903 research outputs found
X-rays from Saturn: A study with XMM-Newton and Chandra over the years 2002-05
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. 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 -
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 and conclude that
they are likely to lie below the sensitivity threshold of current Earth-bound
observatories. A similar comparison for Uranus and Neptune leads to the same
disappointing conclusion.Comment: 10 pages, 5 figures; to be published in 'Astronomy and Astrophysics
X-ray spectroscopy of the IP PQ Gem
Using RXTE and ASCA data, we investigate the roles played by occultation and absorption in the X-ray spin pulse profile of the intermediate polar PQ Gem. From the X-ray light curves and phase-resolved spectroscopy, we find that the intensity variations are the result of a combination of varying degrees of absorption and the accretion regions rotating behind the visible face of the white dwarf. These occultation and absorption effects are consistent with those expected from the accretion structures calculated from optical polarization data. We can reproduce the changes in absorber covering fraction either from geometrical effects, or by considering that the material in the leading edge of the accretion curtain is more finely fragmented than in other parts of the curtain. We determine a white dwarf mass of ⌠1.2 using the RXTE data
Estimation of microscopic averages from metadynamics
With the help of metadynamics it is possible to calculate efficiently the
free energy of systems displaying high energy barriers as a function of few
selected "collective variables". In doing this, the contribution of all the
other degrees of freedom ("microscopic" variables) is averaged out and, thus,
lost. In the following, it is shown that it is possible to calculate the
thermal average of these microscopic degrees of freedom during the
metadynamics, not loosing this piece of information
The nature and origin of Seyfert warm absorbers
We collate the results of recent high resolution X-ray spectroscopic observations of 23 AGN, and use the resulting information to try to provide answers to some of the main open questions about warm absorbers: where do they originate, what effect do they have on their host galaxies, and what is their importance within the energetics and dynamics of the AGN system as a whole? We find that the warm absorbers of nearby Seyferts and certain QSOs are most likely to originate in outflows from the dusty torus, and that the kinetic luminosity of these outflows accounts for well under 1% of the bolometric luminosities of the AGN. Our analysis supports, however, the view that the relativistic outflows recently observed in two PG quasars have their origin in accretion disc winds, although the energetic importance of these outflows is similar to that of the Seyfert warm absorbers. We find that the observed soft X-ray absorbing ionisation phases fill less than 10% of the available volume. Finally, we show that the amount of matter processed through an AGN outflow system, over the lifetime of the AGN, is probably large enough to have a significant influence on the evolution of the host galaxy and of the AGN itself
XMM-Newton observations of the Seyfert 1 AGN H0557-385
We present XMM-Newton observations of the Seyfert 1 AGN H0557-385. We have
conducted a study into the warm absorber present in this source, and using
high-resolution RGS data we find that the absorption can be characterised by
two phases: a phase with log ionisation parameter xi of 0.50 (where xi is in
units of ergs cm/s) and a column of 0.2e21 cm^-2, and a phase with log xi of
1.62 and a column of 1.3e22 cm^-2. An iron K alpha line is detected. Neutral
absorption is also present in the source, and we discuss possible origins for
this. On the assumption that the ionised absorbers originate as an outflow from
the inner edge of the torus, we use a new method for finding the volume filling
factor. Both phases of H0557-385 have small volume filling factors (< 1%). We
also derive the volume filling factors for a sample of 23 AGN using this
assumption and for the absorbers with log xi > 0.7 we find reasonable agreement
with the filling factors obtained through the alternative method of equating
the momentum flow of the absorbers to the momentum loss of the radiation field.
By comparing the filling factors obtained by the two methods, we infer that
some absorbers with log xi < 0.7 occur at significantly larger distances from
the nucleus than the inner edge of the torus.Comment: Accepted for publication in MNRA
Soft X-ray emission lines from a relativistic accretion disk in MCG-6-30-15 and Mrk 766
XMM-Newton Reflection Grating Spectrometer (RGS) spectra of the Narrow Line Seyfert 1 galaxies MCG -6-30-15 and Mrk 766 are physically and spectroscopically inconsistent with standard models comprising a power-law continuum absorbed by either cold or ionized matter. We propose that the remarkably similar features detected in both objects in the 5-35 Angstrom band are H-like oxygen, nitrogen, and carbon emission lines, gravitationally redshifted and broadened by relativistic effects in the vicinity of a Kerr black hole. We discuss the implications of our interpretation, and demonstrate that the derived parameters can be physically self-consistent
Subsolar magnetopause and cusp positions: comparison of MHD and empirical models
We simulate temporal variations of the subsolar magnetopause and cusp positions using global magnetohydrodynamic (MHD) models and compare predictions with the corresponding empirical models. In the second part, we calculate X-ray images from the MHD simulations. Results of this work can be used in preparation to the forthcoming SMILE mission
Progress of Solar Wind Magnetosphere Ionosphere Link Explorer (SMILE) Mission
SMILE (Solar wind Magnetosphere Ionosphere Link Explorer) mission is a joint ESA-CAS space science project. The working orbit is a 19 Re 5000 km HEO with 4 scientific instruments:Soft X-ray Imager(SXI), Ultra-Violet Imager (UVI), Magnetometer (MAG) and Light Ion Analyzer (LIA). SMILE aims to understand the interaction between the solar wind and the Earth's magnetosphere through the images of SXI and UVI and in-situ measurement from LIA and MAG. After the kick-off in 2016, the SMILE project went to Phase A study. The mission adoption is scheduled for November 2018, with a target launch date in 2022-2023. In this paper, the background of the mission, scientific objectives, the design and characteristics of scientific instruments and the mission outline will be introduced in details
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