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Les émissions radio aurorales de Jupiter : observations à distance, in-situ, et simulations.

Abstract : The thesis focused on the study of Jupiter's auroral radio emissions, produced close to the local electronic cyclotron frequency by Maser Cyclotron instability, powered by resonant electrons of energies of a few keV, accelerated along high magnetic field lines at high latitude.I first took over, validated and extended the simulation code ExPRES (Exoplanetary and Planetary Radio Emissions Simulator) developed at LESIA, which allows to produce dynamic spectra of visible radio emissions for a given observer. I performed a parametric study of simulations of radio emissions induced by Io in order to quantify the role of the main free parameters of the code (distribution function and energy of the electrons, magnetic field model, position of the active magnetic field line and altitude of the ionospheric cutoff). This study confirmed that Io emissions are correctly reproduced only when the radiation is oblique to the magnetic field lines, which is simulated by ExPRES through loss cone electronic distribution functions. I have also shown that (a) the parameters that mainly control the shape of the simulated emissions in the time-frequency plane are the magnetic field model and the electron energy, and that (b) the simulations are in excellent agreement with observations, with a time window of uncertainty of ± 2 hours.Using this code, I produced long-term simulations of radio emissions induced by Io, and those expected for Europa, Ganymede and Callisto. Comparing these simulations with several years of Jupiter observations recorded with the Voyager / PRA and Cassini / RPWS instruments (punctually supplemented by those of the Nançay decametric array), I proved the existence of radio emissions induced by Europa and Ganymede. The statistical study of these emissions allowed me to establish their average properties (extension in frequency, temporal variability, and occurrence). This result opens a new field of study, remotely and in the long-term, of the planet-satellite interactions other than Io-Jupiter.The comparison of these simulations with the Juno / Waves observations allowed me to unambiguously identify the radio emissions induced by Io, as well as their hemisphere of origin (without knowing their polarization, not measured by Juno / Waves), for an observer close to the equator (case of the Earth), as at higher latitudes. Thanks to these simulations, I have also shown that the emissions are visible only if the opening of the emission angle is greater than 70 ° ± 5 °.Finally, I began a statistical study of the spatial distribution of auroral radio sources traversed by the Juno probe. I thus mapped the sources of the various components (kilometer to HF) of Jovian radio broadcasts. Comparison with recent magnetic field models, as well as UV imagery (Juno / UVS and Hubble / STIS) allowed me to demonstrate a correlation of radio emissions with the main auroral oval.
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Corentin Louis. Les émissions radio aurorales de Jupiter : observations à distance, in-situ, et simulations.. Astrophysique [astro-ph]. Université Paris sciences et lettres, 2018. Français. ⟨NNT : 2018PSLEO023⟩. ⟨tel-02132920⟩

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