Assessing Quasi‐Periodicities in Jovian X‐Ray Emissions: Techniques and Heritage Survey

C. M. Jackman,G. Branduardi‐Raymont,P. Ford,R. Elsner,D. Altamirano,R. Gladstone,C. Knigge,R. Kraft,W. Dunn

doi:10.1029/2018ja025490

Abstract

AbstractJupiter's auroral X‐rays are rather mysterious, with an unknown driver, and several previous reports of individual cases of quasi‐periodic emission. In this work we revisit heritage X‐ray data sets from the 1990s to 2015 and apply robust significance testing of emerging quasi‐periodicities, seeking to understand the robustness and regularity of previously reported quasi‐periodic emissions. Our analysis incorporates the use of the Rayleigh test as an alternative to Lomb‐Scargle analysis or Fast Fourier Transforms, where Rayleigh is particularly suited to a time‐tagged data set of sparse counts such as is common for jovian X‐ray data. Furthermore, the analysis techniques that we present (including Rayleigh testing and Monte Carlo simulation) can be applied to any time‐tagged data set. The code to conduct such analysis is released as supplementary information to accompany this paper. The five most significant (p value <0.01) quasi‐periods from Jupiter's northern auroral region have periods ranging from ~8.0 to 45.96 min, and the two most significant (p value <0.01) quasi‐periods from the south have periods of ~14.1 and ~34.9 min. The selection of a restrictive hot spot source region seems to be critical for detecting quasi‐periodic emission, suggesting that the site of pulsations may be spatially localized. Periods vary from one Jupiter rotation to the next in one long observation, and the north and south are shown to pulse independently in another conjugate observation. These results have important implications for understanding the driver of jovian X‐ray emission.

Highlights

Jupiter’s X-ray emission was first discovered using data from the Einstein observatory (Metzger et al, 1983)
Previous works have reported individual observations of significant quasi-periodic emissions emerging from the jovian system in X-ray, UV, and radio wavelengths
In this paper we have explored Chandra observations of Jupiter’s X-ray emissions from 1999 to 2015, with a focus on the search for statistically significant quasi-periods

Summary

Introduction

Jupiter’s X-ray emission was first discovered using data from the Einstein observatory (Metzger et al, 1983). In more recent years Jupiter’s X-rays have been studied using the Chandra, XMM-Newton, and NuSTAR observatories. The second is the hot spot, generated when ions precipitating into the upper atmosphere produce soft X-ray lines through charge exchange collisions with atmospheric neutral hydrogen molecules (e.g., Cravens et al, 2003; Elsner et al, 2005). A northern polar region hot spot was first discovered by Chandra during the year 2000 Cassini flyby of Jupiter (Gladstone et al, 2002; hereafter G02), and XMM spectral analysis showed that the precipitating ions which cause the hot spot comprise mostly oxygen and carbon/sulfur (e.g., Branduardi-Raymont et al, 2007), albeit with an unknown source. Dunn et al (2017; hereafter D17) reported the discovery of an independent southern auroral X-ray hot spot

Results

Discussion

Conclusion