Wibisono, Affelia D; (2023) Temporal and Spectral Studies of Jupiter's Auroral and Equatorial X-ray Emissions. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Jupiter's X-ray aurorae are amongst the first extra-terrestrial auroral emissions discovered. Electron bremsstrahlung produces hard X-rays while ion charge exchange releases low energy X-rays. It is not yet conclusive whether all these ions are from the solar wind or from within the Jovian magnetosphere. To try resolve this, solar wind and iogenic plasma models were created for this thesis to fit the XMM-Newton X-ray auroral spectra from June 2017 and September 2019. The iogenic model gave best fits for all the spectra presented here, suggesting that the precipitating ions originated from Io’s volcanoes during these observations. The soft X-rays also occasionally pulse with periods of 8-45 minutes. The June 2017 observation showed that the emissions from both poles shared the same 23–27-minute periodicity for over 12.5 hours, hinting that a global process might be responsible for these pulsations. The planet’s hard X-ray, far- and extreme ultraviolet northern aurorae all brightened simultaneously when dawn storms and injection events appeared in September 2019. Spectral fits suggest that multiple sources of electrons may have precipitated during these instances. The soft X-rays did not follow the same trend, indicating that mechanisms in the inner magnetosphere responsible for the electron precipitation can happen independently to those in the outer magnetosphere that cause the ion precipitation. Jupiter’s atmosphere elastically scatters solar X-rays, and this thesis shows that the planet’s equatorial emissions between 2003-2021 brighten and dim with the solar cycle. The spectra from XMM-Newton’s Reflection Grating Spectrometer instrument of Jupiter’s entire disc display variety between observations and between the different phases of the solar cycle, with line emission being most evident when solar activity is strong. Several future projects have been inspired by the work in this thesis and have already led to procuring X-ray data from approved guest observations with XMM-Newton.

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