Analytical estimate for low-altitude ENA emissivity

We formulate the first analytical model for energetic neutral atom (ENA) emissivity that partially corrects for the global viewing geometry dependence of low-altitude emissions (LAEs) observed by Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS). The emissivity correction requires the pitch angle distribution (PAD) and geophysical location of low-altitude ENAs. To estimate PAD, we create an energy-dependent analytical model, based on a Monte Carlo simulation. We account for energy binning by integrating model PAD over each energy bin. We account for finite angular pixels by computing emissivity as an integral over the pitch angle range sampled by the pixel. We investigate location uncertainty in TWINS pixels by performing nine variations of the emissivity calculation. Using TWINS 2 ENA imaging data from 1131 to 1145 UT on 6 April 2010, we derive emissivity-corrected ion fluxes for two angular pixel sizes: 4° and 1°. To evaluate the method, we compare TWINS-derived ion fluxes to simultaneous in situ data from the National Oceanic and Atmospheric Administration (NOAA) 17 satellite. The TWINS-NOAA agreement for emissivity-corrected flux is improved by up to a factor of 7, compared to uncorrected flux. The highest 1° pixel fluxes are a factor of 2 higher than for 4° pixels, consistent with pixel-derived fluxes that are artificially low because subpixel structures are smoothed out, and indicating a possible slight advantage to oversampling the instrument-measured LAE signal. Both TWINS and NOAA ion fluxes decrease westward of 2000 magnetic local time. The TWINS-NOAA comparison indicates that the global ion precipitation oval comprises multiple smaller-scale (3-5° of latitude) structures.CODYMAV; PRODEX - PROgramme de Développement d'Expériences scientifique

Chandra observations of Jupiter's X-ray auroral emission during Juno apojove 2017

Jupiter's auroral X-rays have been observed for 40 years with an unknown driver producing quasi-periodic emission, concentrated into auroral hot spots. In this study we analyze a ∼ 10 hour Chandra observation from 18:56 on June 18th 2017. We use a new Python pipeline to analyze the auroral morphology; perform timing analysis by incorporating Rayleigh testing and use in situ Juno observations to infer the magnetosphere was compressed during the Chandra interval. During this time Juno was near its apojove position of ∼ 112 RJ, on the dawn flank of the magnetosphere near the nominal magnetopause position. We present new dynamical polar plots showing an extended X-ray hot spot in the northern auroral region traversing across the jovian disk. From this morphology, we propose setting a numerical threshold of > 7 photons per 5° System III longitude × 5° latitude to define a photon concentration of the northern hot spot region. Our timing analysis finds two significant quasi-periodic oscillations (QPOs) of ∼ 37 and ∼ 26 minutes within the extended northern hot spot. No statistically significant QPOs were found in the southern X-ray auroral emission. The Rayleigh test is combined with Monte Carlo simulation to find the statistical significance of any QPOs found. We use a flux equivalence mapping model to trace the possible origin of the QPOs, and thus the driver, to the dayside magnetopause boundary