Characteristics of Jupiter's X-ray auroral hot spot emissions using Chandra

Abstract:

We present an extensive statistical study of all 29 Chandra High Resolution Camera (HRC-I) observations of the jovian X-ray emissions, covering ~ 20 years worth of data from 18th December 2000 to 8th September 2019. Eight of these observations were pre-Juno and 21 while Juno was exploring the Jovian system providing in situ context. In this study, we characterise the typical and extreme behaviour of the X-ray auroral emissions across the entire catalogue for the first time. In particular, we focus on the X-ray auroral "hot spot". Examining both types of behaviour allows us to determine the full extent of hot spot variability. We focus on the northern hot spot (NHS) as: (1) the viewing geometry over the catalogue favours the North Pole best and (2) the NHS has been shown to be mostly non-conjugate with the south, producing much stronger emission. In this new statistical study, we aim to find the variable X-ray driver by identifying the characteristics of the emissions and find, within errors, where they map to within the jovian system. We present heat maps and 2-D histograms to show the overall average hot spot morphology for the very first time using a numerical criterion of location and photon concentration to define the hot spot emissions (S3 longitude: 100° - 240°; latitude: 40° - 90°; concentration: > 7 photons per 5° S3 lon × 5° lat). From the catalogue, 26 out of 29 observations had emissions within this threshold. We find a significant region of concentrated NHS emission at ~ 162° - 171° S3 longitude and 60° - 66° latitude, herein referred to as the averaged hot spot nucleus (AHSNuc). The AHSNuc is found to mainly map to the noon magnetopause boundary while most events from the NHS are found to originate on the pre-dusk to pre-midnight boundary, suggesting that multiple drivers may produce the emissions. Finally, we apply the Rayleigh test technique to find any significant quasi-periodic oscillations (QPOs) within the hot spot and the AHSNuc. We create a catalogue of all our timing analysis results noting all the significant QPOs found and test their robustness using a Jackknife test. Our mapping and timing analysis suggest that the source of the X-ray emissions may originate from driver/drivers that are linked to ultra-low frequency wave activity on the magnetopause boundary (such as Kelvin-Helmholtz instabilities).