Low-frequency Faraday rotation measures towards pulsars using LOFAR: probing the 3D Galactic halo magnetic field

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 t...

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Bibliographic Details
Published in:	Monthly notices of the Royal Astronomical Society 2019-04, Vol.484 (3), p.3646-3664
Main 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
Format:	Article
Language:	eng
Subjects:	Astrophysics Physics Sciences of the Universe
Online Access:	Get full text
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Summary:	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 quadrants i and ii 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.
ISSN:	0035-8711 1365-2966