arXiv subjects

A. Bhardwaj

Publications and source records attributed to A. Bhardwaj.

41 records · Page 3Linked to original sources

arXiv2006

A study of Jupiter's aurorae with XMM-Newton

We present a detailed analysis of Jupiter's X-ray (0.2-10 keV) auroral emissions as observed by XMM-Newton in Nov. 2003 and compare it with that of an Apr. 2003 observation. 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 RGS in the range 0.5-1 keV clearly separate emission lines (mostly of Fe) originating at low latitudes on Jupiter from the auroral lines due to O. These are shown to possess very broad wings which imply velocities of ~5000 km/s. Such speeds are consistent with the energies at which precipitating and charge exchanging O ions are expected to be accelerated in Jupiter's magnetosphere. Overall we find good agreement between our measurements and the predictions of recent models.

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arXiv2006

Latest results on Jovian disk X-rays from XMM-Newton

We present the results of a spectral study of the soft X-ray emission (0.2-2.5 keV) from low-latitude (`disk') regions of Jupiter. The data were obtained during two observing campaigns with XMM-Newton in April and November 2003. While the level of the emission remained approximately the same between April and the first half of the November observation, the second part of the latter shows an enhancement by about 40% in the 0.2-2.5 keV flux. A very similar, and apparently correlated increase, in time and scale, was observed in the solar X-ray and EUV flux. The months of October and November 2003 saw a period of particularly intense solar activity, which appears reflected in the behaviour of the soft X-rays from Jupiter's disk. The X-ray spectra, from the XMM-Newton EPIC CCD cameras, are all well fitted by a coronal model with temperatures in the range 0.4-0.5 keV, with additional line emission from Mg XI (1.35 keV) and Si XIII (1.86 keV): these are characteristic lines of solar X-ray spectra at maximum activity and during flares. The XMM-Newton observations lend further support to the theory that Jupiter's disk X-ray emission is controlled by the Sun, and may be produced in large part by scattering, elastic and fluorescent, of solar X-rays in the upper atmosphere of the planet.

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arXiv2005

XMM-Newton observations of X-ray emission from Jupiter

We present the results of two XMM-Newton observations of Jupiter carried out in 2003 for 100 and 250 ks (or 3 and 7 planet rotations) respectively. X-ray images from the EPIC CCD cameras show prominent emission from the auroral regions in the 0.2 - 2.0 keV band: the spectra are well modelled by a combination of emission lines, including most prominently those of highly ionised oxygen (OVII and OVIII). In addition, and for the first time, XMM-Newton reveals the presence in both aurorae of a higher energy component (3 - 7 keV) which is well described by an electron bremsstrahlung spectrum. This component is found to be variable in flux and spectral shape during the Nov. 2003 observation, which corresponded to an extended period of intense solar activity. Emission from the equatorial regions of Jupiter's disk is also observed, with a spectrum consistent with that of solar X-rays scattered in the planet's upper atmosphere. Jupiter's X-rays are spectrally resolved with the RGS which clearly separates the prominent OVII contribution of the aurorae from the OVIII, FeXVII and MgXI lines, originating in the low-latitude disk regions of the planet.

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arXiv2002

Soft X-ray Emissions from Planets, Moons, and Comets

A wide variety of solar system bodies are now known to radiate in the soft x-ray energy (<5 keV) regime. These include planets (Earth, Jupiter, Venus, Saturn, Mars): bodies having thick atmospheres, with or without intrinsic magnetic field; planetary satellites (Moon, Io, Europa, Ganymede): bodies with thin or no atmospheres; and comets and the Io plasma torus: bodies having extended tenuous atmospheres. Several different mechanisms have been proposed to explain the generation of soft x-rays from these objects, whereas in the hard x-ray energy range (>10 keV) x-rays result mainly from the electron bremsstrahlung process. In this paper we present a brief review of the x-ray observations on each of the planetary bodies and discuss their characteristics and proposed source mechanisms.

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arXiv2002

I0-Jupiter system: A unique case of Moon-Planet interaction

Io and Jupiter constitute a moon-planet system that is unique in our solar system. Io is the most volcanically active planetary body, while Jupiter is the first among the planets in terms of size, mass, magnetic field strength, spin rate, and volume of the magnetosphere. That Io is electrodynamically linked to Jupiter is known for nearly four decades from the radio emissions. Io influences Jupiter by supplying heavy ions to its magnetosphere, which dominates its energetic and dynamics. Jupiter influences Io by tidally heating its interior, which in turn drives the volcanic activity on Io. The role of Io and Jupiter in their mutual interaction and the nature of their coupling were first elaborated in greater detail by the two Voyagers flybys in 1979. Subsequent exploration of this system by ground-based and Earth-satellite-borne observatories and by the Galileo orbiter mission has improved our understanding of the highly complex electrodynamical interaction between Io and Jupiter many fold. A distinct feature of this interaction has been discovered in Jupiter's atmosphere as a auroral-like bright emission spot along with a comet-like tail in infrared (IR), ultraviolet (UV), and visible wavelengths at the foot of Io flux tube (IFT). The HST and Galileo and Cassini imagining experiments have observed emissions from the Io's atmosphere at UV and visible wavelengths, which could be produced by energetic electrons in IFT. In this paper an overview on these aspects of the Io-Jupiter system is presented, which by virtue of its electrodynamical coupling, has implications for the extra-solar planetary system and binary stars.

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