10,272 research outputs found
On critical pilot tasks
Critical pilot performance in decision making proces
GRMHD prediction of coronal variability in accreting black holes
On the basis of data from an energy-conserving 3D general relativistic MHD
simulation, we predict the statistical character of variability in the coronal
luminosity from accreting black holes. When the inner boundary of the corona is
defined to be the electron scattering photosphere, its location depends only on
the mass accretion rate in Eddington units (\dot{M}). Nearly independent of
viewing angle and \dot{M}, the power spectrum over the range of frequencies
from approximately the orbital frequency at the innermost stable circular orbit
(ISCO) to ~100 times lower is well approximated by a power-law with index -2,
crudely consistent with the observed power spectra of hard X-ray fluctuations
in AGN and the hard states of Galactic binary black holes. The underlying
physical driver for variability in the light curve is variations in the
accretion rate caused by the chaotic character of MHD turbulence, but the power
spectrum of the coronal light output is significantly steeper. Part of this
contrast is due to the fact that the mass accretion rate can be significantly
modulated by radial epicyclic motions that do not result in dissipation, and
therefore do not drive luminosity fluctuations. The other part of this contrast
is due to the inward decrease of the characteristic inflow time, which leads to
decreasing radial coherence length with increasing fluctuation frequency.Comment: Accepted for publication in ApJ, 35 pages, 11 figures (8 color and 3
greyscale), AASTEX. High-resolution versions can be found at the following
links: [PS] http://www.pha.jhu.edu/~scn/papers/grmhd_var.ps [PDF]
http://www.pha.jhu.edu/~scn/papers/grmhd_var.pd
X-ray vs. Optical Variations in the Seyfert 1 Nucleus NGC 3516: A Puzzling Disconnectedness
We present optical broadband (B and R) observations of the Seyfert 1 nucleus
NGC 3516, obtained at Wise Observatory from March 1997 to March 2002,
contemporaneously with X-ray 2-10 keV measurements with RXTE. With these data
we increase the temporal baseline of this dataset to 5 years, more than triple
to the coverage we have previously presented for this object. Analysis of the
new data does not confirm the 100-day lag of X-ray behind optical variations,
tentatively reported in our previous work. Indeed, excluding the first year's
data, which drive the previous result, there is no significant correlation at
any lag between the X-ray and optical bands. We also find no correlation at any
lag between optical flux and various X-ray hardness ratios. We conclude that
the close relation observed between the bands during the first year of our
program was either a fluke, or perhaps the result of the exceptionally bright
state of NGC 3516 in 1997, to which it has yet to return. Reviewing the results
of published joint X-ray and UV/optical Seyfert monitoring programs, we
speculate that there are at least two components or mechanisms contributing to
the X-ray continuum emission up to 10 keV: a soft component that is correlated
with UV/optical variations on timescales >1 day, and whose presence can be
detected when the source is observed at low enough energies (about 1 keV), is
unabsorbed, or is in a sufficiently bright phase; and a hard component whose
variations are uncorrelated with the UV/optical.Comment: 9 pages, AJ, in pres
Constitutional Venue
A foundational concept of American jurisprudence is the principle that it is unfair to allow litigants to be haled into far away tribunals when the litigants and the litigation have little or nothing to do with the location of such courts. Historically, both personal jurisdiction and venue each served this purpose in related, but distinct ways. Personal jurisdiction is, at base, a limit on the authority of the sovereign. Venue, in contrast, aims to protect parties from being forced to litigate in a location where they would be unfairly disadvantaged. The constitutional boundaries of these early principles came to be tested in the first half of the twentieth century, as the rise of interstate commerce, transportation, and communication technologies prompted states to reach beyond their borders by expanding the jurisdictional limits of their courts through now familiar long-arm statutes. In International Shoe Co. v.Washington, the Court situated the due process inquiry related to a fair location for trial in the personal jurisdiction doctrine—and thus relegated venue to its current subconstitutional status. Forcing the square peg of venue interests into the round hole of personal jurisdiction was, on a theoretical level, an odd choice from the outset. This theoretical foible has plagued the Court’s personal jurisdiction jurisprudence ever since. As a result, the Court’s personal jurisdiction cases are marked by fractured decisions with dueling opinions that articulate conflicting visions of the nature of the due process inquiry in personal jurisdiction analysis. Some Justices minimize the fairness inquiry because they are unable to reconcile the dissonance of individual rights considerations with the origins and core of personal jurisdiction. Other Justices elevate the fairness inquiry to the fore, as they see individual rights protection as critical to the due process analysis. Reconceptualizing the due process fair location inquiry as venue acknowledges the validity of both positions. Fairness in location has little to do with jurisdiction and everything to do with due process and venue. Recognition of the constitutional aspects of venue brings clarity to the Supreme Court’s muddled personal jurisdiction case law. In addition, constitutional venue would provide a basic measure of due process in a small but significant category of cases—most notably detained deportation proceedings—where defendants are prejudiced when they must defend themselves in gravely unfair locations because of the firmly established but deeply flawed conception of venue as lacking constitutional content
A high-density relativistic reflection origin for the soft and hard X-ray excess emission from Mrk 1044
We present the first results from a detailed spectral-timing analysis of a
long (130 ks) XMM-Newton observation and quasi-simultaneous NuSTAR and
Swift observations of the highly-accreting narrow-line Seyfert 1 galaxy Mrk
1044. The broadband (0.350 keV) spectrum reveals the presence of a strong
soft X-ray excess emission below 1.5 keV, iron K emission
complex at 67 keV and a `Compton hump' at 1530 keV. We find
that the relativistic reflection from a high-density accretion disc with a
broken power-law emissivity profile can simultaneously explain the soft X-ray
excess, highly ionized broad iron line and the Compton hump. At low frequencies
( Hz), the power-law continuum dominated 1.55 keV band
lags behind the reflection dominated 0.31 keV band, which is explained with
a combination of propagation fluctuation and Comptonization processes, while at
higher frequencies ( Hz), we detect a soft lag which is
interpreted as a signature of X-ray reverberation from the accretion disc. The
fractional root-mean-squared (rms) variability of the source decreases with
energy and is well described by two variable components: a less variable
relativistic disc reflection and a more variable direct coronal emission. Our
combined spectral-timing analyses suggest that the observed broadband X-ray
variability of Mrk~1044 is mainly driven by variations in the location or
geometry of the optically thin, hot corona.Comment: 23 pages, 19 figures, 4 tables, Published in MNRA
Long-Term X-ray Spectral Variability in Seyfert 1 Galaxies
Direct time-resolved spectral fitting has been performed on continuous RXTE
monitoring of seven Seyfert 1 galaxies in order to study their broadband
spectral variability and Fe K alpha variability characteristics on time scales
of days to years. Variability in the Fe K alpha line is not detected in some
objects but is present in others, e.g., in NGC 3516, NGC 4151 and NGC 5548
there are systematic decreases in line flux by factors of ~2-5 over 3-4 years.
