194 research outputs found
Pseudo-Dipole Signal Removal from WMAP Data
It is discovered in our previous work that different observational
systematics, e.g., errors of antenna pointing directions, asynchronous between
the attitude and science data, can generate pseudo-dipole signal in full-sky
maps of the cosmic microwave background (CMB) anisotropy published by The
Wilkinson Microwave Anisotropy Probe (WMAP) team. Now the antenna sidelobe
response to the Doppler signal is found to be able to produce similar effect as
well. In this work, independent to the sources, we uniformly model the
pseudo-dipole signal and remove it from published WMAP7 CMB maps by model
fitting. The result demonstrates that most of the released WMAP CMB quadrupole
is artificial.Comment: V3: using WMAP7 dat
Detection of new point-sources in WMAP Cosmic Microwave Background (CMB) maps at high Galactic latitude. A new technique to extract point sources from CMB maps
In experimental microwave maps, point-sources can strongly affect the
estimation of the power-spectrum and/or the test of Gaussianity of the Cosmic
Microwave Background (CMB) component. As a consequence, their removal from the
sky maps represents a critical step in the analysis of the CMB data. Before
removing a source, however, it is necessary to detect it and source extraction
consists of a delicate preliminary operation. In the literature, various
techniques have been presented to detect point-sources in the sky maps. The
most sophisticated ones exploit the multi-frequency nature of the observations
that is typical of the CMB experiments. These techniques have "optimal"
theoretical properties and, at least in principle, are capable of remarkable
performances. Actually, they are rather difficult to use and this deteriorates
the quality of the obtainable results. In this paper, we present a new
technique, the "weighted matched filter" (WMF), that is quite simple to use and
hence more robust in practical applications. Such technique shows particular
efficiency in the detection of sources whose spectra have a slope different
from zero. We apply this method to three Southern Hemisphere sky regions - each
with an area of 400 square degrees - of the seven years Wilkinson Microwave
Anisotropy Probe (WMAP) maps and compare the resulting sources with those of
the two seven-year WMAP point-sources catalogues. In these selected regions we
find seven additional sources not previously listed in WMAP catalogues and
discuss their most likely identification and spectral properties.Comment: Astronomy and Astrophysics, 2011, in pres
Sky maps without anisotropies in the cosmic microwave background are a better fit to WMAP's uncalibrated time ordered data than the official sky maps
The purpose of this reanalysis of the WMAP uncalibrated time ordered data
(TOD) was two fold. The first was to reassess the reliability of the detection
of the anisotropies in the official WMAP sky maps of the cosmic microwave
background (CMB). The second was to assess the performance of a proposed
criterion in avoiding systematic error in detecting a signal of interest. The
criterion was implemented by testing the null hypothesis that the uncalibrated
TOD was consistent with no anisotropies when WMAP's hourly calibration
parameters were allowed to vary. It was shown independently for all 20 WMAP
channels that sky maps with no anisotropies were a better fit to the TOD than
those from the official analysis. The recently launched Planck satellite should
help sort out this perplexing result.Comment: 11 pages with 1 figure and 2 tables. Extensively rewritten to explain
the research bette
Formation of the planet around the millisecond pulsar J1719-1438
Context. Recently the discovery of PSR J1719-1438, a 5.8 ms pulsar with a
companion in a 2.2 hr orbit, was reported. The combination of this orbital
period and the very low mass function is unique. The discoverers, Bailes et
al., proposed an ultracompact X-ray binary (UCXB) as the progenitor system.
However, the standard UCXB scenario would not produce this system as the time
required to reach this orbital period exceeds the current estimate of the age
of the Universe. The detached state of the system aggravates the problem. Aims.
