7,308 research outputs found
PCA of PCA: Principal Component Analysis of Partial Covering Absorption in NGC 1365
We analyse 400 ks of XMM-Newton data on the active galactic nucleus NGC 1365
using principal component analysis (PCA) to identify model independent spectral
components. We find two significant components and demonstrate that they are
qualitatively different from those found in MCG?6-30-15 using the same method.
As the variability in NGC 1365 is known to be due to changes in the parameters
of a partial covering neutral absorber, this shows that the same mechanism
cannot be the driver of variability in MCG-6-30-15. By examining intervals
where the spectrum shows relatively low absorption we separate the effects of
intrinsic source variability, including signatures of relativistic reflection,
from variations in the intervening absorption. We simulate the principal
components produced by different physical variations, and show that PCA
provides a clear distinction between absorption and reflection as the drivers
of variability in AGN spectra. The simulations are shown to reproduce the PCA
spectra of both NGC 1365 and MCG-6-30-15, and further demonstrate that the
dominant cause of spectral variability in these two sources requires a
qualitatively different mechanism.Comment: 8 pages, 10 figures. Accepted for publication in MNRA
Implications of very rapid TeV variability in blazars
We discuss the implications of rapid (few-minute) variability in the TeV flux
of blazars, which has been observed recently with the HESS and MAGIC
telescopes. The variability timescales seen in PKS 2155-304 and Mrk 501 are
much shorter than inferred light-crossing times at the black hole horizon,
suggesting that the variability involves enhanced emission in a small region
within an outflowing jet. The enhancement could be triggered by dissipation in
part of the black hole's magnetosphere at the base of the outflow, or else by
instabilities in the jet itself. By considering the energetics of the observed
flares, along with the requirement that TeV photons escape without producing
pairs, we deduce that the bulk Lorentz factors in the jets must be >50. The
distance of the emission region from the central black hole is less
well-constrained. We discuss possible consequences for multi-wavelength
observations.Comment: 5 pages, no figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Letter
Applying remote sensing and GIS techniques in solving rural county information needs
The project designed was to acquaint county government officials and their clientele with remote sensing and GIS products that contain information about land conditions and land use. Other users determined through the course of this project were federal agencies working at the county level, agricultural businesses and others in need of spatial information. The specific project objectives were: (1) to investigate the feasibility of using remotely sensed data to identify and quantify specific land cover categories and conditions for purposes of tax assessment, cropland area measurements and land use evaluation; (2) to investigate the use of satellite remote sensing data as an aid in assessing soil management practices; and (3) to evaluate the use of remotely sensed data to assess soil resources and conditions which affect productivity
Modelling the Extreme X-ray Spectrum of IRAS 13224-3809
The extreme NLS1 galaxy IRAS 13224-3809 shows significant variability,
frequency depended time lags, and strong Fe K line and Fe L features in the
long 2011 XMM-Newton observation. In this work we study the spectral properties
of IRAS 13224-3809 in detail, and carry out a series of analyses to probe the
nature of the source, focusing in particular on the spectral variability
exhibited. The RGS spectrum shows no obvious signatures of absorption by
partially ionised material (warm absorbers). We fit the 0.3-10.0 keV spectra
with a model that includes relativistic reflection from the inner accretion
disc, a standard powerlaw AGN continuum, and a low-temperature (~0.1 keV)
blackbody, which may originate in the accretion disc, either as direct or
reprocessed thermal emission. We find that the reflection model explains the
time-averaged spectrum well, and we also undertake flux-resolved and
time-resolved spectral analyses, which provide evidence of gravitational
light-bending effects. Additionally, the temperature and flux of the blackbody
component are found to follow the relation expected for simple
thermal blackbody emission from a constant emitting area, indicating a physical
origin for this component.Comment: 12 pages, 7 figures, accepted for publication in MNRA
On the changes of the electronic structure of early-transition-metal-systems at hydrogenation
The hydrogenation effect on Sc, Y, La, Cd and Eu has been investigated by XPS. The stability, the charge transfer as well as the microscopic behaviours of the processes have been discussed
Spin polarization of electron current through a potential barrier in two-dimensional structures with spin-orbit interaction
We show that an initially unpolarized electron flow acquires spin
polarization after passing through a lateral barrier in two-dimensional (2D)
system with spin-orbit interaction (SOI) even if the current is directed
normally to the barrier. The generated spin current depends on the distance
from the barrier. It oscillates with the distance in the vicinity of the
barrier and asymptotically reaches a constant value. The most efficient
generation of the spin current (with polarization above 50%) occurs, when the
Fermi energy is near the potential barrier maximum. Since the spin current in
SOI medium is not unambiguously defined we propose to pass this current from
the SOI region into a contacting region without SOI and show, that the spin
polarization loss under such transmission can be negligible.Comment: 11 pages, 6 figures, accepted for publication in Journal of Physics:
Condensed Matte
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