Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes

C. Sotomayor-Beltran (1) , C. Sobey (2) , J. W. T. Hessels (3) , G. de Bruyn , A. Noutsos (2) , A. Alexov (4) , J. Anderson (2) , A. Asgekar (4) , I. M. Avruch (5) , R. Beck (6) , M. E. Bell , M. R. Bell , M. J. Bentum (4) , G. Bernardi (7) , P. Best (8) , L. Birzan (9) , A. Bonafede (10) , F. Breitling (11) , J. Broderick (12) , W. N. Brouw (13) , M. Brüggen (10) , B. Ciardi (14) , F. de Gasperin (15) , R.-J. Dettmar (1) , A. van Duin , S. Duscha (4) , J. Eislöffel (16) , H. Falcke (4, 2, 17) , R. A. Fallows (18) , R. Fender (12) , C. Ferrari (19) , W. Frieswijk (4) , M. A. Garrett (4, 9) , Jean-Mathias Griessmeier (20, 21) , T. Grit , A. W. Gunst (4) , T. E. Hassall (22) , G. Heald (4) , M. Hoeft (16) , A. Horneffer (14) , M. Iacobelli (9) , E. Juette (23) , A. Karastergiou (24) , E. Keane (25) , J. Kohler (26) , M. Kramer (2) , V. I. Kondratiev (4) , L. V. E. Koopmans (13) , M. Kuniyoshi (2) , G. Kuper (4) , J. van Leeuwen (3) , P. Maat (4) , G. Macario (19) , S. Markoff (27) , J. P. Mckean (4) , D. D. Mulcahy , H. Munk (4) , E. Orru (4) , H. Paas (28) , M. Pandey-Pommier (29) , M. Pilia (4) , R. Pizzo (4) , A. G. Polatidis (4) , W. Reich (2) , H. Röttgering (9) , M. Serylak (21, 20) , J. Sluman (4) , B. W. Stappers (22) , Michel Tagger (21) , Y. Tang (4) , C. Tasse (30) , S. ter Veen (31) , R. Vermeulen (4) , R. J. van Weeren (4) , R. A. M. J. Wijers , S. J. Wijnholds (4) , M. W. Wise (27, 4) , O. Wucknitz (32) , S. Yatawatta (13) , P. Zarka (30)

1 Astronomisches Institut der Ruhr-Universität Bochum
2 MPIFR - Max-Planck-Institut für Radioastronomie
3 UvA - University of Amsterdam [Amsterdam] = Universiteit van Amsterdam
4 ASTRON - Netherlands Institute for Radio Astronomy
5 SRON - SRON Netherlands Institute for Space Research
6 LCPM - Laboratoire de Chimie Physique Moléculaire
7 CfA - Harvard-Smithsonian Center for Astrophysics
8 Edin. - University of Edinburgh
9 Leiden Observatory [Leiden]
10 Jacobs University = Constructor University [Bremen]
11 AIP - Leibniz-Institut für Astrophysik Potsdam
12 University of Southampton
13 Kapteyn Astronomical Institute [Groningen]
14 Max Planck Institute for Astrophysics
15 Hamburger Sternwarte/Hamburg Observatory
16 TLS - Thüringer Landessternwarte Tautenburg
17 Radboud University [Nijmegen]
18 Institute of Mathematical and Physical Sciences
19 LAGRANGE - Joseph Louis LAGRANGE
20 USN - Unité Scientifique de la Station de Nançay
21 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
22 Jodrell Bank Centre for Astrophysics
23 RUB - Ruhr University Bochum = Ruhr-Universität Bochum
24 Oxford Astrophysics
25 Centre for Astrophysics and Supercomputing
26 KIT - Karlsruhe Institute of Technology
27 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
28 Center for Information Technology CIT
29 CRAL - Centre de Recherche Astrophysique de Lyon
30 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
31 IMAPP - Institute for Mathematics, Astrophysics and Particle Physics
32 AlfA - Argelander-Institut für Astronomie

Faraday rotation measurements using the current and next generation of low-frequency radio telescopes will provide a powerful probe of astronomical magnetic fields. However, achieving the full potential of these measurements requires accurate removal of the time-variable ionospheric Faraday rotation contribution. We present ionFR, a code that calculates the amount of ionospheric Faraday rotation for a specific epoch, geographic location, and line-of-sight. ionFR uses a number of publicly available, GPS-derived total electron content maps and the most recent release of the International Geomagnetic Reference Field. We describe applications of this code for the calibration of radio polarimetric observations, and demonstrate the high accuracy of its modeled ionospheric Faraday rotations using LOFAR pulsar observations. These show that we can accurately determine some of the highest-precision pulsar rotation measures ever achieved. Precision rotation measures can be used to monitor rotation measure variations - either intrinsic or due to the changing line-of-sight through the interstellar medium. This calibration is particularly important for nearby sources, where the ionosphere can contribute a significant fraction of the observed rotation measure. We also discuss planned improvements to ionFR, as well as the importance of ionospheric Faraday rotation calibration for the emerging generation of low-frequency radio telescopes, such as the SKA and its pathfinders.

Mots clés: polarization; techniques: polarimetric

Domaines: Planète et Univers [physics]

C. Sotomayor-Beltran, C. Sobey, J. W. T. Hessels, G. de Bruyn, A. Noutsos, et al.. Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes. Astronomy and Astrophysics - A&A, 2013, 552 (A58), 13 p. ⟨10.1051/0004-6361/201220728⟩. ⟨insu-01291256⟩