We want to understand the evolutionary history of PSR J1719-1438, and determine
under which circumstances it could have evolved from an UCXB. Methods. We model
UCXB evolution varying the donor size and investigate the effect of a wind mass
loss from the donor, and compare the results with the observed characteristics
of PSR J1719-1438. Results. An UCXB can reach a 2.2 hr orbit within the age of
the Universe, provided that 1) the millisecond pulsar can significantly heat
and expand the donor by pulsar irradiation, or 2) the system loses extra
orbital angular momentum, e.g. via a fast wind from the donor. Conclusions. The
most likely scenario for the formation of PSR J1719-1438 is UCXB evolution
driven by angular momentum loss via the usual gravitational wave emission,
which is enhanced by angular momentum loss via a donor wind of ~3x10^-13
Msun/yr. Depending on the size of the donor during the evolution, the companion
presently probably has a mass of ~1-3 Jupiter masses, making it a very low mass
white dwarf as proposed by Bailes et al. Its composition can be either helium
or carbon-oxygen. A helium white dwarf companion makes the long (for an UCXB)
orbital period easier to explain, but the required inclination makes it a
priori less likely than a carbon-oxygen white dwarf.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysics. v2: Updated a referenc
Degree of randomness: numerical experiments for astrophysical signals
Astrophysical and cosmological signals such as the cosmic microwave
background radiation, as observed, typically contain contributions of different
components, and their statistical properties can be used to distinguish one
from the other. A method developed originally by Kolmogorov is involved for the
study of astrophysical signals of randomness of various degrees. Numerical
performed experiments based on the universality of Kolmogorov distribution and
using a single scaling of the ratio of stochastic to regular components, reveal
basic features in the behavior of generated signals also in terms of a critical
value for that ratio, thus enable the application of this technique for various
observational datasetsComment: 6 pages, 9 figures; Europhys.Letters; to match the published versio
Kolmogorov analysis detecting radio and Fermi gamma-ray sources in cosmic microwave background maps
The Kolmogorov stochasticity parameter is shown to act as a tool to detect
point sources in the cosmic microwave background (CMB) radiation temperature
maps. Kolmogorov CMB map constructed for the WMAP's 7-year datasets reveals
tiny structures which in part coincide with point radio and Fermi/LAT gamma-ray
sources. In the first application of this method, we identified several sources
not present in the then available 0FGL Fermi catalog. Subsequently they were
confirmed in the more recent and more complete 1FGL catalog, thus strengthening
the evidence for the power of this methodology.Comment: 4 pages, 3 figs, 1 Table; to match the published versio
An Absolute Measurement of the Cosmic Microwave Background Radiation Temperature at 10.7 GHz
A balloon-borne experiment has measured the absolute temperature of the
cosmic microwave background radiation (CMBR) at 10.7 GHz to be Tcmbr = 2.730 +-
.014 K. The error is the quadratic sum of several systematic errors, with
statistical error of less than 0.1 mK. The instrument comprises a cooled
corrugated horn antenna coupled to a total-power radiometer. A cryogenic
mechanical waveguide switch alternately connects the radiometer to the horn and
to an internal reference load. The small measured temperature difference (<= 20
mK) between the sky signal and the reference load in conjunction with the use
of a cold front end keeps systematic instrumental corrections small.
Atmospheric and window emission are minimized by flying the instrument at 24 km
altitude. A large outer ground screen and smaller inner screen shield the
instrument from stray radiation from the ground and the balloon. In-flight
tests constrain the magnitude of ground radiation contamination, and low level
interference is monitored through observations in several narrow frequency
bands.Comment: 14 pages, 1 figure, submitted to ApJ
Light Sneutrino Dark Matter at the LHC
In supersymmetric (SUSY) models with Dirac neutrino masses, a weak-scale
trilinear A-term that is not proportional to the small neutrino Yukawa
couplings can induce a sizable mixing between left and right-handed sneutrinos.
The lighter sneutrino mass eigenstate can hence become the lightest SUSY
particle (LSP) and a viable dark matter candidate. In particular, it can be an
excellent candidate for light dark matter with mass below ~10 GeV. Such a light
mixed sneutrino LSP has a dramatic effect on SUSY signatures at the LHC, as
charginos decay dominantly into the light sneutrino plus a charged lepton, and
neutralinos decay invisibly to a neutrino plus a sneutrino. We perform a
detailed study of the LHC potential to resolve the light sneutrino dark matter
scenario by means of three representative benchmark points with different
gluino and squark mass hierarchies. We study in particular the determination of
the LSP (sneutrino) mass from cascade decays involving charginos, using the mT2
variable. Moreover, we address measurements of additional invisible sparticles,
in our case the lightest neutralino, and the question of discrimination against
the MSSM.Comment: 25 pages, 16 figure
Linearization of homogeneous, nearly-isotropic cosmological models
Homogeneous, nearly-isotropic Bianchi cosmological models are considered.
Their time evolution is expressed as a complete set of non-interacting linear
modes on top of a Friedmann-Robertson-Walker background model. This connects
the extensive literature on Bianchi models with the more commonly-adopted
perturbation approach to general relativistic cosmological evolution.
Expressions for the relevant metric perturbations in familiar coordinate
systems can be extracted straightforwardly. Amongst other possibilities, this
allows for future analysis of anisotropic matter sources in a more general
geometry than usually attempted.
We discuss the geometric mechanisms by which maximal symmetry is broken in
the context of these models, shedding light on the origin of different Bianchi
types. When all relevant length-scales are super-horizon, the simplest Bianchi
I models emerge (in which anisotropic quantities appear parallel transported).
Finally we highlight the existence of arbitrarily long near-isotropic epochs
in models of general Bianchi type (including those without an exact isotropic
limit).Comment: 31 pages, 2 figures. Submitted to CQ
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