Determining the beaming of Io decametric emissions : a remote diagnostic to probe the Io‐Jupiter interaction

L. Lamy (1, 2, 3) , L. Colomban (4) , P. Zarka (2, 1) , R. Prangé (1) , M. Marques , C. Louis , W. Kurth , B. Cecconi (1, 2) , J. Girard (1, 2) , J.-M. Griessmeier (4, 2) , S. Yerin

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics
2 USN - Unité Scientifique de la Station de Nançay
3 LAM - Laboratoire d'Astrophysique de Marseille
4 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace

We investigate the beaming of 11 Io-Jupiter decametric (Io-DAM) emissions observed by Juno/Waves, the Nançay Decameter Array and NenuFAR. Using an up-to-date magnetic field model and three methods to position the active Io Flux Tube (IFT), we accurately locate the radiosources and determine their emission angle θ from the local magnetic field vector. These methods use (i) updated models of the IFT equatorial lead angle, (ii) ultraviolet (UV) images of Jupiter’s aurorae and (iii) multi-point radio measurements. The kinetic energy Ee− of source electrons is then inferred from θ in the framework of the Cyclotron Maser Instability. The precise position of the active IFT achieved from methods (ii,iii) can be used to test the effective torus plasma density. Simultaneous radio/UV observations reveal that multiple Io-DAM arcs are associated with multiple UV spots and provide the first direct evidence of an Io-DAM arc associated with a trans-hemispheric beam UV spot. Multi-point radio observations probe the Io-DAM sources at various altitudes, times and hemispheres. Overall, θ varies a function of frequency (altitude), by decreasing from 75° − 80° to 70° − 75° over 10 − 40 MHz with slightly larger values in the northern hemisphere, and independently varies as a function of time (or longitude of Io). Its uncertainty of a few degrees is dominated by the error on the longitude of the active IFT. The inferred values of Ee− also vary as a function of altitude and time. For the 11 investigated cases, they range from 3 to 16 keV, with a 6.6 ± 2.7 keV average.

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

L. Lamy, L. Colomban, P. Zarka, R. Prangé, M. Marques, et al.. Determining the beaming of Io decametric emissions : a remote diagnostic to probe the Io‐Jupiter interaction. Journal of Geophysical Research Space Physics, In press, ⟨10.1029/2021JA030160⟩. ⟨insu-03619258⟩