4,808 research outputs found
The angular power spectrum of radio emission at 2.3 GHz
We have analysed the Rhodes/HartRAO survey at 2326 MHz and derived the global
angular power spectrum of Galactic continuum emission. In order to measure the
angular power spectrum of the diffuse component, point sources were removed
from the map by median filtering. A least-square fit to the angular power
spectrum of the entire survey with a power law spectrum C_l proportional to
l^{-alpha}, gives alpha = 2.43 +/- 0.01 for l = 2-100. The angular power
spectrum of radio emission appears to steepen at high Galactic latitudes and
for observed regions with |b| > 20 deg, the fitted spectral index is alpha =
2.92 +/- 0.07. We have extrapolated this result to 30 GHz (the lowest frequency
channel of Planck) and estimate that no significant contribution to the sky
temperature fluctuation is likely to come from synchrotron at degree-angular
scalesComment: 10 pages, 10 figures, accepted for publication by Astronomy &
Astrophysic
LISA data analysis I: Doppler demodulation
The orbital motion of the Laser Interferometer Space Antenna (LISA) produces
amplitude, phase and frequency modulation of a gravitational wave signal. The
modulations have the effect of spreading a monochromatic gravitational wave
signal across a range of frequencies. The modulations encode useful information
about the source location and orientation, but they also have the deleterious
affect of spreading a signal across a wide bandwidth, thereby reducing the
strength of the signal relative to the instrument noise. We describe a simple
method for removing the dominant, Doppler, component of the signal modulation.
The demodulation reassembles the power from a monochromatic source into a
narrow spike, and provides a quick way to determine the sky locations and
frequencies of the brightest gravitational wave sources.Comment: 5 pages, 7 figures. References and new comments adde
Bayesian Power Spectrum Analysis of the First-Year WMAP data
We present the first results from a Bayesian analysis of the WMAP first year
data using a Gibbs sampling technique. Using two independent, parallel
supercomputer codes we analyze the WMAP Q, V and W bands. The analysis results
in a full probabilistic description of the information the WMAP data set
contains about the power spectrum and the all-sky map of the cosmic microwave
background anisotropies. We present the complete probability distributions for
each C_l including any non-Gaussianities of the power spectrum likelihood.
While we find good overall agreement with the previously published WMAP
spectrum, our analysis uncovers discrepancies in the power spectrum estimates
at low l multipoles. For example we claim the best-fit Lambda-CDM model is
consistent with the C_2 inferred from our combined Q+V+W analysis with a 10%
probability of an even larger theoretical C_2. Based on our exact analysis we
can therefore attribute the "low quadrupole issue" to a statistical
fluctuation.Comment: 5 pages. 4 figures. For additional information and data see
http://www.astro.uiuc.edu/~iodwyer/research#wma
Goodness-of-Fit Tests to study the Gaussianity of the MAXIMA data
Goodness-of-Fit tests, including Smooth ones, are introduced and applied to
detect non-Gaussianity in Cosmic Microwave Background simulations. We study the
power of three different tests: the Shapiro-Francia test (1972), the
uncategorised smooth test developed by Rayner and Best(1990) and the Neyman's
Smooth Goodness-of-fit test for composite hypotheses (Thomas and Pierce 1979).
The Smooth Goodness-of-Fit tests are designed to be sensitive to the presence
of ``smooth'' deviations from a given distribution. We study the power of these
tests based on the discrimination between Gaussian and non-Gaussian
simulations. Non-Gaussian cases are simulated using the Edgeworth expansion and
assuming pixel-to-pixel independence. Results show these tests behave similarly
and are more powerful than tests directly based on cumulants of order 3, 4, 5
and 6. We have applied these tests to the released MAXIMA data. The applied
tests are built to be powerful against detecting deviations from univariate
Gaussianity. The Cholesky matrix corresponding to signal (based on an assumed
cosmological model) plus noise is used to decorrelate the observations previous
to the analysis. Results indicate that the MAXIMA data are compatible with
Gaussianity.Comment: MNRAS, in pres
Non-Gaussian CMBR angular power spectra
In this paper we show how the prediction of CMBR angular power spectra
in non-Gaussian theories is affected by a cosmic covariance problem, that is
correlations impart features on any observed spectrum
which are absent from the average spectrum. Therefore the average
spectrum is rendered a bad observational prediction, and two new prediction
strategies, better adjusted to these theories, are proposed. In one we search
for hidden random indices conditional to which the theory is released from the
correlations. Contact with experiment can then be made in the form of the
conditional power spectra plus the random index distribution. In another
approach we apply to the problem a principal component analysis. We discuss the
effect of correlations on the predictivity of non-Gaussian theories. We finish
by showing how correlations may be crucial in delineating the borderline
between predictions made by non-Gaussian and Gaussian theories. In fact, in
some particular theories, correlations may act as powerful non-Gaussianity
indicators
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