Dispersion measure variability for 36 millisecond pulsars at 150MHz with LOFAR

Abstract

Radio pulses from pulsars are affected by plasma dispersion, which results in a frequency-dependent propagation delay. Variations in the magnitude of this effect lead to an additional source of red noise in pulsar timing experiments, including pulsar timing arrays that aim to detect nanohertz gravitational waves. We aim to quantify the time-variable dispersion with much improved precision and characterise the spectrum of these variations. We use the pulsar timing technique to obtain highly precise dispersion measure (DM) time series. Our dataset consists of observations of 36 millisecond pulsars, which were observed for up to 7.1 years with the LOFAR telescope at a centre frequency of ~150 MHz. Seventeen of these sources were observed with a weekly cadence, while the rest were observed at monthly cadence. We achieve a median DM precision of the order of 10^-5 cm^-3 pc for a significant fraction of our sources. We detect significant variations of the DM in all pulsars with a median DM uncertainty of less than 2x10^-4 cm^-3 pc. The noise contribution to pulsar timing experiments at higher frequencies is calculated to be at a level of 0.1-10 us at 1.4 GHz over a timespan of a few years, which is in many cases larger than the typical timing precision of 1 us or better that PTAs aim for. We found no evidence for a dependence of DM on radio frequency for any of the sources in our sample. The DM time series we obtained using LOFAR could in principle be used to correct higher-frequency data for the variations of the dispersive delay. However, there is currently the practical restriction that pulsars tend to provide either highly precise times of arrival (ToAs) at 1.4 GHz or a high DM precision at low frequencies, but not both, due to spectral properties. Combining the higher-frequency ToAs with those from LOFAR to measure the infinite-frequency ToA and DM would improve the result.

16 pages, 8 figures, 2 tables

References in corpus (9)

• TEMPO2, a new pulsar timing package. I: Overview
• PSRCHIVE and PSRFITS An Open Approach to Radio Pulsar Data Storage and Analysis
• Dispersion Measure Variations and their Effect on Precision Pulsar Timing
• The LOFAR Tied-Array All-Sky Survey (LOTAAS): Survey overview and initial pulsar discoveries
• Pulsar polarisation below 200 MHz: Average profiles and propagation effects
• Model-based asymptotically optimal dispersion measure correction for pulsar timing
• First detection of frequency-dependent, time-variable dispersion measures
• On the usefulness of existing Solar-wind models for pulsar timing corrections
• Pulsar Timing Errors from Asynchronous Multi-Frequency Sampling of Dispersion Measure Variations

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