Multifrequency analysis of the Jovian electron-belt radiation during theCassiniflyby of Jupiter

Abstract

Aims. We examine Very Large Array (VLA) observations of Jupiter to present evidence of fluctuations in the emission produced by the electron belt in January 2001. Investigating the source of fluctuations will provide new opportunities to discuss the scenarios of temporal changes in Jupiter's synchrotron radiation (i.e., the electron belt) in future data analysis and modeling work. Methods. To discuss the electron belt dynamics during the Cassini flyby of Jupiter, we compare the radio measurements from 2−3 January 2001 with VLA observations obtained on 20−21 December 1988, when viewing geometry and array configuration are comparable. All data are scaled to a standard Earth-Jupiter distance of 4.04 AU for comparison purposes. Brightness distribution maps with identical spatial resolutions and cartography of the equatorial radiation are constructed and examined at the wavelengths of ∼21 cm and ∼90 cm. Results. Rotation-averaged maps show that the emission from the equatorial zones of maximum intensity is weaker by ∼5−40%, but the brightness distribution is spatially more extended on 2−3 January 2001, resulting in a total emission at both wavelengths stronger by ∼35%. Between observation periods, the brightness distributions are observed to evolve differently during the planet rotation. Tomographic reconstructions of the equatorial radiation support our conclusion that the electron-belt population was differently distributed around the planet in December 1988 and January 2001. Conclusions. Our analysis of VLA data sets suggests that the spatial distribution of the electron belt on 2−3 January 2001 is different from that usually observed. Our knowledge of solar activity at the time of the Cassini flyby of Jupiter suggests that the emission from the electron radiation belt was responding to external influences, most likely to solar wind structures rather than to solar radio flux, on a timescale of days to a couple of weeks. Combined results from a multisource data analysis -including spacecraft and radio observations -are needed to confirm this relationship.

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

“…This concurs with the samples of insitu particle data collected by Pioneers 10/11 and the Galileo probe/orbiter in the early 1970s and late 1990s and early 2000s, which have showed dense population of electrons with energies of ∼1-30 MeV in Jupiter's inner magnetosphere. This is compatible with VLA observations of Santos-Costa et al (2014) where the radiation zone of Jupiter at P band is observed to be slightly more extended than at L and C bands (quiet state or while varying). As in images at higher frequencies, the intensity distribution in the image reveals a near-equatorial "pancake" distribution Article number, page 5 of 10 Fig.…”

Observations of MeV electrons in Jupiter's innermost radiation belts and polar regions by the Juno radiation monitoring investigation: Perijoves 1 and 3

“…Flux density of synchrotron emission is shown (~21 cm, averaged over 20° of longitude) for context. Synchrotron map projections [after Santos‐Costa et al ., ] are for the central meridian longitude corresponding to the System III West longitude of the spacecraft near the time of the magnetic equator crossing of each flyby (crossing times shown in lower left corners of maps). Magnetic field lines highlighting peak emissions are plotted for L = 1.3, 1.5, 2, 2.25, 2.5, 3 and were calculated using the VIP4 magnetic field model [ Connerney et al ., ].…”

Modelling the environment around five ultracool dwarfs via the radio domain

“…The Jovian decimetric radiation is produced by high-energy electrons in the Jovian radiation belts due to the gyrosynchrotron mechanism (Carr, Desch & Alexander 1983;Zarka 2000); hence we suggest that the quiescent radio emission of ultracool dwarfs may be produced in a similar way, i.e., it may be considered as an "upscaled" version of the Jovian decimetric radiation. According to imaging radio observations (see, e.g., Bolton et al 2002;SantosCosta, Bolton & Sault 2009;Santos-Costa et al 2014;Girard et al 2016), the source of Jovian decimetric radiation has the shape of a torus located in the equatorial plane, with the major radius of about R c ≃ 1.5R J and the minor radius of about r ≃ 0.5R J (i.e., r ≃ R c − R J ). By assuming a similar source geometry for ultracool dwarfs, we estimate the volume of the emission source as…”