Fast radio imaging of Jupiter's magnetosphere at low-frequencies with LOFAR

Jupiter emits intense decameter (DAM) radio waves, detectable from the ground in the range similar to10-40 MHz. They are produced by energetic electron precipitations in its auroral regions (auroral-DAM), as well as near the magnetic footprints of the Galilean satellite Io (Io-DAM). Radio imaging of these decameter emissions with arcsecond angular resolution and millisecond time resolution should provide: (1) an improved mapping of the surface planetary magnetic field, via imaging of instantaneous cyclotron sources of highest frequency; (2) measurements of the beaming angle of the radiation relative to the local magnetic field, as a function of frequency; (3) detailed information on the Io-Jupiter electrodynamic interaction, in particular the lead angle between the Io flux tube and the radio emitting field line; (4) direct information on the origin of the sporadic drifting decameter S-bursts, thought to be electron bunches propagating along magnetic field lines, and possibly revealing electric potential drops along these field lines; (5) direct observation of DAM emission possibly related to the Ganymede-Jupiter, Europa Jupiter and/or Callisto-Jupiter interactions, and their energetics; (6) information on the magnetospheric dynamics, via correlation of radio images with ultraviolet and infrared images of the aurora as well as of the Galilean satellite footprints, and study of their temporal variations; (7) an improved mapping of the Jovian plasma environment (especially the Io torus) via the propagation effects that it induces on the radio waves propagating through it (Faraday rotation, diffraction fringes, etc.); (8) possibly on the long-term a better accuracy on the determination of Jupiter's rotation period. Fast imaging should be permitted by the very high intensity of Jovian decameter bursts. LOFAR's capability to measure the full polarization of the incoming waves will be exploited. The main limitation will come from the maximum angular resolution reachable. We discuss several approaches for bringing it close to the value of similar to1 at 30-40 MHz, as required for the above studies. (C) 2004 Elsevier Ltd. All rights reserved.