104,715 research outputs found
Fluoride ion reactions of fluorocarbon derivations Final report
Relative reactivity of unsaturated fluorocarbon derivatives toward cesium fluorid
Simultaneous spectral and reverberation modelling of relativistic reflection in Mrk 335
We present an X-ray spectral and timing model to investigate the broad and
variable iron line seen in the high flux state of Mrk 335. The model consists
of a variable X-ray source positioned along the rotation axis of the black hole
that illuminates the accretion disc producing a back-scattered, ionized
reflection spectrum. We compute time lags including full dilution effects and
perform simultaneous fitting of the 2-10 keV spectrum and the
frequency-dependent time lags of 2.5-4 vs. 4-6.5 keV bands. The best-fitting
parameters are consistent with a black hole mass of approximately 1.3 x 10^7
M_sun, disc inclination of 45 degrees and the photon index of the direct
continuum of 2.4. The iron abundance is 0.5 and the ionization parameter is
10^3 erg cm / s at the innermost part of the disc and decreases further out.
The X-ray source height is very small, approximately 2 r_g. Furthermore, we fit
the Fe L lags simultaneously with the 0.3-10 keV spectrum. The key parameters
are comparable to those previously obtained. We also report the differences
below 2 keV using the xillver and reflionx models which could affect the
interpretation of the soft excess. While simultaneously fitting spectroscopic
and timing data can break the degeneracy between the source height and the
black hole mass, we find that the measurements of the source height and the
central mass significantly depend on the ionization state of the disc and are
possibly model-dependent.Comment: 11 pages, 8 figures, accepted for publication in MNRA
The complex geomety of a domain related to -synthesis
We describe the basic complex geometry and function theory of the {\em
pentablock} , which is the bounded domain in given
by where denotes
the open unit ball in the space of complex matrices. We prove
several characterizations of the domain. We describe its distinguished boundary
and exhibit a -parameter group of automorphisms of . We show
that is intimately connected with the problem of -synthesis
for a certain cost function on the space of matrices defined
in connection with robust stabilization by control engineers. We demonstrate
connections between the function theories of and . We
show that is polynomially convex and starlike.Comment: 36 pages, 2 figures. This version contains corrections of some
inaccuracies and an expanded argument for Proposition 12.
X-ray time lags in AGN: inverse-Compton scattering and spherical corona model
We develop a physically motivated, spherical corona model to investigate the
frequency-dependent time lags in AGN. The model includes the effects of Compton
up-scattering between the disc UV photons and coronal electrons, and the
subsequent X-ray reverberation from the disc. The time lags are associated with
the time required for multiple scatterings to boost UV photons up to soft and
hard X-ray energies, and the light crossing time the photons take to reach the
observer. This model can reproduce not only low-frequency hard and
high-frequency soft lags, but also the clear bumps and wiggles in reverberation
profiles which should explain the wavy-residuals currently observed in some
AGN. Our model supports an anti-correlation between the optical depth and
coronal temperatures. In case of an optically thin corona, time delays due to
propagating fluctuations may be required to reproduce observed time lags. We
fit the model to the lag-frequency data of 1H0707-495, Ark 564, NGC 4051 and
IRAS 13224-3809 estimated using the minimal bias technique so that the observed
lags here are highest-possible quality. We find their corona size is ~7-15 r_g
having the constrained optical depth ~2-10. The coronal temperature is ~150-300
keV. Finally, we note that the reverberation wiggles may be signatures of
repeating scatters inside the corona that control the distribution of X-ray
sources.Comment: 15 pages, 10 figures, accepted for publication in MNRA
Iron line profiles including emission from within the innermost stable orbit of a black hole accretion disc
Reynolds & Begelman (1997) have recently proposed a model in which the broad
and extremely redshifted iron line seen during a deep minimum of the light
curve of the Seyfert 1 galaxy MCG-6-30-15 originates from matter spiralling
into a Schwarzschild black hole, contrary to previous claims that the black
hole may be spinning rapidly (Iwasawa et al 1996; Dabrowski et al 1997). Here
we calculate in detail the X-ray spectrum produced by their model using the
full reflected continuum emission, including absorption features. This
calculation takes into account the doppler and relativistic effects. For the
range of parameters we consider, we find that the spectrum should show a large
photoelectric absorption edge of iron, which is not seen in the data. The
absorption edge is a consequence of the line emitting matter within the
innermost stable orbit being highly ionized, and is largely independent of the
parameters chosen for their model. If we restrict our attention to the 3-10 keV
band we may effectively remove this absorption edge by fitting a steeper power
law, but this results in a significant underprediction of the 0.4-0.5 keV flux.
We conclude that the data on MCG-6-30-15 are more consistent with the Kerr than
the Schwarzschild model.Comment: 5 pages with 5 postscript figures. Accepted for publication in MNRA
Defect energy of infinite-component vector spin glasses
We compute numerically the zero temperature defect energy, Delta E, of the
vector spin glass in the limit of an infinite number of spin components m, for
a range of dimensions 2 <= d <= 5. Fitting to Delta E ~ L^theta, where L is the
system size, we obtain: theta = -1.54 (d=2), theta = -1.04 (d=3), theta = -0.67
(d=4) and theta = -0.37 (d=5). These results show that the lower critical
dimension, d_l (the dimension where theta changes sign), is significantly
higher for m=infinity than for finite m (where 2 < d_l < 3).Comment: 4 pages, 5 figure
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