X‐ray emission from the outer planets: Albedo for scattering and fluorescence of solar X rays

Cravens, T. E.; Clark, J. F.; Bhardwaj, Anil; Elsner, Ronald F.; Waite, J. H.; Maurellis, A. N.; Gladstone, G. R.; Branduardi‐Raymont, G.

doi:10.1029/2005ja011413

Cited by 37 publications

(65 citation statements)

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“…More recent Chandra observations have provided us with a remarkable view of the X-ray morphology of the Saturnian system, and of its temporal behaviour in the X-rays: both the planet's disk and the rings have been separately detected, and strong variability, closely following the behaviour of the solar X-ray flux, has been discovered in the disk X-ray emission (Bhardwaj et al 2005a,b). This suggests that its origin may lie in the scattering of solar X-rays in the upper layers of Saturn's atmosphere, as is the case for Jupiter's disk emission (Bhardwaj et al 2005cCravens et al 2006). Unlike Jupiter, though, no difference is found in the spectral characteristics of Saturn's disk and polar emissions, thus no evidence for X-rays of auroral origin is provided by the Chandra data.…”

Section: Introductionmentioning

confidence: 60%

“…As expected, there appears to be correlation between Saturn's disk X-ray power and the solar X-ray flux. For comparison, the same parameters are also plotted for Jupiter's disk (filled circles), which also has been shown to act as a mirror of solar X-rays (Maurellis et al 2000;Bhardwaj et al 2005c;Cravens et al 2006). XMM-Newton and Chandra observations in Fig.…”

Section: Separating Saturn's Disk and Rings X-ray Emissionmentioning

confidence: 99%

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X-rays from Saturn: a study withXMM-NewtonandChandraover the years 2002–05

Branduardi‐Raymont¹,

Bhardwaj²,

Elsner³

et al. 2010

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Aims. We approach the study of Saturn and its environment in a novel way using X-ray data, by making a systematic and uniform spectral analysis of all the X-ray observations of the planet to date. Methods. We present the results of the two most recent (2005) XMM-Newton observations of Saturn together with the re-analysis of an earlier (2002) observation from the XMM-Newton archive and of three Chandra observations in 2003 and 2004. While the XMM-Newton telescope resolution does not enable us to resolve spatially the contributions of the planet's disk and rings to the X-ray flux, we can estimate their strengths and their evolution over the years from spectral analysis, and compare them with those observed with Chandra. Results. The spectrum of the X-ray emission is well fitted by an optically thin coronal model with an average temperature of 0.5 keV. The addition of a fluorescent oxygen emission line at ∼0.53 keV improves the fits significantly. In accordance with earlier reports, we interpret the coronal component as emission from the planetary disk, produced by the scattering of solar X-rays in Saturn's upper atmosphere, and the line as originating from the Saturnian rings. The strength of the disk X-ray emission is seen to decrease over the period [2002][2003][2004][2005], following the decay of solar activity towards the current minimum in the solar cycle. By comparing the relative fluxes of the disk X-ray emission and the oxygen line, we suggest that the line strength does not vary over the years in the same fashion as the disk flux. We consider possible alternatives for the origin of the line. The connection between solar activity and the strength of Saturn's disk X-ray emission is investigated and compared with that of Jupiter. We also discuss the apparent lack of X-ray aurorae on Saturn; by comparing the planet's parameters relevant to aurora production with those of Jupiter we conclude that Saturnian X-ray aurorae are likely to have gone undetected because they are below the sensitivity threshold of current Earth-bound observatories. A similar comparison for Uranus and Neptune leads to the same disappointing conclusion, which is likely to hold true also with the planned next generation International X-ray Observatory. The next step in advancing this research can only be realised with in-situ X-ray observations at the planets.