The Fe K alpha line varies less strongly than the broadband continuum, but,
like the continuum, exhibits stronger variability towards longer time scales.
Relatively less model-dependent broadband fractional variability amplitude
(Fvar) spectra also show weaker line variability compared to the continuum
variability. Comparable systematic long-term decreases in the line and
continuum are present in NGC 5548. Overall, however, there is no evidence for
correlated variability between the line and continuum, severely challenging
models in which the line tracks continuum variations modified only by a
light-travel time delay. Local effects such as the formation of an ionized skin
at the site of line emission may be relevant. The spectral fitting and Fvar
spectra both support spectral softening as continuum flux increases.Comment: Accepted for publication in ApJ. 29 page
Multiscaled Cross-Correlation Dynamics in Financial Time-Series
The cross correlation matrix between equities comprises multiple interactions
between traders with varying strategies and time horizons. In this paper, we
use the Maximum Overlap Discrete Wavelet Transform to calculate correlation
matrices over different timescales and then explore the eigenvalue spectrum
over sliding time windows. The dynamics of the eigenvalue spectrum at different
times and scales provides insight into the interactions between the numerous
constituents involved.
Eigenvalue dynamics are examined for both medium and high-frequency equity
returns, with the associated correlation structure shown to be dependent on
both time and scale. Additionally, the Epps effect is established using this
multivariate method and analyzed at longer scales than previously studied. A
partition of the eigenvalue time-series demonstrates, at very short scales, the
emergence of negative returns when the largest eigenvalue is greatest. Finally,
a portfolio optimization shows the importance of timescale information in the
context of risk management
Investigating source confusion in PMN J16034904
PMN J16034904 is a likely member of the rare class of -ray
emitting young radio galaxies. Only one other source, PKS 1718649, has been
confirmed so far. These objects, which may transition into larger radio
galaxies, are a stepping stone to understanding AGN evolution. It is not
completely clear how these young galaxies, seen edge-on, can produce
high-energy -rays. PMN J16034904 has been detected by TANAMI Very
Long Baseline Interferometry (VLBI) observations and has been followed-up with
multiwavelength observations. A Fermi/LAT -ray source has been
associated with it in the LAT catalogs. We have obtained Chandra observations
of the source in order to consider the possibility of source confusion, due to
the relatively large positional uncertainty of Fermi/LAT. The goal was to
investigate the possibility of other X-ray bright sources in the vicinity of
PMN J16034904 that could be counterparts to the -ray emission. With
Chandra/ACIS, we find no other sources in the uncertainty ellipse of Fermi/LAT
data, which includes an improved localization analysis of 8 years of data. We
further study the X-ray fluxes and spectra. We conclude that PMN J16034904
is indeed the second confirmed -ray bright young radio galaxy.Comment: 4 pages, 3 figures, accepted for publication in A&
The Suzaku Observation of NGC 3516: Complex Absorption and the Broad and Narrow Fe K Lines
We present results from a 150 ksec Suzaku observation of the Seyfert 1.5 NGC
3516 in October 2005. The source was in a relatively highly absorbed state. Our
best-fit model is consistent with the presence of a low-ionization absorber
which has a column density near 5 * 10^{22} cm^{-2} and covers most of the
X-ray continuum source (covering fraction 96-100%). A high-ionization absorbing
component, which yields a narrow absorption feature consistent with Fe K XXVI,
is confirmed. A relativistically broadened Fe K alpha line is required in all
fits, even after the complex absorption is taken into account; an additional
partial-covering component is an inadequate substitute for the continuum
curvature associated with the broad Fe line. A narrow Fe K alpha emission line
has a velocity width consistent with the Broad Line Region. The low-ionization
absorber may be responsible for producing the narrow Fe K alpha line, though a
contribution from additional material out of the line of sight is possible. We
include in our model soft band emission lines from He- and H-like ions of N, O,
Ne and Mg, consistent with photo-ionization, though a small contribution from
collisionally-ionized emission is possible.Comment: Accepted for publication in PASJ (Suzaku second special issue). 36
pages, 10 figure
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