Imaging Jupiter's radiation belts down to 127 MHz with LOFAR

Girard JN, Zarka P, Tasse C, Hess S, De Paters I, Santos-Costa D, Nenon Q, Sicard A, Bourdarie S, Anderson J, Asgekar A, Bell ME, Van Bemmel I, Bentum MJ, Bernardi G, Best P, Bonafede A, Breitling F, Breton RP, Broderick JW, Brouw WN, Brueggen M, Ciardi B, Corbel S, Corstanje A, De Gasperin F, De Geus E, Deller A, Duscha S, Eisloffel J, Falcke H, Frieswijk W, Garrett MA, Griessmeier J, Gunst AW, Hessels JWT, Hoeft M, Horandel J, Iacobelli M, Juette E, Kondratiev VI, Kuniyoshi M, Kuper G, Van Leeuwen J, Loose M, Maat P, Mann G, Markoff S, Mcfadden R, Mckay-Bukowski D, Moldon J, Munk H, Nelles A, Norden MJ, Orru E, Paas H, Pandey-Pommier M, Pizzo R, Polatidis AG, Reich W, Roettgering H, Rowlinson A, Schwarz D, Smirnov O, Steinmetz M, Swinbank J, Tagger M, Thoudam S, Toribio MC, Vermeulen R, Vocks C, Van Weeren RJ, Wijers RAMJ, Wucknitz O (2016)

Publication Type: Journal article

Publication year: 2016

Journal

Book Volume: 587

Article Number: A3

DOI: 10.1051/0004-6361/201527518

Abstract

Context.With the limited amount of in situ particle data available for the innermost region of Jupiter's magnetosphere, Earth-based observations of the giant planets synchrotron emission remain the sole method today of scrutinizing the distribution and dynamical behavior of the ultra energetic electrons magnetically trapped around the planet. Radio observations ultimately provide key information about the origin and control parameters of the harsh radiation environment. Aims.We perform the first resolved and low-frequency imaging of the synchrotron emission with LOFAR. At a frequency as low as 127 MHz, the radiation from electrons with energies of 1-30 MeV are expected, for the first time, to be measured and mapped over a broad region of Jupiter's inner magnetosphere. Methods. Measurements consist of interferometric visibilities taken during a single 10-hour rotation of the Jovian system. These visibilities were processed in a custom pipeline developed for planetary observations, combining flagging, calibration, wide-field imaging, direction-dependent calibration, and specific visibility correction for planetary targets. We produced spectral image cubes of Jupiter's radiation belts at the various angular, temporal, and spectral resolutions from which flux densities were measured. Results. The first resolved images of Jupiter's radiation belts at 127-172 MHz are obtained with a noise level ∼20-25 mJy/beam, along with total integrated flux densities. They are compared with previous observations at higher frequencies. A greater extent of the synchrotron emission source (4 RJ) is measured in the LOFAR range, which is the signature-as at higher frequencies-of the superposition of a "pancake" and an isotropic electron distribution. Asymmetry of east-west emission peaks is measured, as well as the longitudinal dependence of the radial distance of the belts, and the presence of a hot spot at λm = 230° ± 25°. Spectral flux density measurements are on the low side of previous (unresolved) ones, suggesting a low-frequency turnover and/or time variations of the Jovian synchrotron spectrum. Conclusions. LOFAR proves to be a powerful and flexible planetary imager. In the case of Jupiter, observations at 127 MHz depict the distribution of ∼1-30 MeV energy electrons up to ∼4-5 planetary radii. The similarities of the observations at 127 MHz with those at higher frequencies reinforce the conclusion that the magnetic field morphology primarily shapes the brightness distribution features of Jupiter's synchrotron emission, as well as how the radiating electrons are likely radially and latitudinally distributed inside about 2 planetary radii. Nonetheless, the detection of an emission region that extends to larger distances than at higher frequencies, combined with the overall lower flux density, yields new information on Jupiter's electron distribution, and this information may ultimately shed light on the origin and mode of transport of these particles.

Authors with CRIS profile

Involved external institutions

Netherlands Institute for Radio Astronomy Netherlands (NL) PSL Research University / Université de recherche Paris Sciences et Lettres France (FR) University of Manchester United Kingdom (GB) Leiden University Netherlands (NL) Max-Planck-Institut für Radioastronomie / Max Planck Institute for Radio Astronomy Germany (DE) Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ Germany (DE) Leibniz Institute for Astrophysics Potsdam / Leibniz-Institut für Astrophysik Potsdam Germany (DE) Ruhr-Universität Bochum (RUB) Germany (DE) Commissariat à l'énergie atomique France (FR) Office National d'Etudes et de Recherches Aérospatiales (ONERA) / The French Aerospace Lab France (FR) University of California, Berkeley United States (USA) (US) Southwest Research Institute (SwRI) United States (USA) (US) Harvard University United States (USA) (US) Universität Hamburg (UHH) Germany (DE) University of Southampton United Kingdom (GB) The Royal Observatory United Kingdom (GB) University of Orléans / Université d'Orléans France (FR) National Astronomical Observatory of Japan / 国立天文台(NAOJ) Japan (JP) University of Amsterdam Netherlands (NL) Oulun Yliopisto / University of Oulo Finland (FI) Universität Bielefeld Germany (DE) Observatoire de Lyon France (FR) Radboud University Nijmegen Netherlands (NL) Australia Telescope National Facility (ATNF) Australia (AU) Thüringer Landessternwarte Tautenburg (TLS) - Karl-Schwarzschild-Observatorium Germany (DE) Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. (MPG) / Max Planck Society for the Advancement of Science Germany (DE) Rhodes University South Africa (ZA) University of Groningen / Rijksuniversiteit Groningen Netherlands (NL)

How to cite

APA:

Girard, J.N., Zarka, P., Tasse, C., Hess, S., De Paters, I., Santos-Costa, D.,... Wucknitz, O. (2016). Imaging Jupiter's radiation belts down to 127 MHz with LOFAR. Astronomy & Astrophysics, 587. https://dx.doi.org/10.1051/0004-6361/201527518

MLA:

Girard, J. N., et al. "Imaging Jupiter's radiation belts down to 127 MHz with LOFAR." Astronomy & Astrophysics 587 (2016).

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