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标题：Dispersion measure variability for 36 millisecond pulsars at 150 MHz with LOFAR
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作者：J. Y. Donner ; J. P. W. Verbiest ; C. Tiburzi 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2020
卷号：644
页码：1-16
DOI：10.1051/0004-6361/202039517
语种：English
出版社：EDP Sciences
摘要：Context.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 (PTAs) that aim to detect nanohertz gravitational waves.Aims.We aim to quantify the time-variable dispersion with much improved precision and characterise the spectrum of these variations.Methods.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 yr with the LOw Frequency ARray (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.Results.We achieve a median DM precision of the order of 10−5cm−3pc 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 2 × 10−4cm−3pc. The noise contribution to pulsar timing experiments at higher frequencies is calculated to be at a level of 0.1–10μs at 1.4 GHz over a timespan of a few years, which is in many cases larger than the typical timing precision of 1μs 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.Conclusions.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.
关键词：Key wordsengravitational wavespulsars: generalISM: structure