15,829 research outputs found
Systematic errors in cosmic microwave background polarization measurements
We investigate the impact of instrumental systematic errors on the potential
of cosmic microwave background polarization experiments targeting primordial
B-modes. To do so, we introduce spin-weighted Muller matrix-valued fields
describing the linear response of the imperfect optical system and receiver,
and give a careful discussion of the behaviour of the induced systematic
effects under rotation of the instrument. We give the correspondence between
the matrix components and known optical and receiver imperfections, and compare
the likely performance of pseudo-correlation receivers and those that modulate
the polarization with a half-wave plate. The latter is shown to have the
significant advantage of not coupling the total intensity into polarization for
perfect optics, but potential effects like optical distortions that may be
introduced by the quasi-optical wave plate warrant further investigation. A
fast method for tolerancing time-invariant systematic effects is presented,
which propagates errors through to power spectra and cosmological parameters.
The method extends previous studies to an arbitrary scan strategy, and
eliminates the need for time-consuming Monte-Carlo simulations in the early
phases of instrument and survey design. We illustrate the method with both
simple parametrized forms for the systematics and with beams based on
physical-optics simulations. Example results are given in the context of
next-generation experiments targeting tensor-to-scalar ratios r ~ 0.01.Comment: 19 pages, 7 figures; Minor changes to match version accepted by MNRA
EBEX: A balloon-borne CMB polarization experiment
EBEX is a NASA-funded balloon-borne experiment designed to measure the
polarization of the cosmic microwave background (CMB). Observations will be
made using 1432 transition edge sensor (TES) bolometric detectors read out with
frequency multiplexed SQuIDs. EBEX will observe in three frequency bands
centered at 150, 250, and 410 GHz, with 768, 384, and 280 detectors in each
band, respectively. This broad frequency coverage is designed to provide
valuable information about polarized foreground signals from dust. The
polarized sky signals will be modulated with an achromatic half wave plate
(AHWP) rotating on a superconducting magnetic bearing (SMB) and analyzed with a
fixed wire grid polarizer. EBEX will observe a patch covering ~1% of the sky
with 8' resolution, allowing for observation of the angular power spectrum from
\ell = 20 to 1000. This will allow EBEX to search for both the primordial
B-mode signal predicted by inflation and the anticipated lensing B-mode signal.
Calculations to predict EBEX constraints on r using expected noise levels show
that, for a likelihood centered around zero and with negligible foregrounds,
99% of the area falls below r = 0.035. This value increases by a factor of 1.6
after a process of foreground subtraction. This estimate does not include
systematic uncertainties. An engineering flight was launched in June, 2009,
from Ft. Sumner, NM, and the long duration science flight in Antarctica is
planned for 2011. These proceedings describe the EBEX instrument and the North
American engineering flight.Comment: 12 pages, 9 figures, Conference proceedings for SPIE Millimeter,
Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy V
(2010
MAXIPOL: Cosmic Microwave Background Polarimetry Using a Rotating Half-Wave Plate
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure
the E-mode polarization of the cosmic microwave background radiation (CMB).
