3,405 research outputs found
High Energy Variability Of Synchrotron-Self Compton Emitting Sources: Why One Zone Models Do Not Work And How We Can Fix It
With the anticipated launch of GLAST, the existing X-ray telescopes, and the
enhanced capabilities of the new generation of TeV telescopes, developing tools
for modeling the variability of high energy sources such as blazars is becoming
a high priority. We point out the serious, innate problems one zone
synchrotron-self Compton models have in simulating high energy variability. We
then present the first steps toward a multi zone model where non-local, time
delayed Synchrotron-self Compton electron energy losses are taken into account.
By introducing only one additional parameter, the length of the system, our
code can simulate variability properly at Compton dominated stages, a situation
typical of flaring systems. As a first application, we were able to reproduce
variability similar to that observed in the case of the puzzling `orphan' TeV
flares that are not accompanied by a corresponding X-ray flare.Comment: to appear in the 1st GLAST symposium proceeding
The Utility of Trouble: Maximizing the Value of Our Human Services Dollars
Outlines recommendations to standardize service delivery areas and consolidate area offices of the state's seven largest human services agencies, as well as to close antiquated institutions. Projects benefits such as improved accessibility and savings
Frequentist and Bayesian measures of confidence via multiscale bootstrap for testing three regions
A new computation method of frequentist -values and Bayesian posterior
probabilities based on the bootstrap probability is discussed for the
multivariate normal model with unknown expectation parameter vector. The null
hypothesis is represented as an arbitrary-shaped region. We introduce new
parametric models for the scaling-law of bootstrap probability so that the
multiscale bootstrap method, which was designed for one-sided test, can also
computes confidence measures of two-sided test, extending applicability to a
wider class of hypotheses. Parameter estimation is improved by the two-step
multiscale bootstrap and also by including higher-order terms. Model selection
is important not only as a motivating application of our method, but also as an
essential ingredient in the method. A compromise between frequentist and
Bayesian is attempted by showing that the Bayesian posterior probability with
an noninformative prior is interpreted as a frequentist -value of
``zero-sided'' test
Physical mechanisms may be as important as brain mechanisms in evolution of speech [Commentary on Ackerman, Hage, & Ziegler. Brain Mechanisms of acoustic communication in humans and nonhuman primates: an evolutionary perspective]
We present two arguments why physical adaptations for vocalization may be as important as neural adaptations. First, fine control over vocalization is not easy for physical reasons, and modern humans may be exceptional. Second, we present an example of a gorilla that shows rudimentary voluntary control over vocalization, indicating that some neural control is already shared with great apes
Discovery of a very X-ray luminous galaxy cluster at z=0.89 in the WARPS survey
We report the discovery of the galaxy cluster ClJ1226.9+3332 in the Wide
Angle ROSAT Pointed Survey (WARPS). At z=0.888 and L_X=1.1e45 erg/s (0.5-2.0
keV, h_0=0.5) ClJ1226.9+3332 is the most distant X-ray luminous cluster
currently known. The mere existence of this system represents a huge problem
for Omega_0=1 world models.
At the modest (off-axis) resolution of the ROSAT PSPC observation in which
the system was detected, ClJ1226.9+3332 appears relaxed; an off-axis HRI
observation confirms this impression and rules out significant contamination
from point sources. However, in moderately deep optical images (R and I band)
the cluster exhibits signs of substructure in its apparent galaxy distribution.
A first crude estimate of the velocity dispersion of the cluster galaxies based
on six redshifts yields a high value of 1650 km/s, indicative of a very massive
cluster and/or the presence of substructure along the line of sight. While a
more accurate assessment of the dynamical state of this system requires much
better data at both optical and X-ray wavelengths, the high mass of the cluster
has already been unambiguously confirmed by a very strong detection of the
Sunyaev-Zel'dovich effect in its direction (Joy et al. 2001).
Using ClJ1226.9+3332 and ClJ0152.7-1357 (z=0.835), the second-most distant
X-ray luminous cluster currently known and also a WARPS discovery, we obtain a
first estimate of the cluster X-ray luminosity function at 0.8<z<1.4 and
L_X>5e44 erg/s. Using the best currently available data, we find the comoving
space density of very distant, massive clusters to be in excellent agreement
with the value measured locally (z<0.3), and conclude that negative evolution
is not required at these luminosities out to z~1. (truncated)Comment: accepted for publication in ApJ Letters, 6 pages, 2 figures, uses
emulateapj.st
Month-Timescale Optical Variability in the M87 Jet
A previously inconspicuous knot in the M87 jet has undergone a dramatic
outburst and now exceeds the nucleus in optical and X-ray luminosity.
Monitoring of M87 with the Hubble Space Telescope and Chandra X-ray Observatory
during 2002-2003, has found month-timescale optical variability in both the
nucleus and HST-1, a knot in the jet 0.82'' from the nucleus. We discuss the
behavior of the variability timescales as well as spectral energy distribution
of both components. In the nucleus, we see nearly energy-independent
variability behavior. Knot HST-1, however, displays weak energy dependence in
both X-ray and optical bands, but with nearly comparable rise/decay timescales
at 220 nm and 0.5 keV. The flaring region of HST-1 appears stationary over
eight months of monitoring. We consider various emission models to explain the
variability of both components. The flares we see are similar to those seen in
blazars, albeit on longer timescales, and so could, if viewed at smaller
angles, explain the extreme variability properties of those objects.Comment: 4 pages, 3 figures, ApJ Lett., in pres
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