5,789 research outputs found
Statistical evaluation of the flux cross-calibration of the XMM-Newton EPIC cameras
The second XMM-Newton serendipitous source catalogue, 2XMM, provides the
ideal data base for performing a statistical evaluation of the flux
cross-calibration of the XMM-Newton European Photon Imaging Cameras (EPIC). We
aim to evaluate the status of the relative flux calibration of the EPIC cameras
on board XMM-Newton (MOS1, MOS2, and pn) and investigate the dependence of the
calibration on energy, position in the field of view of the X-ray detectors,
and lifetime of the mission. We compiled the distribution of flux percentage
differences for large samples of 'good quality' objects detected with at least
two of the EPIC cameras. The mean offset of the fluxes and dispersion of the
distributions was then found by Gaussian fitting. Count rate to flux conversion
was performed with a fixed spectral model. The impact on the results of varying
this model was investigated. Excellent agreement was found between the two EPIC
MOS cameras to better than 4% from 0.2 keV to 12.0 keV. MOS cameras register
7-9% higher flux than pn below 4.5 keV and 10-13% flux excess above 4.5 keV. No
evolution of the flux ratios is seen with time, except at energies below 0.5
keV, where we found a strong decrease in the MOS to pn flux ratio with time.
This effect is known to be due to a gradually degrading MOS redistribution
function. The flux ratios show some dependence on distance from the optical
axis in the sense that the MOS to pn flux excess increases with off-axis angle.
Furthermore, in the 4.5-12.0 keV band there is a strong dependence of the MOS
to pn excess flux on the azimuthal-angle. These results strongly suggest that
the calibration of the Reflection Grating Array (RGA) blocking factors is
incorrect at high energies. Finally, we recommend ways to improve the
calculation of fluxes in future versions of XMM-Newton source catalogues.Comment: 11 pages, 10 figures, 3 tables. Abridged Abstract. Accepted for
publication in Astronomy and Astrophysic
Perfectly invisible -symmetric zero-gap systems, conformal field theoretical kinks, and exotic nonlinear supersymmetry
We investigate a special class of the -symmetric quantum models
being perfectly invisible zero-gap systems with a unique bound state at the
very edge of continuous spectrum of scattering states. The family includes the
-regularized two particle Calogero systems (conformal quantum
mechanics models of de Alfaro-Fubini-Furlan) and their rational extensions
whose potentials satisfy equations of the KdV hierarchy and exhibit,
particularly, a behaviour typical for extreme waves. We show that the two
simplest Hamiltonians from the Calogero subfamily determine the fluctuation
spectra around the -regularized kinks arising as traveling waves
in the field-theoretical Liouville and conformal Toda systems. Peculiar
properties of the quantum systems are reflected in the associated exotic
nonlinear supersymmetry in the unbroken or partially broken phases. The
conventional supersymmetry is extended here to the
nonlinear supersymmetry that involves two bosonic generators
composed from Lax-Novikov integrals of the subsystems, one of which is the
central charge of the superalgebra. Jordan states are shown to play an
essential role in the construction.Comment: 33 pages; comments and refs added, version to appear in JHE
General Criterion for the existence of Supertube and BIon in Curved Target Space
The supertube and BIon spike solutions are examined in a general curved
target space. The criteria for the existence of these solutions are explicitly
derived. Also the equation which the general BIon solution should satisfy is
derived.Comment: 12 pages, no figur
Anticipated synchronization in coupled inertia ratchets with time-delayed feedback: a numerical study
We investigate anticipated synchronization between two periodically driven
deterministic, dissipative inertia ratchets that are able to exhibit directed
transport with a finite velocity. The two ratchets interact through an
unidirectional delay coupling: one is acting as a master system while the other
one represents the slave system. Each of the two dissipative deterministic
ratchets is driven externally by a common periodic force. The delay coupling
involves two parameters: the coupling strength and the (positive-valued) delay
time. We study the synchronization features for the unbounded, current carrying
trajectories of the master and the slave, respectively, for four different
strengths of the driving amplitude. These in turn characterize differing phase
space dynamics of the transporting ratchet dynamics: regular, intermittent and
a chaotic transport regime. We find that the slave ratchet can respond in
exactly the same way as the master will respond in the future, thereby
anticipating the nonlinear directed transport
ac-driven Brownian motors: a Fokker-Planck treatment
We consider a primary model of ac-driven Brownian motors, i.e., a classical
particle placed in a spatial-time periodic potential and coupled to a heat
bath. The effects of fluctuations and dissipations are studied by a
time-dependent Fokker-Planck equation. The approach allows us to map the
original stochastic problem onto a system of ordinary linear algebraic
equations. The solution of the system provides complete information about
ratchet transport, avoiding such disadvantages of direct stochastic
calculations as long transients and large statistical fluctuations. The
Fokker-Planck approach to dynamical ratchets is instructive and opens the space
for further generalizations
Supersphere
The spherical D2-brane solution is obtained without RR external background.
The solution is shown to preserve supersymmetries. The configurations
obtained depend on the integration constant . For the shape
of the solution is a deformed sphere. When, however, , the D2-brane
system seems to exhibit a brane-anti-brane configuration.Comment: 11 pages, 2 figure
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