MAXIPOL is the first bolometric CMB experiment to observe the sky using rapid
polarization modulation. To build MAXIPOL, the CMB temperature anisotropy
experiment MAXIMA was retrofitted with a rotating half-wave plate and a
stationary analyzer. We describe the instrument, the observations, the
calibration and the reduction of data collected with twelve polarimeters
operating at 140 GHz and with a FWHM beam size of 10 arcmin. We present maps of
the Q and U Stokes parameters of an 8 deg^2 region of the sky near the star
Beta Ursae Minoris. The power spectra computed from these maps give weak
evidence for an EE signal. The maximum-likelihood amplitude of
l(l+1)C^{EE}_{l}/(2 pi) is 55_{-45}^{+51} uK^2 (68%), and the likelihood
function is asymmetric and skewed positive such that with a uniform prior the
probability that the amplitude is positive is 96%. This result is consistent
with the expected concordance LCDM amplitude of 14 uK^2. The maximum likelihood
amplitudes for l(l+1)C^{BB}_{l}/(2 pi) and are
-31_{-19}^{+31} and 18_{-34}^{+27} uK^2 (68%), respectively, which are
consistent with zero. All of the results are for one bin in the range 151 < l <
693. Tests revealed no residual systematic errors in the time or map domain. A
comprehensive discussion of the analysis of the data is presented in a
companion paper.Comment: 19 pages, 11 figures, 2 tables, submitted to Ap
A Spin Modulated Telescope to Make Two Dimensional CMB Maps
We describe the HEMT Advanced Cosmic Microwave Explorer (HACME), a balloon
borne experiment designed to measure sub-degree scale Cosmic Microwave
Background anisotropy over hundreds of square degrees, using a unique two
dimensional scanning strategy. A spinning flat mirror that is canted relative
to its spin axis modulates the direction of beam response in a nearly
elliptical path on the sky. The experiment was successfully flown in February
of 1996, achieving near laboratory performance for several hours at float
altitude. A map free of instrumental systematic effects is produced for a 3.5
hour observation of 630 square degrees, resulting in a flat band power upper
limit of (l(l+1)C_l/2 pi)^0.5 < 77 microK at l = 38 (95% confidence). The
experiment design, flight operations and data, including atmospheric effects
and noise performance, are discussed.Comment: 4 pages, 3 figure
CMB power spectrum estimation with non-circular beam and incomplete sky coverage
Over the last decade, measurements of the CMB anisotropy has spearheaded the
remarkable transition of cosmology into a precision science. However,
addressing the systematic effects in the increasingly sensitive, high
resolution, `full' sky measurements from different CMB experiments pose a stiff
challenge. The analysis techniques must not only be computationally fast to
contend with the huge size of the data, but, the higher sensitivity also limits
the simplifying assumptions which can then be invoked to achieve the desired
speed without compromising the final precision goals. While maximum likelihood
is desirable, the enormous computational cost makes the suboptimal method of
power spectrum estimation using Pseudo-C_l unavoidable for high resolution
data. We provide a (semi)analytic framework to estimate bias in the power
spectrum due to the effect of beam non-circularity and non-uniform sky coverage
including incomplete/masked sky maps and scan strategy. The approach is
perturbative in the distortion of the beam from non-circularity, allowing for
rapid computations when the beam is mildly non-circular. We advocate that it is
computationally advantageous to employ `soft' azimuthally apodized masks whose
spherical harmonic transform die down fast with m. We numerically implement our
method for non-rotating beams. We present preliminary estimates of the
computational cost to evaluate the bias for the upcoming CMB anisotropy probes
l_max~3000, with angular resolution comparable to the Planck surveyor mission.
We further show that this implementation and estimate is applicable for
rotating beams on equal declination scans and possibly can be extended to
simple approximations to other scan strategies.Comment: 22 pages, 7 figures. Revised presentation to highlight significance
of extended results. Matches version accepted to the MNRA
Large Radio Telescopes for Anomalous Microwave Emission Observations
We discuss in this paper the problem of the Anomalous Microwave Emission
(AME) in the light of ongoing or future observations to be performed with the
largest fully steerable radio telescope in the world. High angular resolution
observations of the AME will enable astronomers to drastically improve the
knowledge of the AME mechanisms as well as the interplay between the different
constituents of the interstellar medium in our galaxy. Extragalactic
observations of the AME have started as well, and high resolution is even more
important in this kind of observations. When cross-correlating with IR-dust
emission, high angular resolution is also of fundamental importance in order to
obtain unbiased results. The choice of the observational frequency is also of
key importance in continuum observation. We calculate a merit function that
accounts for the signal-to-noise ratio (SNR) in AME observation given the
current state-of-the-art knowledge and technology. We also include in our merit
functions the frequency dependence in the case of multifrequency observations.
We briefly mention and compare the performance of four of the largest
radiotelescopes in the world and hope the observational programs in each of
them will be as intense as possible.Comment: Review accepted for publication in Advances in Astronom
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