We compare Chandra and XMM‐Newton X‐ray observations of Jupiter during 2007 with a rich multi‐instrument data set including upstream in situ solar wind measurements from the New Horizons spacecraft, ...radio emissions from the Nançay Decametric Array and Wind/Waves, and ultraviolet (UV) observations from the Hubble Space Telescope. New Horizons data revealed two corotating interaction regions (CIRs) impacted Jupiter during these observations. Non‐Io decametric bursts and UV emissions brightened together and varied in phase with the CIRs. We characterize three types of X‐ray aurorae: hard X‐ray bremsstrahlung main emission, pulsed/flared soft X‐ray emissions, and a newly identified dim flickering (varying on short time scales, but quasi‐continuously present) aurora. For most observations, the X‐ray aurorae were dominated by pulsed/flaring emissions, with ion spectral lines that were best fit by iogenic plasma. However, the brightest X‐ray aurora was coincident with a magnetosphere expansion. For this observation, the aurorae were produced by both flickering emission and erratic pulses/flares. Auroral spectral models for this observation required the addition of solar wind ions to attain good fits, suggesting solar wind entry into the outer magnetosphere or directly into the pole for this particularly bright observation. X‐ray bremsstrahlung from high energy electrons was only bright for one observation, which was during a forward shock. This bremsstrahlung was spatially coincident with bright UV main emission (power > 1 TW) and X‐ray ion spectral line dusk emission, suggesting closening of upward and downward current systems during the shock. Otherwise, the bremsstrahlung was dim, and UV main emission power was also lower (<700 GW), suggesting their power scaled together.
Key Points
We characterize three types of X‐ray aurorae (main oval, ir/regular pulses, and flickering aurorae) and compare with radio, UV, and solar wind data
Non‐Io decametric bursts occurred with UV auroral brightening, and UV and hard X‐ray main auroral emission also brightened contemporaneously
Soft X‐ray aurora was best fit by iogenic (S, O) spectral lines except during magnetospheric expansion when solar wind ion lines were needed
Abstract Regular and moderate exercise has been considered an interesting neuroprotective strategy. Although the mechanisms by which physical exercise alters brain function are not clear, it appears ...that neuroprotective properties of exercise could be related to chromatin remodeling, specifically the induction of histone acetylation through modulation of histone deacetylases (HDAC) and histone acetyltransferases (HAT) activities. The aim of the present work was to investigate the effect of exercise on HDAC and HAT activities in rat whole hippocampus at different times after treadmill. Adult male Wistar rats were assigned to non-exercised (sedentary) and exercised groups on different protocols: a single session of treadmill exercise (running for 20 min) and a chronic treadmill protocol (running once daily for 20 min, for 2 weeks). The effects of exercise on HDAC and HAT activities were measured immediately, 1 h and 18 h after the single session or the last training session of chronic treadmill exercise using specific assay kits. The single session of treadmill exercise reduced HDAC activity, increased HAT activity and increased the HAT/HDAC balance in rat hippocampus immediately and 1 h after exercise, an indicative of histone hyperacetylation status. The acetylation balance was also influenced by the circadian rhythm, since the HAT/HDAC ratio was significantly decreased in the early morning in all groups when compared to the afternoon. These data support the hypothesis that exercise neuroprotective effects may be related, at least in part, to acetylation levels through modulation of HAT and HDAC activities. We also demonstrated circadian changes in the HAT and HDAC activities and, consequently, in the acetylation levels.
In this study, we evaluated the effects of autologous serum collected after two types of exercise on the in vitro inflammatory profile and T cell phenotype of resting peripheral blood mononuclear ...cells (PBMCs) in obese men. Serum samples and PBMCs were obtained from eight obese men who performed two exercise bouts-high intensity interval exercise (HIIE) and exhaustive exercise session to voluntary fatigue-in a randomized cross-over trial. Pre-exercise PBMCs were incubated with 50% autologous serum (collected before and after each exercise bout) for 4 h. In vitro experiments revealed that post-HIIE serum reduced the histone H4 acetylation status and NF-κB content of PBMCs and suppressed the production of both TNF-α and IL-6 by PBMCs, while increasing IL-10 production. Post-exhaustive exercise serum induced histone H4 hyperacetylation and mitochondrial depolarization in lymphocytes and increased TNF-α production. In vitro post-HIIE serum incubation resulted in an increase in the frequencies of CD4 + CTLA-4 + and CD4 + CD25+ T cells expressing CD39 and CD73. Post-exhaustive exercise serum decreased the frequency of CD4 + CD25 + CD73+ T cells but increased CD4 + CD25-CD39 + T cell frequency. Both post-exercise serums increased the proportions of CD4 + PD-1 + and CD8 + PD-1+ T cells. Blood serum factors released during exercise altered the immune response and T cell phenotype. The type of exercise impacted the immunomodulatory activity of the post-exercise serum on PBMCs.
