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

Context. Observing Jupiter's synchrotron emission from the Earth remains today the sole method to scrutinize the distribution and dynamical behavior of the ultra energetic electrons magnetically trapped around the planet (because in-situ particle data are limited in the inner magnetosphere). Aims. We perform the first resolved and low-frequency imaging of the synchrotron emission with LOFAR at 127 MHz. The radiation comes from low energy electrons (~1-30 MeV) which map a broad region of Jupiter's inner magnetosphere. Methods (see article for complete abstract) Results. The first resolved images of Jupiter's radiation belts at 127-172 MHz are obtained along with total integrated flux densities. They are compared with previous observations at higher frequencies and show a larger extent of the synchrotron emission source (>=4 RJ). The asymmetry and the dynamic of east-west emission peaks are measured and the presence of a hot spot at lambda_III=230 {\deg} ± 25 {\deg}. Spectral flux density measurements are on the low side of previous (unresolved) ones, suggesting a low-frequency turnover and/or time variations of the emission spectrum. Conclusions. LOFAR is a powerful and flexible planetary imager. The observations at 127 MHz depict an extended emission up to ~4-5 planetary radii. The similarities with high frequency results reinforce the conclusion that: i) the magnetic field morphology primarily shapes the brightness distribution of the emission and ii) the radiating electrons are likely radially and latitudinally distributed inside about 2 RJ. Nonetheless, the larger extent of the brightness combined with the overall lower flux density, yields new information on Jupiter's electron distribution, that may shed light on the origin and mode of transport of these particles.

M. J. Bentum | G. Mann | M. C. Toribio | R. A. M. J. Wijers | G. Bernardi | O. Smirnov | A. Corstanje | H. Falcke | S. Thoudam | J. Anderson | S. Bourdarie | J. N. Girard | J. Swinbank | P. Maat | A. Rowlinson | M. E. Bell | J. Eisloffel | M. Kuniyoshi | P. Zarka | A. Nelles | A. W. Gunst | D. McKay-Bukowski | W. Reich | R. J. van Weeren | J. van Leeuwen | R. P. Breton | A. Asgekar | W. Frieswijk | A. Bonafede | F. de Gasperin | M. Iacobelli | M. Pandey-Pommier | C. Tasse | I. van Bemmel | F. Breitling | W. N. Brouw | M. Bruggen | B. Ciardi | E. de Geus | S. Duscha | J. Horandel | V. I. Kondratiev | M. Loose | R. McFadden | H. Munk | M. J. Norden | H. Paas | A. G. Polatidis | D. Schwarz | C. Vocks | O. Wucknitz | M. Steinmetz | I. de Pater | S. Hess | M. A. Garrett | E. Juette | R. Pizzo | A. Corstanje | H. Falcke | A. Nelles | S. Thoudam | M. Steinmetz | A. Deller | A. Rowlinson | O. Wucknitz | F. Breitling | J. Hessels | J. Leeuwen | I. Pater | P. Zarka | J. Hörandel | S. Corbel | B. Ciardi | S. Hess | O. Smirnov | I. V. Bemmel | G. Bernardi | P. Best | R. Vermeulen | R. Wijers | R. Pizzo | James M. Anderson | A. Bonafede | F. Gasperin | C. Tasse | W. Frieswijk | M. Tagger | S. Markoff | G. Mann | M. Brüggen | M. Garrett | R. Breton | W. Reich | J. Broderick | J. Swinbank | M. Bell | J. Grießmeier | W. Brouw | V. Kondratiev | M. Iacobelli | M. Toribio | M. Norden | R. McFadden | R. V. Weeren | M. Pandey-Pommier | M. Hoeft | S. Bourdarie | A. Asgekar | A. Gunst | M. Kuniyoshi | P. Maat | H. Paas | A. Polatidis | C. Vocks | J. Girard | D. Santos-Costa | G. Kuper | D. Schwarz | S. Duscha | E. Juette | H. Munk | E. Geus | D. McKay-Bukowski | M. Bentum | M. Loose | J. Moldón | J. Eislöffel | P. Best | J. W. T. Hessels | E. Orru | M. Tagger | J. W. Broderick | M. Hoeft | G. Kuper | R. Vermeulen | A. Deller | J. Moldon | Q. Nenon | A. Sicard | S. Corbel | J. Griessmeier | H. Rottgering | D. Santos-Costa | S. Markov | Q. Nénon | A. Sicard | E. Orrú | H. Röttgering | R. Weeren | J. V. Leeuwen | E. D. Geus | J. V. Leeuwen | Q. Nénon

[1]  I. Pater,et al.  An intercomparison of three‐dimensional reconstruction techniques using data and models of Jupiter's synchrotron radiation , 1998 .

[2]  F. Tsuchiya,et al.  Short‐term changes in Jupiter's synchrotron radiation at 325 MHz: Enhanced radial diffusion in Jupiter's radiation belt driven by solar UV/EUV heating , 2011 .

[3]  Sebastien Bourdarie,et al.  A physical model for electron radiation belts of Saturn , 2012 .

[4]  S. Bolton,et al.  Discussing the processes constraining the Jovian synchrotron radio emission's features , 2008 .

[5]  V. Radhakrishnan,et al.  21-Cm Absorption Studies of Galactic Radio Sources , 1960 .

