Low-frequency Faraday rotation measures towards pulsars using LOFAR: probing the 3D Galactic halo magnetic field. Issue 3 (25th January 2019)

• Record Type: Journal Article
• Authors: Sobey, C; Bilous, A V; Grießmeier, J-M; Hessels, J W T; Karastergiou, A; Keane, E F; Kondratiev, V I; Kramer, M; Michilli, D; Noutsos, A; Pilia, M; Polzin, E J; Stappers, B W; Tan, C M; van Leeuwen, J; Verbiest, J P W; Weltevrede, P; Heald, G; Alves, M I R; Carretti, E; Enßlin, T; Haverkorn, M; Iacobelli, M; Reich, W; Van Eck, C
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 484:Issue 3(2019)
• Page Start: 3646
• Page End: 3664
• Publication Date: 2019-01-25
• Subjects: techniques: polarimetric -- pulsars: general -- ISM: magnetic fields -- Galaxy: structure; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz214
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We determined Faraday rotation measures (RMs) towards 137 pulsars in the northern sky, using Low-Frequency Array (LOFAR) observations at 110–190 MHz. This low-frequency RM catalogue, the largest to date, improves the precision of existing RM measurements on average by a factor of 20 – due to the low frequency and wide bandwidth of the data, aided by the RM-synthesis method. We report RMs towards 25 pulsars for the first time. The RMs were corrected for ionospheric Faraday rotation to increase the accuracy of our catalogue to ≈0.1 rad m −2 . The ionospheric RM correction is currently the largest contributor to the measurement uncertainty. In addition, we find that the Faraday dispersion functions towards pulsars are extremely Faraday thin – mostly less than 0.001 rad m −2 . We use these new precise RM measurements (in combination with existing RMs, dispersion measures, and distance estimates) to estimate the scale height of the Galactic halo magnetic field: 2.0 ± 0.3 kpc for Galactic quadrantsi andii above and below the Galactic plane (we also evaluate the scale height for these regions individually). Overall, our initial low-frequency catalogue provides valuable information about the 3D structure of the Galactic magnetic field.