795 research outputs found
The X-ray emission of magnetic cataclysmic variables in the XMM-Newton era
We review the X-ray spectral properties of magnetic cataclysmic binaries
derived from observations obtained during the last decade with the large X-ray
observatories XMM-Newton, Chandra and Suzaku. We focus on the signatures of the
different accretion modes which are predicted according to the values of the
main physical parameters (magnetic field, local accretion rate and white dwarf
mass). The observed large diversity of spectral behaviors indicates a wide
range of parameter values in both intermediate polars and polars, in line with
a possible evolutionary link between both classes.Comment: To appear in the Proceedings of "The Golden Age of Cataclysmic
Variables (Palermo 2011)", in Mem. Soc. Astron. It. (7 pages, 3 figures
Rapport sur une prospection épidémiologique et entomologique dans la subdivision de Djoum du 23 au 30 Juin 1955
Influence of classical resonances on chaotic tunnelling
Dynamical tunnelling between symmetry-related stable modes is studied in the
periodically driven pendulum. We present strong evidence that the tunnelling
process is governed by nonlinear resonances that manifest within the regular
phase-space islands on which the stable modes are localized. By means of a
quantitative numerical study of the corresponding Floquet problem, we identify
the trace of such resonances not only in the level splittings between
near-degenerate quantum states, where they lead to prominent plateau
structures, but also in overlap matrix elements of the Floquet eigenstates,
which reveal characteristic sequences of avoided crossings in the Floquet
spectrum. The semiclassical theory of resonance-assisted tunnelling yields good
overall agreement with the quantum-tunnelling rates, and indicates that partial
barriers within the chaos might play a prominent role
Unexplained high sensitivity of the reflectance of porous natural photonic structures to the presence of gases and vapours in the atmosphere
Entretien hivernovernal du virus myxomateux dans les terriers : myxomatose d'inoculation par la puce du lapin et myxomatose de fouissement
La résistance aux insecticides chez CULEX PIPIENS FATIGANS Wied. et les problèmes d'hygiène urbaine au Cameroun
The peculiar source XSS J12270-4859: a LMXB detected by FERMI ?
The X-ray source XSS J12270-4859 has been first suggested to be a magnetic
cataclysmic variable of Intermediate Polar type on the basis of its optical
spectrum and a possible 860 s X-ray periodicity. However further X-ray
observations by the Suzaku and XMM-Newton satellites did not confirm this
periodicity but show a very peculiar variability, including moderate repetitive
flares and numerous absorption dips. These characteristics together with a
suspected 4.3 h orbital period would suggest a possible link with the so-
called "dipping sources", a sub-class of Low-Mass X-ray Binaries (LMXB). Based
on the released FERMI catalogues, the source was also found coincident with a
very high energy (0.1-300 GeV) VHE source 2FGL J1227.7-4853. The good
positional coincidence, together with the lack of any other bright X-ray
sources in the field, makes this identification highly probable. However, none
of the other standard LMXBs have been so far detected by FERMI. Most galactic
VHE sources are associated with rotation-powered pulsars. We present here new
results obtained from a 30 ksec high-time resolution XMM observations in
January 2011 that confirm the flaring-dipping behaviour and provide upper
limits on fast X-ray pulsations. We discuss the possible association of the
source with either a microquasar or an accreting rotation powered pulsar.Comment: To appear in the Proceedings of "The Golden Age of Cataclysmic
Variables (Palermo 2011)", in Mem. Soc. Astron. It. (4 pages, 2 figures
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