[6]  R. Sault,et al.  Evidence for short-term variability of Jupiter's decimetric emission from VLA observations , 2009 .

[7]  J. Roerdink,et al.  A morphological algorithm for improving radio-frequency interference detection , 2012, 1201.3364.

[8]  Krishan K. Khurana,et al.  Euler potential models of Jupiter's magnetospheric field , 1997 .

[9]  Richard M. Thorne,et al.  Synchrotron emission images from three-dimensional modeling of the Jovian electron radiation belts , 2001 .

[10]  Julien N. Girard,et al.  Sparse representations and convex optimization as tools for LOFAR radio interferometric imaging , 2015, 1504.03896.

[11]  Matthew T. Whiting,et al.  duchamp: a 3D source finder for spectral‐line data , 2012, 1201.2710.

[12]  L. Bruzzone,et al.  Natural radio emission of Jupiter as interferences for radar investigations of the icy satellites of Jupiter , 2011 .

[13]  J. Anderson,et al.  LOFAR sparse image reconstruction , 2014, 1406.7242.

[14]  I. Pater.  A comparison of the radio data and model calculations of Jupiter's synchrotron radiation, 1. The high energy electron distribution in Jupiter's inner magnetosphere , 1981 .

[15]  B. Butler,et al.  VLA observations of synchrotron radiation at 15 GHz , 2008 .

[16]  Thomas R. McDonough,et al.  Jupiter's radiation belts , 1973 .

[17]  J. Roberts,et al.  Polarization and Angular Extent of the 960-Megacycle Radiation from Jupiter. , 1960 .

[18]  Chengcheng Tao,et al.  Effect of solar UV/EUV heating on the intensity and spatial distribution of Jupiter's synchrotron radiation , 2012 .

[19]  Tim J. Cornwell,et al.  The Noncoplanar Baselines Effect in Radio Interferometry: The W-Projection Algorithm , 2008, IEEE Journal of Selected Topics in Signal Processing.

[20]  N. Branson.  High Resolution Radio Observations of the Planet Jupiter , 1968 .

[21]  B. Butler,et al.  Low-frequency VLA observations of jupiter , 2003 .

[22]  A. Lagg,et al.  Long-term dynamics of the inner Jovian electron radiation belts , 2004 .

[23]  D. A. Green,et al.  Jupiter's radio spectrum from 74 MHz up to 8 GHz , 2003 .

[24]  Sebastien Bourdarie,et al.  Physical Electron Belt Model from Jupiter's surface to the orbit of Europa , 2004 .

[25]  Sebastien Bourdarie,et al.  Jupiter's inner radiation belts , 2004 .

[26]  I. Pater.  LOFAR and Jupiter's radio (synchrotron) emissions , 2004 .

[27]  I. Pater,et al.  Synchrotron evidence for Amalthea's influence on Jupiter's electron radiation belt , 1997 .

[28]  I. Pater,et al.  Modification of the Jovian Radiation Belts by Shoemaker–Levy 9: An Explanation of the Data , 2001 .

[29]  I. de Pater,et al.  Jupiter’s Synchrotron Radiation Mapped with the Very Large Array from 1981 to 1998 , 2005 .

[30]  S. Bhatnagar,et al.  Applying full polarization A-Projection to very wide field of view instruments: An imager for LOFAR , 2012, 1212.6178.

[31]  I. Pater,et al.  VLA observations of Jupiter’s synchrotron radiation at 15 and 22 GHz , 2003 .

[32]  D. J. Saikia,et al.  The Low-Frequency Radio Universe , 2009 .

[33]  I. Pater,et al.  Multifrequency analysis of the Jovian electron-belt radiation during the Cassini flyby of Jupiter , 2014 .

[34]  W. Smyth,et al.  An explanation for the east–west asymmetry of the Io plasma torus , 1997 .

[35]  A. Dessler.  Physics of the Jovian Magnetosphere: Coordinate systems , 1983 .

[36]  M. J. Klein,et al.  Correlation studies between solar wind parameters and the decimetric radio emission from Jupiter , 1989 .

[37]  R. Sault,et al.  VLA observations at 6.2 cm of the response of Jupiter's electron belt to the July 2009 event , 2011 .

[38]  C. Heiles,et al.  Outburst of Jupiter's synchrotron radiation after the impact of comet Shoemaker-Levy 9. , 1995, Science.

[39]  Philippe Zarka,et al.  Fast radio imaging of Jupiter's magnetosphere at low-frequencies with LOFAR , 2004 .

[40]  S. Markoff,et al.  LOFAR - low frequency array , 2006 .

[41]  I. Pater,et al.  Observations of Jupiter at 3.5 cm and 6.0 cm Associated with the Impact of Comet P/Shoemaker–Levy 9 , 1998 .

[42]  O. Smirnov,et al.  Radio interferometric gain calibration as a complex optimization problem , 2015, 1502.06974.

[43]  Cyril Tasse,et al.  Applying Wirtinger derivatives to the radio interferometry calibration problem , 2014, 1410.8706.

[44]  M. Hobson,et al.  Radio source calibration for the Very Small Array and other cosmic microwave background instruments at around 30 GHz , 2008 .

[45]  R. G. Conway,et al.  Non-Dipole Terms in the Magnetic Fields of Jupiter and the Earth , 1972 .