A long-term spectro-temporal study of Jovian X-ray and Ultraviolet response to solar activity

Abstract

We present results from a multi-decade investigation of solar activity-driven variability in Jupiter's emissions, using solar X-ray flux and sunspot numbers as activity indicators and ultraviolet (UV) and X-ray observations from the International Ultraviolet Explorer (IUE; 1978-1996) and the Chandra X-ray Observatory (2011-2021). Analysis of 51 high-SNR UV spectra spanning two solar cycles shows that Jupiter's Ly$\alpha$ emission contains narrow and broad components, likely associated with the disk and auroral regions, respectively. The Ly$\alpha$ line and the 1330-1400 Angstrom continuum flux closely follow variations in solar X-ray flux and sunspot numbers throughout all phases of two consecutive solar cycles, indicating a direct connection with solar irradiation processes, including resonant scattering of solar Ly$\alpha$ photons and photoelectron-driven atmospheric excitation. In contrast, ionised UV lines such as Fe II (1608 Angstrom and 1575 Angstrom) show no correlation with solar activity over a solar cycle, suggesting an internal or magnetospheric origin, potentially linked to Io-derived charged particles or UV/X-ray radiation. To determine whether Jupiter's X-ray response resembles its UV response to solar activity, we analysed 29 Chandra/HRC observations obtained during 2014-2021 and two Chandra/ACIS observations from 2011. Significant X-ray flares are detected in both ACIS and HRC lightcurves 7-15 days after major reported coronal mass ejections (CMEs). Post-CME ACIS auroral spectra reveal a significant ($\geq 3\sigma$) Ne$^{8+}$ emission feature ($\sim$0.94-0.98 keV) near 70-80$^\circ$ latitude at Jupiter's north pole. Owing to the high ionisation energy required ($\sim$1.19 keV for the Ne VIII to Ne IX bound-bound transition), this feature is unlikely to arise from local interactions, supporting CME-driven auroral excitation on Jupiter.