Jupiter's X-Ray and UV Dark Polar Region

Abstract

We present 14 simultaneous Chandra X-ray Observatory (CXO)-Hubble Space Telescope (HST) observations of Jupiter's Northern X-ray and ultraviolet (UV) aurorae from 2016 to 2019. Despite the variety of dynamic UV and X-ray auroral structures, one region is conspicuous by its persistent absence of emission: the dark polar region (DPR). Previous HST observations have shown that very little UV emission is produced by the DPR. We find that the DPR also produces very few X-ray photons. For all 14 observations, the low level of X-ray emission from the DPR is consistent (within 2-standard deviations) with scattered solar emission and/or photons spread by Chandra's Point Spread Function from known X-ray-bright regions. We therefore conclude that for these 14 observations the DPR produced no statistically significant detectable X-ray signature.

Keywords: Chandra X‐ray Observatory; Hubble Space Telescope; Jupiter; aurora; dark polar region; magnetosphere.

Figure 1

Overlaid simultaneous UV (blue‐white‐red color map) and X‐ray photon (white dots) longitude‐latitude maps of Jupiter's North Pole, from the Hubble Space Telescope (HST) and Chandra X‐ray Observatory High Resolution Camera (CXO‐HRC). Dates and times of the observations (UT) are at the top of each panel. Only UV and X‐ray emissions produced during this time window are shown. The top left panel highlights different aurora regions, as discussed in the introduction. The main emission is labeled by white arrows, the dark polar region (DPR) is shown in yellow, the Swirl region is shown in pink and the Active Regions (sometimes split into a noon and dusk active region) are shown in Green. The boundary between the active region and swirl region (here labeled with a white “B”) sometimes includes an arc of UV emission, as is the case for the two different observations shown in the top two panels here. The other panels highlight three different UV aurora families, as indicated by the white label in the lower left corner of each. The white shape overlaid onto each map is consistent across each, and highlights the changing spatial distribution of X‐rays for each. For each panel, the location and extent of the DPR are indicated with yellow arrows, showcasing its changing extent from observation‐to‐observation. We note that due to the viewing geometry from Earth and the tilt of Jupiter's pole, visibility of the most poleward latitudes is limited. For consistency, we cutoff the latitude on the maps at 170°.

Figure 2

Overlaid simultaneous UV (blue‐white‐red color map) and X‐ray photon (white dots) longitude‐latitude maps of Jupiter's North Pole, from the Hubble Space Telescope (HST) and Chandra X‐ray Observatory High Resolution Camera (CXO‐HRC). Dates and times of the observations (UT) are at the top of each panel. Only UV and X‐ray emission produced during these times is shown. Panel (a) shows a yellow circle indicating the location of the dark polar region (DPR). Panels (b and i) show white quadrilaterals around example X‐ray photons. The vertices of a given quadrilateral are the extremes of the photon's possible projected longitude‐latitude location based on the projected 1‐sigma (0.4″) point spread function of CXO. See Table 1 for the CML range and Jupiter‐Earth distance for each observation.

Figure 3

UV Observations and X‐ray Observations and Simulations from 19 May 2017. (a) shows an overlaid longitude‐latitude map of UV brightness (color‐map) and X‐ray photons (white dots) and their respective 1‐sigma uncertainty quadrilaterals (white lines around each dot) from Jupiter's Northern aurora on 19 May 2017 from 05:06 to 05:47. The yellow shaded region indicates the DPR at this time as defined from the UV observations, while the purple region shows Region X defined to combine X‐ray emissions observed from the active and swirl region, with 1‐sigma uncertainties that could enable instrument scattering of the photons into the DPR. (b) shows simulated X‐ray emission from within the purple region in (a), as outlined in the main text. (c) applies Chandra's point spread function to the emission in (b) to apply the spatial response of the instrument to such emission. (d) shows the resulting histogram from 100,000 simulations of the X‐ray emission and PSF, showing the number of photons initially produced in the purple region that would be detected in the DPR. (e) shows the Northern hemisphere X‐ray map from the entire 10‐hr observation of Jupiter by Chandra HRC‐I on 19 May 2017. Yellow regions show shifted DPR regions within which the number of photons was measured to quantify scattered solar X‐ray contributions within the DPR. (f) shows the resulting histogram of the number of X‐ray counts scaled for the ratio between the duration of the Chandra observation and the HST observation, to quantify how many scattered solar photons may contribute to the observed DPR emission within the simultaneous CXO‐HST time window. $\mu$ indicates the mean and $\sigma$ the standard deviation for the distribution.