1,136 research outputs found
SZ and CMB reconstruction using Generalized Morphological Component Analysis
In the last decade, the study of cosmic microwave background (CMB) data has
become one of the most powerful tools to study and understand the Universe.
More precisely, measuring the CMB power spectrum leads to the estimation of
most cosmological parameters. Nevertheless, accessing such precious physical
information requires extracting several different astrophysical components from
the data. Recovering those astrophysical sources (CMB, Sunyaev-Zel'dovich
clusters, galactic dust) thus amounts to a component separation problem which
has already led to an intense activity in the field of CMB studies. In this
paper, we introduce a new sparsity-based component separation method coined
Generalized Morphological Component Analysis (GMCA). The GMCA approach is
formulated in a Bayesian maximum a posteriori (MAP) framework. Numerical
results show that this new source recovery technique performs well compared to
state-of-the-art component separation methods already applied to CMB data.Comment: 11 pages - Statistical Methodology - Special Issue on Astrostatistics
- in pres
Detection and discrimination of cosmological non-Gaussian signatures by multi-scale methods
Recent Cosmic Microwave Background (CMB) observations indicate that the
temperature anisotropies arise from quantum fluctuations in the inflationary
scenario. In the simplest inflationary models, the distribution of CMB
temperature fluctuations should be Gaussian. However, non-Gaussian signatures
can be present. They might have different origins and thus different
statistical and morphological characteristics.
In this context and motivated by recent and future CMB experiments, we search
for, and discriminate between, different non-Gaussian signatures. We analyse
simulated maps of three cosmological sources of temperature anisotropies:
Gaussian distributed CMB anisotropies from inflation, temperature fluctuations
from cosmic strings and anisotropies due to the kinetic Sunyaev-Zel'dovich (SZ)
effect both showing a non-Gaussian character. We use different multi-scale
methods, namely, wavelet, ridgelet and curvelet transforms. The sensitivity and
the discriminating power of the methods is evaluated using simulated data sets.
We find that the bi-orthogonal wavelet transform is the most powerful for the
detection of non-Gaussian signatures and that the curvelet and ridgelet
transforms characterise quite precisely and exclusively the cosmic strings.
They allow us thus to detect them in a mixture of CMB + SZ + cosmic strings. We
show that not one method only should be applied to understand non-Gaussianity
but rather a set of different robust and complementary methods should be used.Comment: Accepted for publication in A&A. Paper with high resolution figures
can be found at http://jstarck.free.fr/cmb03.pd
A Catalog of Diffuse X-ray-Emitting Features within 20 pc of Sgr A*: Twenty Pulsar Wind Nebulae?
We present a catalog of 34 diffuse features identified in X-ray images of the
Galactic center taken with the Chandra X-ray Observatory. Several of the
features have been discussed in the literature previously, including 7 that are
associated with a complex of molecular clouds that exhibits fluorescent line
emission, 4 that are superimposed on the supernova remnant Sgr A East, 2 that
are coincident with radio features that are thought to be the shell of another
supernova remnant, and one that is thought to be a pulsar wind nebula only a
few arcseconds in projection from Sgr A*. However, this leaves 20 features that
have not been reported previously. Based on the weakness of iron emission in
their spectra, we propose that most of them are non-thermal. One long, narrow
feature points toward Sgr A*, and so we propose that this feature is a jet of
synchrotron-emitting particles ejected from the supermassive black hole. For
the others, we show that their sizes (0.1-2 pc in length for D=8 kpc), X-ray
luminosities (between 10^32 and 10^34 erg/s, 2-8 keV), and spectra (power laws
with Gamma=1-3) are consistent with those of pulsar wind nebulae. Based on the
star formation rate at the Galactic center, we expect that ~20 pulsars have
formed in the last 300 kyr, and could be producing pulsar wind nebulae. Only
one of the 19 candidate pulsar wind nebulae is securely detected in an archival
radio image of the Galactic center; the remainder have upper limits
corresponding to L_R<la10^31 erg/s. These radio limits do not strongly
constrain their natures, which underscores the need for further multi-
wavelength studies of this unprecedented sample of Galactic X-ray emitting
structures.Comment: 14 pages, 8 figures, 5 in color. Submitted to Ap
Feasibility and performances of compressed-sensing and sparse map-making with Herschel/PACS data
The Herschel Space Observatory of ESA was launched in May 2009 and is in
operation since. From its distant orbit around L2 it needs to transmit a huge
quantity of information through a very limited bandwidth. This is especially
true for the PACS imaging camera which needs to compress its data far more than
what can be achieved with lossless compression. This is currently solved by
including lossy averaging and rounding steps on board. Recently, a new theory
called compressed-sensing emerged from the statistics community. This theory
makes use of the sparsity of natural (or astrophysical) images to optimize the
acquisition scheme of the data needed to estimate those images. Thus, it can
lead to high compression factors.