Jupiter'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.
Key Points
Timing analysis of Chandra observations of Jupiter's X‐ray auroras from 1999 to 2015
Statistically significant quasi‐periodicities in jovian auroral X‐rays are relatively rare and periods variable, even on successive planetary rotations
We use Rayleigh testing and Monte Carlo simulation to search for statistically significant quasi‐periods in sparse, time‐tagged data
We analyze archival Chandra X-ray Observatory observations of Jupiter to search for emission from the Galilean moons. X-ray emission has previously been reported from Io and Europa using a subset of ...these data. We confirm this detection, and marginally detect X-ray emission from both Ganymede and Callisto as well. The X-ray spectrum of Europa is strongly peaked around the neutral oxygen fluorescence line (525 eV), while Io's has peaks at both oxygen and sulfur (2308 eV) plus a broad continuum between 350 and 5000 eV. Ganymede's spectrum is similar to Io's, but without the sulfur peak. A few events, mostly clustered around the oxygen line, are detected from Callisto. Using measurements by the Galileo mission of the specific intensity of ambient protons and electrons, we model the X-ray spectra and flux of the moons from two processes: particle-induced X-ray emission (PIXE) from the impact of energetic protons and X-ray emission from electron bremsstrahlung. With uncertainties of a factor of a few, the electron bremsstrahlung and PIXE models overestimate the X-ray flux from Europa, preventing us from making a definitive statement about the origin of the X-ray emission. The PIXE model of Io predicts emission lines at O and S similar to those observed, but underestimates their flux by nearly two orders of magnitude. Based on this discrepancy in the PIXE flux, combined with the detected broadband continuum in the spectrum, we conclude that the X-ray emission from Io is due to electron bremsstrahlung. Likewise, because of Ganymede's broad continuum, we tentatively conclude that its X-ray emission is also due to electron bremsstrahlung. Callisto is too faint in the X-rays to draw any conclusion. Obtaining in situ X-ray observations of the moons would provide a direct measurement of their elemental composition.
Jupiter's X‐ray Emission During the 2007 Solar Minimum Dunn, W. R.; Branduardi‐Raymont, G.; Carter‐Cortez, V. ...
Journal of geophysical research. Space physics,
June 2020, 2020-06-00, 20200601, Letnik:
125, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The 2007–2009 solar minimum was the longest of the space age. We present the first of two companion papers on Chandra and XMM‐Newton X‐ray campaigns of Jupiter through February–March 2007. We find ...that low solar X‐ray flux during solar minimum causes Jupiter's equatorial regions to be exceptionally X‐ray dim (0.21 GW at minimum; 0.76 GW at maximum). While the Jovian equatorial emission varies with solar cycle, the aurorae have comparably bright intervals at solar minimum and maximum. We apply atomic charge exchange models to auroral spectra and find that iogenic plasma of sulphur and oxygen ions provides excellent fits for XMM‐Newton observations. The fitted spectral S:O ratios of 0.4–1.3 are in good agreement with in situ magnetospheric S:O measurements of 0.3–1.5, suggesting that the ions that produce Jupiter's X‐ray aurora predominantly originate inside the magnetosphere. The aurorae were particularly bright on 24–25 February and 8–9 March, but these two observations exhibit very different spatial, spectral, and temporal behavior; 24–25 February was the only observation in this campaign with significant hard X‐ray bremsstrahlung from precipitating electrons, suggesting this may be rare. For 8–9 March, a bremsstrahlung component was absent, but bright oxygen O6+ lines and best‐fit models containing carbon, point to contributions from solar wind ions. This contribution is absent in the other observations. Comparing simultaneous Chandra ACIS and XMM‐Newton EPIC spectra showed that ACIS systematically underreported 0.45‐ to 0.6‐keV Jovian emission, suggesting quenching may be less important for Jupiter's atmosphere than previously thought. We therefore recommend XMM‐Newton for spectral analyses and quantifying opacity/quenching effects.
Key Points
Jupiter's equatorial X‐ray emission varies in accordance with solar cycle 24 but auroral power can be comparably bright at solar min and max
Charge exchange models provide good fits to aurora spectra retrieving S:O ratios of 0.4–1.3 agreeing with in situ magnetosphere measurements
We report systematic differences between Chandra ACIS and XMM‐Newton EPIC‐pn Jovian spectra and the impact of these on opacity and quenching
A study of Jupiter's aurorae with XMM-Newton Branduardi-Raymont, G.; Bhardwaj, A.; Elsner, R. F. ...
