774 research outputs found
Preparation to the CMB PLANCK data analysis, estimation of the contamination due to the galactic polarized emissions
This work is point of the preparation to the analysis of the PLANCK satellite
data. The PLANCK satellite is an ESA mission which has been launched the 14th
of may 2009 and is dedicaced to the measurement of the Cosmic Microwave
Background (CMB) in temperature and polarization. The presence of diffuse
Galactic polarized emissions disturb the measurement of the CMB anisotropies,
in particular in polarization. Therefore a precise knowledge of these emissions
is needed to obtain the level of accuracy required for PLANCK. In this context,
we have developed and implemented a coherent 3D model of the two mains
polarized Galactic emissions : synchrotron and thermal dust. We have compared
these models to preexisting data: the 23 GHz band of the WMAP data, the 353 GHz
Archeops data and the 408 MHz all-sky continuum survey. We extrapolate these
models to the frequencies where the CMB dominates and we are able to estimate
the contribution of polarized foreground emissions to the polarized CMB
emission measured with PLANCK.Comment: Proceeding of the International Workshop on Cosmic Structure and
Evolution - Cosmology2009, September 23-25, 2009 Bielefeld, German
Non-linear metric perturbation enhancement of primordial gravitational waves
We present the evolution of the full set of Einstein equations during
preheating after inflation. We study a generic supersymmetric model of hybrid
inflation, integrating fields and metric fluctuations in a 3-dimensional
lattice. We take initial conditions consistent with Eintein's constraint
equations. The induced preheating of the metric fluctuations is not large
enough to backreact onto the fields, but preheating of the scalar modes does
affect the evolution of vector and tensor modes. In particular, they do enhance
the induced stochastic background of gravitational waves during preheating,
giving an energy density in general an order of magnitude larger than that
obtained by evolving the tensors fluctuations in an homogeneous background
metric. This enhancement can improve the expectations for detection by planned
gravitational waves observatories.Comment: 5 pages, 4 eps figures, matches Phys. Rev. Lett. versio
Bayesian blind component separation for Cosmic Microwave Background observations
We present a technique for the blind separation of components in CMB data.
The method uses a spectral EM algorithm which recovers simultaneously component
templates, their emission law as a function of wavelength, and noise levels. We
test the method on Planck HFI simulated observations featuring 3 astrophysical
components.Comment: 15 pages, 5 figures, to appear in the Proceedings of the MAXENT 2001
international worksho
MACHe3, a prototype for non-baryonic dark matter search: KeV event detection and multicell correlation
Superfluid He3 at ultra-low temperatures (100 microKelvins) is a sensitive
medium for the bolometric detection of particles. MACHe3 (MAtrix of Cells of
Helium 3) is a project for non-baryonic dark matter search using He3 as a
sensitive medium. Simulations made on a high granularity detector show a very
good rejection to background signals. A multicell prototype including 3
bolometers has been developed to allow correlations between the cells for
background event discrimination. One of the cells contains a low activity Co57
source providing conversion electrons of 7.3 and 13.6 keV to confirm the
detection of low energy events. First results on the multicell prototype are
presented. A detection threshold of 1 keV has been achieved. The detection of
low energy conversion electrons coming from the Co57 source is highlighted as
well as the cosmic muon spectrum measurement. The possibility to reject
background events by using the correlation among the cells is demonstrated from
the simultaneous detection of muons in different cells
Asymfast, a method for convolving maps with asymmetric main beams
We describe a fast and accurate method to perform the convolution of a sky
map with a general asymmetric main beam along any given scanning strategy. The
method is based on the decomposition of the beam as a sum of circular
functions, here Gaussians. It can be easily implemented and is much faster than
pixel-by-pixel convolution. In addition, Asymfast can be used to estimate the
effective circularized beam transfer functions of CMB instruments with
non-symmetric main beam. This is shown using realistic simulations and by
comparison to analytical approximations which are available for Gaussian
elliptical beams. Finally, the application of this technique to Archeops data
is also described. Although developped within the framework of Cosmic Microwave
Background observations, our method can be applied to other areas of
astrophysics.Comment: 9 pages, 4 figures, Phys. Rev. D, in pres
Euclid : Estimation of the Impact of Correlated Readout Noise for Flux Measurements with the Euclid NISP Instrument
The Euclid satellite, to be launched by ESA in 2022, will be a major instrument for cosmology for the next decades. Euclid is composed of two instruments: the Visible instrument and the Near Infrared Spectrometer and Photometer (NISP). In this work, we estimate the implications of correlated readout noise in the NISP detectors for the final in-flight flux measurements. Considering the multiple accumulated readout mode, for which the UTR (Up The Ramp) exposure frames are averaged in groups, we derive an analytical expression for the noise covariance matrix between groups in the presence of correlated noise. We also characterize the correlated readout noise properties in the NISP engineering-grade detectors using long dark integrations. For this purpose, we assume a (1/f) (alpha)-like noise model and fit the model parameters to the data, obtaining typical values of sigma = 19.7(-0.8)(+1.1)e(-)Hz(-0.5), f(knee) = (5.2(-1.3)(+1.8) x 10(-3) Hz and alpha = 1.24(-0.21)(+0.26). Furthermore, via realistic simulations and using a maximum likelihood flux estimator we derive the bias between the input flux and the recovered one. We find that using our analytical expression for the covariance matrix of the correlated readout noise we diminish this bias by up to a factor of four with respect to the white noise approximation for the covariance matrix. Finally, we conclude that the final bias on the in-flight NISP flux measurements should still be negligible even in the white readout noise approximation, which is taken as a baseline for the Euclid on-board processing to estimate the on-sky flux.Peer reviewe
NIKEL: Electronics and data acquisition for kilopixels kinetic inductance camera
A prototype of digital frequency multiplexing electronics allowing the real
time monitoring of microwave kinetic inductance detector (MKIDs) arrays for
mm-wave astronomy has been developed. Thanks to the frequency multiplexing, it
can monitor simultaneously 400 pixels over a 500 MHz bandwidth and requires
only two coaxial cables for instrumenting such a large array. The chosen
solution and the performances achieved are presented in this paper.Comment: 21 pages, 14 figure
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