88 research outputs found
Variable-delay Polarization Modulators for Cryogenic Millimeter-wave Applications
We describe the design, construction, and initial validation of the
variable-delay polarization modulator (VPM) designed for the PIPER cosmic
microwave background polarimeter. The VPM modulates between linear and circular
polarization by introducing a variable phase delay between orthogonal linear
polarizations. Each VPM has a diameter of 39 cm and is engineered to operate in
a cryogenic environment (1.5 K). We describe the mechanical design and
performance of the kinematic double-blade flexure and drive mechanism along
with the construction of the high precision wire grid polarizers.Comment: 8 pages, 10 Figures, Submitted to Review of Scientific Instrument
CMB E/B decomposition of incomplete sky: a pixel space approach
CMB polarization signal may be decomposed into gradient-like (E) and
curl-like (B) mode. We have investigated E/B decomposition in pixel space. We
find E/B mixing due to incomplete sky is localized in pixel-space, and
negligible in the regions far away from the masked area. By estimating the
expected local leakage power, we have diagnosed ambiguous pixels. Our criteria
for ambiguous pixels (i.e. r_c) is associated with the tensor-to-scalar ratio
of B mode power spectrum, which the leakage power is comparable to. By setting
r_c to a lower value, we may reduce leakage level, but reduce sky fraction at
the same time. Therefore, we have solved \partial \Delta C_l/\partial r_c=0,
and obtained the optimal r_c, which minimizes the estimation uncertainty, given
a foreground mask and noise level. We have applied our method to a simulated
map blocked by a foreground (diffuse + point source) mask. Our simulation shows
leakage power is smaller than primordial (i.e. unlensed) B mode power spectrum
of tensor-to-scalar ratio r\sim 10^{-3} at wide range of multipoles (50\lesssim
l \lesssim 2000), while allowing us to retain sky fraction ~ 0.48.Comment: v2: the point of the method strengthened, v3: criteria for ambiguous
pixels rigorously derived, v4: matched with the accepted version in A&A
(minor change), v5: typos correcte
Second and third season QUaD CMB temperature and polarization power spectra
We report results from the second and third seasons of observation with the
QUaD experiment. Angular power spectra of the Cosmic Microwave Background are
derived for both temperature and polarization at both 100 GHz and 150 GHz, and
as cross frequency spectra. All spectra are subjected to an extensive set of
jackknife tests to probe for possible systematic contamination. For the
implemented data cuts and processing technique such contamination is
undetectable. We analyze the difference map formed between the 100 and 150 GHz
bands and find no evidence of foreground contamination in polarization. The
spectra are then combined to form a single set of results which are shown to be
consistent with the prevailing LCDM model. The sensitivity of the polarization
results is considerably better than that of any previous experiment -- for the
first time multiple acoustic peaks are detected in the E-mode power spectrum at
high significance.Comment: 24 pages, 23 figures, updated to reflect published versio
QUaD: A High-Resolution Cosmic Microwave Background Polarimeter
We describe the QUaD experiment, a millimeter-wavelength polarimeter designed
to observe the Cosmic Microwave Background (CMB) from a site at the South Pole.
The experiment comprises a 2.64 m Cassegrain telescope equipped with a
cryogenically cooled receiver containing an array of 62 polarization-sensitive
bolometers. The focal plane contains pixels at two different frequency bands,
100 GHz and 150 GHz, with angular resolutions of 5 arcmin and 3.5 arcmin,
respectively. The high angular resolution allows observation of CMB temperature
and polarization anisotropies over a wide range of scales. The instrument
commenced operation in early 2005 and collected science data during three
successive Austral winter seasons of observation.Comment: 23 pages, author list and text updated to reflect published versio
First season QUaD CMB temperature and polarization power spectra
QUaD is a bolometric CMB polarimeter sited at the South Pole, operating at frequencies of 100 and 150 GHz. In this paper we report preliminary results from the first season of operation (austral winter 2005). All six CMB power spectra are presented derived as cross spectra between the 100 and 150 GHz maps using 67 days of observation in a low foreground region of approximately 60 deg^2. These data are a small fraction of the data acquired to date. The measured spectra are consistent with the ΛCDM cosmological model. We perform jackknife tests that indicate that the observed signal has negligible contamination from instrumental systematics. In addition, by using a frequency jackknife we find no evidence for foreground contamination
Characterization of the Millimeter-Wave Polarization of Centaurus A with QUaD
Centaurus (Cen) A represents one of the best candidates for an isolated,
compact, highly polarized source that is bright at typical cosmic microwave
background (CMB) experiment frequencies. We present measurements of the 4
degree by 2 degree region centered on Cen A with QUaD, a CMB polarimeter whose
absolute polarization angle is known to 0.5 degrees. Simulations are performed
to assess the effect of misestimation of the instrumental parameters on the
final measurement and systematic errors due to the field's background structure
and temporal variability from Cen A's nuclear region are determined. The total
(Q, U) of the inner lobe region is (1.00 +/- 0.07 (stat.) +/- 0.04 (sys.),
-1.72 +/- 0.06 +/- 0.05) Jy at 100 GHz and (0.80 +/- 0.06 +/- 0.06, -1.40 +/-
0.07 +/- 0.08) Jy at 150 GHz, leading to polarization angles and total errors
of -30.0 +/- 1.1 degrees and -29.1 +/- 1.7 degrees. These measurements will
allow the use of Cen A as a polarized calibration source for future millimeter
experiments.Comment: 9 pages, 8 figures, v2 matches version published in Ap
The Primordial Inflation Polarization Explorer (PIPER)
The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne
cosmic microwave background (CMB) polarimeter designed to search for evidence
of inflation by measuring the large-angular scale CMB polarization signal.