A previous article by Bobin et al. (2008) showed how the new theory could be
applied to simulated Herschel/PACS data to solve the compression requirement of
the instrument. In this article, we show that compressed-sensing theory can
indeed be successfully applied to actual Herschel/PACS data and give
significant improvements over the standard pipeline. In order to fully use the
redundancy present in the data, we perform full sky map estimation and
decompression at the same time, which cannot be done in most other compression
methods. We also demonstrate that the various artifacts affecting the data
(pink noise, glitches, whose behavior is a priori not well compatible with
compressed-sensing) can be handled as well in this new framework. Finally, we
make a comparison between the methods from the compressed-sensing scheme and
data acquired with the standard compression scheme. We discuss improvements
that can be made on ground for the creation of sky maps from the data.Comment: 11 pages, 6 figures, 5 tables, peer-reviewed articl
Spectral evolution and polarization of variable structures in the pulsar wind nebula of PSR B0540-69.3
We present high spatial resolution optical imaging and polarization
observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula
(PWN) performed with HST, and compare them with X-ray data obtained with the
Chandra X-ray Observatory. We have studied the bright region southwest of the
pulsar where a bright "blob" is seen in 1999. We show that it may be a result
of local energy deposition around 1999, and that the emission from this then
faded away. Polarization data from 2007 show that the polarization properties
show dramatic spatial variations at the 1999 blob position arguing for a local
process. Several other positions along the pulsar-"blob" orientation show
similar changes in polarization, indicating previous recent local energy
depositions. In X-rays, the spectrum steepens away from the "blob" position,
faster orthogonal to the pulsar-"blob" direction than along this axis of
orientation. This could indicate that the pulsar-"blob" orientation is an axis
along where energy in the PWN is mainly injected, and that this is then
mediated to the filaments in the PWN by shocks. We highlight this by
constructing an [S II]-to-[O III]-ratio map. We argue, through modeling, that
the high [S II]/[O III] ratio is not due to time-dependent photoionization
caused by possible rapid Xray emission variations in the "blob" region. We have
also created a multiwavelength energy spectrum for the "blob" position showing
that one can, to within 2sigma, connect the optical and X-ray emission by a
single power law. We obtain best power-law fits for the X-ray spectrum if we
include "extra" oxygen, in addition to the oxygen column density in the
interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen
is most naturally explained by the oxygen-rich ejecta of the supernova remnant.
The oxygen needed likely places the progenitor mass in the 20 - 25 Msun range.Comment: Accepted by MNRAS on December 6th 2010, 18 pages, 15 figures. The
article with full resolution figures is available here
ftp://ftp.astro.su.se/pub/peter/papers/pwn0540_2010_corrected.pd
A catalog of diffuse X-ray-emitting features within 20 pc of Sagittarius A*: Twenty pulsar wind nebulae?
We present a catalog of 34 diffuse features identified in X-ray images of the Galactic center taken with the Chandra X-Ray Observatory. Several of the features have been discussed in the literature previously, including seven that are associated with a complex of molecular clouds that exhibits fluorescent line emission, four that are superimposed on the supernova remnant Sgr A East, two that are coincident with radio features that are thought to be the shell of another supernova remnant, and one that is thought to be a pulsar wind nebula only a few arcseconds in projection from Sgr A*. However, this leaves 20 features that have not been reported previously. On the basis of the weakness of the iron emission in their spectra, we propose that most of them are nonthermal. One long, narrow feature points toward Sgr A*, and so we propose that this feature is a jet of synchrotron-emitting particles ejected from the supermassive black hole. For the others, we show that their sizes (0.1-2 pc in length for D = 8 kpc), X-ray luminosities (between 10^32 and 10^34 erg s^−1; 2-8 keV), and spectra (power laws with Γ = 1-3) are consistent with those of pulsar wind nebulae. On the basis of the star formation rate at the Galactic center, we expect that ~20 pulsars have formed in the last 300 kyr and could be producing pulsar wind nebulae. Only 1 of the 19 candidate pulsar wind nebulae is securely detected in an archival radio image of the Galactic center; the remainder have upper limits corresponding to L_R ≾ 10^31 erg s^−1. These radio limits do not strongly constrain their natures, which underscores the need for further multiwavelength studies of this unprecedented sample of Galactic X-ray-emitting structures
- …