1,800 research outputs found
A close examination of cosmic microwave background mirror-parity after Planck
Previous claims of significant evidence for mirror-parity in the large-scale
cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy
Probe (WMAP) experiment have been recently echoed in the first study of
isotropy and statistics of CMB data from Planck. We revisit these claims with a
careful analysis of the latest data available. We construct statistical
estimators in both harmonic and pixel space, test them on simulated data with
and without mirror-parity symmetry, apply different Galactic masks, and study
the dependence of the results on arbitrary choices of free parameters. We
confirm that the data exhibit evidence for odd mirror-parity at a significance
which reaches as high as ~ 99 per cent C.L., under some circumstances. However,
given the inherent biases in the pixel-based statistic and the dependence of
both pixel and harmonic space statistics on the particular form of Galactic
masking and other a-posteriori choices, we conclude that these results are not
in significant tension with the predictions of the concordance cosmological
model.Comment: 9 pages, 5 figures, minor changes, as published in MNRA
The Kullback-Leibler Divergence as an Estimator of the Statistical Properties of CMB Maps
The identification of unsubtracted foreground residuals in the cosmic
microwave background maps on large scales is of crucial importance for the
analysis of polarization signals. These residuals add a non-Gaussian
contribution to the data. We propose the Kullback-Leibler (KL) divergence as an
effective, non-parametric test on the one-point probability distribution
function of the data. With motivation in information theory, the KL divergence
takes into account the entire range of the distribution and is highly
non-local. We demonstrate its use by analyzing the large scales of the Planck
2013 SMICA temperature fluctuation map and find it consistent with the expected
distribution at a level of 6%. Comparing the results to those obtained using
the more popular Kolmogorov-Smirnov test, we find the two methods to be in
general agreement.Comment: 12 pages, 5 figures, minor change, as published in JCA
Skewness and Kurtosis as Indicators of Non-Gaussianity in Galactic Foreground Maps
Observational cosmology is entering an era in which high precision will be
required in both measurement and data analysis. Accuracy, however, can only be
achieved with a thorough understanding of potential sources of contamination
from foreground effects. Our primary focus will be on non- Gaussian effects in
foregrounds. This issue will be crucial for coming experiments to determine
B-mode polarization. We propose a novel method for investigating a data set in
terms of skewness and kurtosis in locally defined regions that collectively
cover the entire sky. The method is demonstrated on two sky maps: (i) the SMICA
map of Cosmic Microwave Background fluctuations provided by the Planck
Collaboration and (ii) a version of the Haslam map at 408 MHz that describes
synchrotron radiation. We find that skewness and kurtosis can be evaluated in
combination to reveal local physical information. In the present case, we
demonstrate that the local properties of both maps are predominantly Gaussian.
This result was expected for the SMICA map; that it also applies for the Haslam
map is surprising. The approach described here has a generality and flexibility
that should make it useful in a variety of astrophysical and cosmological
contexts.Comment: 15 pages, 7 figures, minor change, as published in JCA
The 43GHz SiO maser in the circumstellar envelope of the AGB star R Cassiopeiae
We present multi-epoch, total intensity, high-resolution images of 43GHz,
v=1, J=1-0 SiO maser emission toward the Mira variable R Cas. In total we have
23 epochs of data for R Cas at approximate monthly intervals over an optical
pulsation phase range from 0.158 to 1.78. These maps show a ring-like
distribution of the maser features in a shell, which is assumed to be centred
on the star at a radius of 1.6 to 2.3 times the stellar radii. It is clear from
these images that the maser emission is significantly extended around the star.
At some epochs a faint outer arc can be seen at 2.2 stellar radii. The
intensity of the emission waxes and wanes during the stellar phase. Some maser
features are seen infalling as well as outflowing. We have made initial
comparisons of our data with models by Gray et. al. (2009).Comment: 12 pages, 14 figure
Stochastic inequalities for single-server loss queueing systems
The present paper provides some new stochastic inequalities for the
characteristics of the and loss queueing systems. These
stochastic inequalities are based on substantially deepen up- and
down-crossings analysis, and they are stronger than the known stochastic
inequalities obtained earlier. Specifically, for a class of queueing
system, two-side stochastic inequalities are obtained.Comment: 17 pages, 11pt To appear in Stochastic Analysis and Application
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