Probing Solar-Wind Structure During Crab Pulsar Conjunctions with Dispersion and Faraday Rotation
Abstract
Observations of the Crab pulsar (PSR B0531+21) during solar conjunction probe plasma structure in the inner solar wind through radio-propagation effects. We analyze dispersion measure (DM) and rotation measure (RM) measurements from the annual conjunctions of 2022-2026, obtained with the Canadian Hydrogen Intensity Mapping Experiment (CHIME). The 2025 DM time series is distinguished from those of the other years by a secondary enhancement on 21 June, about one week after the main conjunction peak. In our scattering-corrected DM measurements, this feature, ΔDM = (3.95 ± 0.20) × 10−3 pc cm−3, is about 20 times the day-to-day DM scatter outside the conjunction window. The RM time series, measured by combining the single pulses of each observation and corrected for the ionospheric contribution, show conjunction excursions of up to ∼ 60 rad m−2 and changes of sign consistent with crossings of heliospheric magnetic-sector boundaries, but no counterpart to the secondary 2025 DM feature or to a similar post-conjunction DM tail in 2026. From the slope of the RM excess against the DM excess we estimate the electron-density-weighted line-of-sight magnetic field; for the sectors with significant slopes, |⟨ B∥ ⟩| is at least ∼ 0.2 to ∼ 10 mG near conjunction, largest in 2025.
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BibTeX
@misc{xiao2026probing,
title = {{Probing Solar-Wind Structure During Crab Pulsar Conjunctions with Dispersion and Faraday Rotation}},
author = {Huiyu Xiao and Daniel Baker and Thierry Serafin Nadeau and Hao Shen and Dongzi Li and Ue-Li Pen},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.06723},
eprint = {2611.06723},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.06723},
}
RIS
TY - UNPB
TI - Probing Solar-Wind Structure During Crab Pulsar Conjunctions with Dispersion and Faraday Rotation
AU - Huiyu Xiao
AU - Daniel Baker
AU - Thierry Serafin Nadeau
AU - Hao Shen
AU - Dongzi Li
AU - Ue-Li Pen
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2611.06723
UR - https://arxiv.org/abs/2611.06723
AB - Observations of the Crab pulsar (PSR B0531+21) during solar conjunction probe plasma structure in the inner solar wind through radio-propagation effects. We analyze dispersion measure (DM) and rotation measure (RM) measurements from the annual conjunctions of 2022-2026, obtained with the Canadian Hydrogen Intensity Mapping Experiment (CHIME). The 2025 DM time series is distinguished from those of the other years by a secondary enhancement on 21 June, about one week after the main conjunction peak. In our scattering-corrected DM measurements, this feature, ΔDM = (3.95 ± 0.20) × 10^−3 pc cm^−3, is about 20 times the day-to-day DM scatter outside the conjunction window. The RM time series, measured by combining the single pulses of each observation and corrected for the ionospheric contribution, show conjunction excursions of up to ∼ 60 rad m^−2 and changes of sign consistent with crossings of heliospheric magnetic-sector boundaries, but no counterpart to the secondary 2025 DM feature or to a similar post-conjunction DM tail in 2026. From the slope of the RM excess against the DM excess we estimate the electron-density-weighted line-of-sight magnetic field; for the sectors with significant slopes, |⟨ B_∥ ⟩| is at least ∼ 0.2 to ∼ 10 mG near conjunction, largest in 2025.
ER -