3,204 research outputs found
Iron-Line Emission as a Probe of Bardeen-Petterson Accretion Disks
In this work we show that Bardeen-Petterson accretion disks can exhibit
unique, detectable features in relativistically broadened emission line
profiles. Some of the unique characteristics include inverted line profiles
with sharper red horns and softer blue horns and even profiles with more than 2
horns from a single rest-frame line. We demonstrate these points by
constructing a series of synthetic line profiles using simple two-component
disk models. We find that the resultant profiles are very sensitive to the two
key parameters one would like to constrain, namely the Bardeen-Petterson
transition radius r_{BP} and the relative tilt \beta between the two disk
components over a range of likely values [10 < r_{BP}/(GM/c^2) < 40 ; 15deg <
\beta < 45deg]. We use our findings to show that some of the ``extra'' line
features observed in the spectrum of the Seyfert-I galaxy MCG--6-30-15 may be
attributable to a Bardeen-Petterson disk structure. Similarly, we apply our
findings to two likely Bardeen-Petterson candidate Galactic black holes - GRO
J1655-40 and XTE J1550-564. We provide synthetic line profiles of these systems
using observationally constrained sets of parameters. Although we do not
formally fit the data for any of these systems, we confirm that our synthetic
spectra are consistent with current observations.Comment: 13 pages, 11 figures, submitted to Ap
Quantum oscillations in the parent pnictide BaFeAs : itinerant electrons in the reconstructed state
We report quantum oscillation measurements that enable the direct observation
of the Fermi surface of the low temperature ground state of \ba122. From these
measurements we characterize the low energy excitations, revealing that the
Fermi surface is reconstructed in the antiferromagnetic state, but leaving
itinerant electrons in its wake. The present measurements are consistent with a
conventional band folding picture of the antiferromagnetic ground state,
placing important limits on the topology and size of the Fermi surface.Comment: 5 pages, 3 figure
Properties of metastable alkaline-earth-metal atoms calculated using an accurate effective core potential
The first three electronically excited states in the alkaline-earth-metal
atoms magnesium, calcium, and strontium comprise the (nsnp) triplet P^o_J
(J=0,1,2) fine-structure manifold. All three states are metastable and are of
interest for optical atomic clocks as well as for cold-collision physics. An
efficient technique--based on a physically motivated potential that models the
presence of the ionic core--is employed to solve the Schroedinger equation for
the two-electron valence shell. In this way, radiative lifetimes, laser-induced
clock shifts, and long-range interaction parameters are calculated for
metastable Mg, Ca, and Sr.Comment: 13 pages, 9 table
Signatures of High-Intensity Compton Scattering
We review known and discuss new signatures of high-intensity Compton
scattering assuming a scenario where a high-power laser is brought into
collision with an electron beam. At high intensities one expects to see a
substantial red-shift of the usual kinematic Compton edge of the photon
spectrum caused by the large, intensity dependent, effective mass of the
electrons within the laser beam. Emission rates acquire their global maximum at
this edge while neighbouring smaller peaks signal higher harmonics. In
addition, we find that the notion of the centre-of-mass frame for a given
harmonic becomes intensity dependent. Tuning the intensity then effectively
amounts to changing the frame of reference, going continuously from inverse to
ordinary Compton scattering with the centre-of-mass kinematics defining the
transition point between the two.Comment: 25 pages, 16 .eps figure
Reprocessing with GANEX:Methodology for Ligand Radiation Tolerance Testing
Results demonstrating the methodology for testing the radiation tolerance of organic ligands are presented. A high activity sealed source was used to irradiate samples which were sequentially removed and analysed using a sensitive mass spectrometer. The degradation of a candidate ligand for a new reprocessing process “GANEX” was found to be around 50% after 567 kGy exposure to gamma from Cs-137.<br/
DBI Inflation using a One-Parameter Family of Throat Geometries
We demonstrate the possibility of examining cosmological signatures in the
DBI inflation setup using the BGMPZ solution, a one-parameter family of
geometries for the warped throat which interpolate between the Maldacena-Nunez
and Klebanov-Strassler solutions. The warp factor is determined numerically and
subsequently used to calculate cosmological observables including the scalar
and tensor spectral indices, for a sample point in the parameter space. As one
moves away from the KS solution for the throat the warp factor is qualitatively
different, which leads to a significant change for the observables, but also
generically increases the non-Gaussianity of the models. We argue that the
different models can potentially be differentiated by current and future
experiments.Comment: 17 pages, 10 figures; v2: section 4 expanded, references added; v3:
typos fixe
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