54 research outputs found
Measurement of the cosmic microwave background polarization lensing power spectrum from two years of POLARBEAR data
We present a measurement of the gravitational lensing deflection power spectrum reconstructed with two seasons of cosmic microwave background polarization data from the POLARBEAR experiment. Observations were taken at 150 GHz from 2012 to 2014 and surveyed three patches of sky totaling 30 square degrees. We test the consistency of the lensing spectrum with a cold dark matter cosmology and reject the no-lensing hypothesis at a confidence of 10.9σ, including statistical and systematic uncertainties. We observe a value of AL = 1.33 ± 0.32 (statistical) ±0.02 (systematic) ±0.07 (foreground) using all polarization lensing estimators, which corresponds to a 24% accurate measurement of the lensing amplitude. Compared to the analysis of the first- year data, we have improved the breadth of both the suite of null tests and the error terms included in the estimation of systematic contamination
Internal delensing of cosmic microwave background polarization B-Modes with the POLARBEAR experiment
International audienceUsing only cosmic microwave background polarization data from the polarbear experiment, we measure B-mode polarization delensing on subdegree scales at more than 5σ significance. We achieve a 14% B-mode power variance reduction, the highest to date for internal delensing, and improve this result to 22% by applying for the first time an iterative maximum a posteriori delensing method. Our analysis demonstrates the capability of internal delensing as a means of improving constraints on inflationary models, paving the way for the optimal analysis of next-generation primordial B-mode experiments
The Simons Observatory: Characterizing the Large Aperture Telescope Receiver with Radio Holography
We present near-field radio holography measurements of the Simons Observatory
Large Aperture Telescope Receiver optics. These measurements demonstrate that
radio holography of complex millimeter-wave optical systems comprising
cryogenic lenses, filters, and feed horns can provide detailed characterization
of wave propagation before deployment. We used the measured amplitude and
phase, at 4K, of the receiver near-field beam pattern to predict two key
performance parameters: 1) the amount of scattered light that will spill past
the telescope to 300K and 2) the beam pattern expected from the receiver when
fielded on the telescope. These cryogenic measurements informed the removal of
a filter, which led to improved optical efficiency and reduced side-lobes at
the exit of the receiver. Holography measurements of this system suggest that
the spilled power past the telescope mirrors will be less than 1% and the main
beam with its near side-lobes are consistent with the nominal telescope design.
This is the first time such parameters have been confirmed in the lab prior to
deployment of a new receiver. This approach is broadly applicable to millimeter
and sub-millimeter instruments.Comment: in proces
Development of the Low Frequency Telescope Focal Plane Detector Modules for LiteBIRD
LiteBIRD is a JAXA-led strategic large-class satellite mission designed to
measure the polarization of the cosmic microwave background and Galactic
foregrounds from 34 to 448 GHz across the entire sky from L2 in the late 2020s.
The scientific payload includes three telescopes which are called the low-,
mid-, and high-frequency telescopes each with their own receiver that covers a
portion of the mission's frequency range. The low frequency telescope will map
synchrotron radiation from the Galactic foreground and the cosmic microwave
background. We discuss the design, fabrication, and characterization of the
low-frequency focal plane modules for low-frequency telescope, which has a
total bandwidth ranging from 34 to 161 GHz. There will be a total of 4
different pixel types with 8 overlapping bands to cover the full frequency
range. These modules are housed in a single low-frequency focal plane unit
which provides thermal isolation, mechanical support, and radiative baffling
for the detectors. The module design implements multi-chroic lenslet-coupled
sinuous antenna arrays coupled to transition edge sensor bolometers read out
with frequency-domain mulitplexing. While this technology has strong heritage
in ground-based cosmic microwave background experiments, the broad frequency
coverage, low optical loading conditions, and the high cosmic ray background of
the space environment require further development of this technology to be
suitable for LiteBIRD. In these proceedings, we discuss the optical and
bolometeric characterization of a triplexing prototype pixel with bands
centered on 78, 100, and 140 GHz.Comment: SPIE Astronomical Telescope + Instrumentation (AS22
The Simons Observatory: Magnetic Sensitivity Measurements of Microwave SQUID Multiplexers
The Simons Observatory (SO) will be a cosmic microwave background (CMB)
survey experiment with three small-aperture telescopes and one large-aperture
telescope, which will observe from the Atacama Desert in Chile. In total, SO
will field 70,000 transition-edge sensor (TES) bolometers in six spectral
bands centered between 27 and 280 GHz in order to achieve the sensitivity
necessary to measure or constrain numerous cosmological quantities. The SO
Universal Focal Plane Modules (UFMs) each contain a 150 mm diameter TES
detector array, horn or lenslet optical coupling, cold readout components, and
magnetic shielding. SO will use a microwave SQUID multiplexing (MUX)
readout at an initial multiplexing factor of 1000; the cold (100 mK)
readout components are packaged in a MUX readout module, which is part of
the UFM, and can also be characterized independently. The 100 mK stage TES
bolometer arrays and microwave SQUIDs are sensitive to magnetic fields, and
their measured response will vary with the degree to which they are
magnetically shielded. We present measurements of the magnetic pickup of test
microwave SQUID multiplexers as a study of various shielding configurations for
the Simons Observatory. We discuss how these measurements motivated the
material choice and design of the UFM magnetic shielding.Comment: 5 pages, 6 figures, conference proceedings submitted to IEEE
Transactions on Applied Superconductivit
Measurements of tropospheric ice clouds with a ground-based CMB polarization experiment, POLARBEAR
The polarization of the atmosphere has been a long-standing concern for ground-based experiments targeting cosmic microwave background (CMB) polarization. Ice crystals in upper tropospheric clouds scatter thermal radiation from the ground and produce a horizontally polarized signal. We report a detailed analysis of the cloud signal using a ground-based CMB experiment, Polarbear, located at the Atacama desert in Chile and observing at 150 GHz. We observe horizontally polarized temporal increases of low-frequency fluctuations ("polarized bursts," hereafter) of 720.1 K when clouds appear in a webcam monitoring the telescope and the sky. The hypothesis of no correlation between polarized bursts and clouds is rejected with >24\u3c3 statistical significance using three years of data. We consider many other possibilities including instrumental and environmental effects, and find no reasons other than clouds that can explain the data better. We also discuss the impact of the cloud polarization on future ground-based CMB polarization experiments
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