Astronomy and astrophysics (Berlin),
02/2007, Letnik:
463, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present a detailed analysis of Jupiter's X-ray (0.2-10 keV) auroral emissions as observed over two XMM-Newton revolutions in Nov. 2003 and compare it with that of an earlier observation in Apr. ...2003. We discover the existence of an electron bremsstrahlung component in the aurorae, which accounts for essentially all the X-ray flux above 2 keV: its presence had been predicted but never detected for lack of sensitivity of previous X-ray missions. This bremsstrahlung component varied significantly in strength and spectral shape over the 3.5 days covered by the Nov. 2003 observation, displaying substantial hardening of the spectrum with increasing flux. This variability may be linked to the strong solar activity taking place at the time, and may be induced by changes in the acceleration mechanisms inside Jupiter's magnetosphere. As in Apr. 2003, the auroral spectra below 2 keV are best fitted by a superposition of line emission most likely originating from ion charge exchange, with OVII playing the dominant role. We still cannot resolve conclusively the ion species responsible for the lowest energy lines (around 0.3 keV), so the question of the origin of the ions (magnetospheric or solar wind) is still open. It is conceivable that both scenarios play a role in what is certainly a very complex planetary structure. High resolution spectra of the whole planet obtained with the XMM-Newton Reflection Grating Spectrometer in the range 0.5-1 keV clearly separate emission lines (mostly of iron) originating at low latitudes on Jupiter from the auroral lines due to oxygen. These are shown to possess very broad wings which imply velocities of ~5000 km s$^{\rm -1}$. Such speeds are consistent with the energies at which precipitating and charge exchanging oxygen ions are expected to be accelerated in Jupiter's magnetosphere. Overall we find good agreement between our measurements and the predictions of recently developed models of Jupiter's auroral processes.
Simultaneous Chandra X‐ray and Hubble Space Telescope FUV observations of Jupiter's aurorae carried out in February 2003 have been re‐examined to investigate the spatial morphology of the X‐ray ...events in different energy bands. The data clearly show that in the Northern auroral region (in the main auroral oval and the polar cap) events with energy > 2 keV are located at the periphery of those with energy < 2 keV and coincide with FUV bright features. In addition, X‐ray spectra extracted from the areas where the two event distributions are concentrated possess different shapes. We associate the > 2 keV events (∼45 MW emitted power) with the electron bremsstrahlung component recently revealed by XMM‐Newton in the spectra of Jupiter's aurorae, and the < 2 keV emission (∼230 MW) with the product of ion charge exchange, now established as the likely mechanism responsible for the soft X‐ray Jovian aurora. We suggest that the same population of energetic electrons may be responsible for both, the X‐ray bremsstrahlung and the FUV emission of Jupiter's aurorae. Comparison of the > 2 keV X‐ray and FUV (340 GW) powers measured during the observations shows that they are broadly consistent with the predicted emissions from a population of energetic electrons precipitating in the planet's atmosphere, thus supporting our interpretation.
Observations of Jupiter carried out by the Chandra Advanced CCD Imaging Spectrometer (ACIS-S) instrument over 24-26 February 2003 show that the auroral X-ray spectrum consists of line emission ...consistent with high-charge states of precipitating ions, and not a continuum as might be expected from bremsstrahlung. The part of the spectrum due to oxygen peaks around 650 eV, which indicates a high fraction of fully stripped oxygen in the precipitating ion flux. A combination of the OVIII emission lines at 653 eV and 774 eV, as well as the OVII emission lines at 561 eV and 666 eV, are evident in the measure auroral spectrum. There is also line emission at lower energies in the spectral region extending from 250 to 350 eV, which could be from sulfur and/or carbon. The Jovian auroral X-ray spectra are significantly different from the X-ray spectra of comets. The charge state distribution of the oxygen ions implied by the measured auroral X-ray spectra strongly suggests that independent of the source of the energetic ions, magnetospheric or solar wind, the ions have undergone additional acceleration. This spectral evidence for ion acceleration is also consistent with the relatively high intensities of the X rays compared with the available phase space density of the (unaccelerated) source populations of solar wind or magnetospheric ions at Jupiter, which are orders of magnitude too small to explain the observed emissions. The Chandra X-ray observations were executed simultaneously with observations at ultraviolet wavelengths by the Hubble Space Telescope and at radio wavelengths by the Ulysses spacecraft. These additional data sets suggest that the source of the X rays is magnetospheric in origin and that the precipitating particles are accelerated by strong field-aligned electric fields, which simultaneously create both the several-MeV energetic ion population and the relativistic electrons observed in situ by Ulysses that are correlated with approx.40 min quasi-periodic radio outbursts.
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