BICEP2 recently reported a detection of B-mode power corresponding to the
tensor-to-scalar ratio r = 0.2 on ~2 degree scales. If the BICEP2 signal is
caused by inflationary gravitational waves (IGWs), then there should be a
corresponding increase in B-mode power on angular scales larger than 18
degrees. PIPER is currently the only suborbital instrument capable of fully
testing and extending the BICEP2 results by measuring the B-mode power spectrum
on angular scales = ~0.6 deg to 90 deg, covering both the reionization
bump and recombination peak, with sensitivity to measure the tensor-to-scalar
ratio down to r = 0.007, and four frequency bands to distinguish foregrounds.
PIPER will accomplish this by mapping 85% of the sky in four frequency bands
(200, 270, 350, 600 GHz) over a series of 8 conventional balloon flights from
the northern and southern hemispheres. The instrument has background-limited
sensitivity provided by fully cryogenic (1.5 K) optics focusing the sky signal
onto four 32x40-pixel arrays of time-domain multiplexed Transition-Edge Sensor
(TES) bolometers held at 140 mK. Polarization sensitivity and systematic
control are provided by front-end Variable-delay Polarization Modulators
(VPMs), which rapidly modulate only the polarized sky signal at 3 Hz and allow
PIPER to instantaneously measure the full Stokes vector (I, Q, U, V) for each
pointing. We describe the PIPER instrument and progress towards its first
flight.Comment: 11 pages, 7 figures. To be published in Proceedings of SPIE Volume
9153. Presented at SPIE Astronomical Telescopes + Instrumentation 2014,
conference 915
Fabrication of an Antenna-Coupled Bolometer for Cosmic Microwave Background Polarimetry
We describe the development of a detector for precise measurements of the cosmic microwave background polarization. The detector employs a waveguide to couple light between a pair of Mo/Au superconducting transition edge sensors (TES) and a feedhorn. Incorporation of an on-chip ortho-mode transducer (OMT) results in high isolation. The OMT is micromachined and bonded to the microstrip and TES circuits in a low temperature wafer bonding process. The wafer bonding process incorporates a buried superconducting niobium layer with a single crystal silicon layer which serves as the leg isolated TES membrane and as the microstrip dielectric. We describe the micromachining and wafer bonding process and report measurement results of the microwave circuitry operating in the 29-43GHz band along with Johnson noise measurements of the TES membrane structures and development of Mo/Au TES operating under '00mK
Probing the last scattering surface through the recent and future CMB observations
We have constrained the extended (delayed and accelerated) models of hydrogen
recombination, by investigating associated changes of the position and the
width of the last scattering surface. Using the recent CMB and SDSS data, we
find that the recent data constraints favor the accelerated recombination
model, though the other models (standard, delayed recombination) are not ruled
out at 1- confidence level. If the accelerated recombination had
actually occurred in our early Universe, baryonic clustering on small-scales is
likely to be the cause of it. By comparing the ionization history of baryonic
cloud models with that of the best-fit accelerated recombination model, we find
that some portion of our early Universe has baryonic underdensity. We have made
the forecast on the PLANCK data constraint, which shows that we will be able to
rule out the standard or delayed recombination models, if the recombination in
our early Universe had proceeded with or lower, and
residual foregrounds and systematic effects are negligible.Comment: v2: matched with the accepted version (conclusions unchanged
Scientific optimization of a ground-based CMB polarization experiment
We investigate the science goals achievable with the upcoming generation of
ground-based Cosmic Microwave Background polarization experiments and calculate
the optimal sky coverage for such an experiment including the effects of
foregrounds. We find that with current technology an E-mode measurement will be
sample-limited, while a B-mode measurement will be detector-noise-limited. We
conclude that a 300 sq deg survey is an optimal compromise for a two-year
experiment to measure both E and B-modes, and that ground-based polarization
experiments can make an important contribution to B-mode surveys. Focusing on
one particular experiment, QUaD, a proposed bolometric polarimeter operating
from the South Pole, we find that a ground-based experiment can make a high
significance measurement of the acoustic peaks in the E-mode spectrum, and will
be able to detect the gravitational lensing signal in the B-mode spectrum. Such
an experiment could also directly detect the gravitational wave component of
the B-mode spectrum if the amplitude of the signal is close to current upper
limits. We also investigate how a ground-based experiment can improve
constraints on the cosmological parameters. We estimate that by combining two
years of QUaD data with the four-year WMAP data, an optimized ground-based
polarization experiment can improve constraints on cosmological parameters by a
factor of two. If the foreground contamination can be reduced, the measurement
of the tensor-to-scalar ratio can be improved by up to a factor of six over
that obtainable from WMAP alone.Comment: 17 pages, 11 figures replaced with version accepted by MNRA
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