of the solar wind, which becomes much more prominent at low radio frequencies. The Irish station of the LOw Frequency ARray (I-LOFAR) is a sensitive low-frequency radio telescope capable of delivering high-precision data for pulsar studies.

Aims. We present a comprehensive dataset of times of arrival, timing solutions, and dispersion measure (DM) time series for seven ecliptic pulsars observed over two to three years with I-LOFAR. The primary objectives are to investigate time-dependent dispersion effects and provide high-precision timing data for pulsar timing experiments.

Methods. We measured DM variations through pulsar timing and analysed them across different ecliptic latitudes to assess the impact of the solar wind on each pulsar. We modelled the intrinsic pulse-profile variability as a function of frequency.

Results. The high-precision DM time series for all seven pulsars exhibit clear variations that are dependent on their ecliptic latitudes, revealing the impact of the solar wind. Some pulsars show significant changes in their pulse widths across the frequency band, while others remain stable. We examined and quantified the pulse-nulling present in PSR J0826+2637, report evidence of DM chromaticity in PSR J1645-0317, and describe how PSR J2145-0750’s DM precision is such that it could resolve the ionospheric DM contribution. This makes it a target of interest for telescopes in areas of the globe where the ionospheric electron density is higher, for example the Murchison Radio Observatory in Australia.

Conclusions. This data release underscores the potential of I-LOFAR, or any stand-alone international LOFAR station, for advancing low-frequency pulsar studies, particularly in analyses of dispersion in the interstellar medium, the solar wind, and the ionosphere.