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Section: Introductionmentioning

confidence: 60%

Section: Separating Saturn's Disk and Rings X-ray Emissionmentioning

confidence: 99%

X-rays from Saturn: a study withXMM-NewtonandChandraover the years 2002–05

Branduardi‐Raymont¹,

Bhardwaj²,

Elsner³

et al. 2010

A&A

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“…4: OVII photons are well separated spatially into the two aurorae, while the other lines are filling in the low latitude/cross dispersion range. In particular, this is true for the FeXVII lines at 15 and 17 Å, which are known to be associated with the planet's disk and are thought to be scattered solar X-rays (BR1, Maurellis et al 2000;Cravens et al 2006). Unfortunately, the combination of lower RGS sensitivity and low source flux at the short and long wavelength ends of the instrument operational range is such that Jupiter's spectrum is only significantly detected in the range 13−23 Å (0.54−0.95 keV), to which we have restricted subsequent spectral fitting.…”

Section: Rgs Spectramentioning

confidence: 99%

“…The line is likely to be residual contamination by the disk emission, which may become more evident above ∼1 keV where the ion contribution to the auroral emission is decreasing rapidly. We know that the disk acts as a mirror for solar X-rays (Maurellis et al 2000, Cravens et al 2006): Bhardwaj et al (2005 have shown that a very large solar flare took place at a time such that Jupiter's response to it would have been observable by XMM-Newton had it not been switched off during perigee passage between revs 0726 and 0727. Possibly part of this response to the flare, Jupiter's disk emission is seen to be overall brighter by ∼40%, and the flux of the MgXI line from the disk to be three times larger, in rev.…”

Section: The Ion Componentmentioning

confidence: 99%

“…The X-ray spectrum of Jupiter's low latitude disk regions is different, and matches that of solar X-rays scattered in the planet's upper atmosphere (BR1; see also Maurellis et al 2000;Cravens et al 2006). A temporal study of Jupiter's low latitude disk emission during the Nov. 2003 XMM-Newton observation and of its relationship to the solar X-ray flux is presented in Bhardwaj et al (2005), while a spectral analysis of the disk emission is given in Branduardi-Raymont et al (2006).…”

Section: Introductionmentioning

confidence: 99%

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A study of Jupiter's aurorae with XMM-Newton

Branduardi‐Raymont

Bhardwaj

Elsner

et al. 2006

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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 −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.

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The impact of an ICME on the Jovian X‐ray aurora

et al. 2016

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We report the first Jupiter X‐ray observations planned to coincide with an interplanetary coronal mass ejection (ICME). At the predicted ICME arrival time, we observed a factor of ∼8 enhancement in Jupiter's X‐ray aurora. Within 1.5 h of this enhancement, intense bursts of non‐Io decametric radio emission occurred. Spatial, spectral, and temporal characteristics also varied between ICME arrival and another X‐ray observation two days later. Gladstone et al. (2002) discovered the polar X‐ray hot spot and found it pulsed with 45 min quasiperiodicity. During the ICME arrival, the hot spot expanded and exhibited two periods: 26 min periodicity from sulfur ions and 12 min periodicity from a mixture of carbon/sulfur and oxygen ions. After the ICME, the dominant period became 42 min. By comparing Vogt et al. (2011) Jovian mapping models with spectral analysis, we found that during ICME arrival at least two distinct ion populations, from Jupiter's dayside, produced the X‐ray aurora. Auroras mapping to magnetospheric field lines between 50 and 70 RJ were dominated by emission from precipitating sulfur ions (S7+,…,14+). Emissions mapping to closed field lines between 70 and 120 RJ and to open field lines were generated by a mixture of precipitating oxygen (O7+,8+) and sulfur/carbon ions, possibly implying some solar wind precipitation. We suggest that the best explanation for the X‐ray hot spot is pulsed dayside reconnection perturbing magnetospheric downward currents, as proposed by Bunce et al. (2004). The auroral enhancement has different spectral, spatial, and temporal characteristics to the hot spot. By analyzing these characteristics and coincident radio emissions, we propose that the enhancement is driven directly by the ICME through Jovian magnetosphere compression and/or a large‐scale dayside reconnection event.

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X‐ray emission from the outer planets: Albedo for scattering and fluorescence of solar X rays

Cited by 37 publications

References 32 publications

X-rays from Saturn: a study withXMM-NewtonandChandraover the years 2002–05

X-rays from Saturn: a study withXMM-NewtonandChandraover the years 2002–05

A study of Jupiter's aurorae with XMM-Newton

The impact of an ICME on the Jovian X‐ray aurora

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