68 research outputs found
Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder
A pathfinder version of CHIME (the Canadian Hydrogen Intensity Mapping
Experiment) is currently being commissioned at the Dominion Radio Astrophysical
Observatory (DRAO) in Penticton, BC. The instrument is a hybrid cylindrical
interferometer designed to measure the large scale neutral hydrogen power
spectrum across the redshift range 0.8 to 2.5. The power spectrum will be used
to measure the baryon acoustic oscillation (BAO) scale across this poorly
probed redshift range where dark energy becomes a significant contributor to
the evolution of the Universe. The instrument revives the cylinder design in
radio astronomy with a wide field survey as a primary goal. Modern low-noise
amplifiers and digital processing remove the necessity for the analog
beamforming that characterized previous designs. The Pathfinder consists of two
cylinders 37\,m long by 20\,m wide oriented north-south for a total collecting
area of 1,500 square meters. The cylinders are stationary with no moving parts,
and form a transit instrument with an instantaneous field of view of
100\,degrees by 1-2\,degrees. Each CHIME Pathfinder cylinder has a
feedline with 64 dual polarization feeds placed every 30\,cm which
Nyquist sample the north-south sky over much of the frequency band. The signals
from each dual-polarization feed are independently amplified, filtered to
400-800\,MHz, and directly sampled at 800\,MSps using 8 bits. The correlator is
an FX design, where the Fourier transform channelization is performed in FPGAs,
which are interfaced to a set of GPUs that compute the correlation matrix. The
CHIME Pathfinder is a 1/10th scale prototype version of CHIME and is designed
to detect the BAO feature and constrain the distance-redshift relation.Comment: 20 pages, 12 figures. submitted to Proc. SPIE, Astronomical
Telescopes + Instrumentation (2014
The Lyot project: toward exoplanet imaging and spectroscopy
Among the adaptive optics systems available to astronomers, the US Air Force Advanced Electro-Optical System (AEOS) is unique because it delivers very high order wave front correction. The Lyot Project includes the construction and installation of the world’s first diffraction-limited, optimized coronagraph that exploits the full astronomical potential of AEOS and represents a critical step toward the long-term goal of directly imaging and studying extrasolar planets (a.k.a. “exoplanets”). We provide an update on the Project, whose coronagraph saw first light in March 2004. The coronagraph is operating at least as well as predicted by simulations, and a survey of nearby stars has begun
Calibrating CHIME, A New Radio Interferometer to Probe Dark Energy
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit
interferometer currently being built at the Dominion Radio Astrophysical
Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral
hydrogen in the frequency range 400 -- 800\,MHz over half of the sky, producing
a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 --
2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that
will yield constraints on the BAO power spectrum and provide a test-bed for our
calibration scheme. I will discuss the CHIME calibration requirements and
describe instrumentation we are developing to meet these requirements
Cosmological Parameters from Pre-Planck CMB Measurements
Recent data from the WMAP, ACT and SPT experiments provide precise
measurements of the cosmic microwave background temperature power spectrum over
a wide range of angular scales. The combination of these observations is well
fit by the standard, spatially flat LCDM cosmological model, constraining six
free parameters to within a few percent. The scalar spectral index, n_s =
0.9690 +/- 0.0089, is less than unity at the 3.6 sigma level, consistent with
simple models of inflation. The damping tail of the power spectrum at high
resolution, combined with the amplitude of gravitational lensing measured by
ACT and SPT, constrains the effective number of relativistic species to be
N_eff = 3.28 +/- 0.40, in agreement with the standard model's three species of
light neutrinos.Comment: 5 pages, 4 figure
Limits on the ultra-bright Fast Radio Burst population from the CHIME Pathfinder
We present results from a new incoherent-beam Fast Radio Burst (FRB) search
on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its
large instantaneous field of view (FoV) and relative thermal insensitivity
allow us to probe the ultra-bright tail of the FRB distribution, and to test a
recent claim that this distribution's slope, , is quite small. A 256-input incoherent beamformer was
deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were
described by a single power-law with , we would expect an FRB
detection every few days, making this the fastest survey on sky at present. We
collected 1268 hours of data, amounting to one of the largest exposures of any
FRB survey, with over 2.4\,\,10\,deg\,hrs. Having seen no
bursts, we have constrained the rate of extremely bright events to
\,sky\,day above \,220 Jy\,ms
for between 1.3 and 100\,ms, at 400--800\,MHz. The non-detection also
allows us to rule out with 95 confidence, after
marginalizing over uncertainties in the GBT rate at 700--900\,MHz, though we
show that for a cosmological population and a large dynamic range in flux
density, is brightness-dependent. Since FRBs now extend to large
enough distances that non-Euclidean effects are significant, there is still
expected to be a dearth of faint events and relative excess of bright events.
Nevertheless we have constrained the allowed number of ultra-intense FRBs.
While this does not have significant implications for deeper, large-FoV surveys
like full CHIME and APERTIF, it does have important consequences for other
wide-field, small dish experiments
Cosmological parameters from pre-Planck CMB measurements: a 2017 update
We present cosmological constraints from the combination of the full mission nine-year WMAP release and small-scale temperature data from the pre-Planck Atacama Cosmology Telescope (ACT) and South Pole Telescope (SPT) generation of instruments. This is an update of the analysis presented in Calabrese et al. [Phys. Rev. D 87, 103012 (2013)], and highlights the impact on ΛCDM cosmology of a 0.06 eV massive neutrino—which was assumed in the Planck analysis but not in the ACT/SPT analyses—and a Planck-cleaned measurement of the optical depth to reionization. We show that cosmological constraints are now strong enough that small differences in assumptions about reionization and neutrino mass give systematic differences which are clearly detectable in the data. We recommend that these updated results be used when comparing cosmological constraints from WMAP, ACT and SPT with other surveys or with current and future full-mission Planck cosmology. Cosmological parameter chains are publicly available on the NASA’s LAMBDA data archive
Design and implementation of a noise temperature measurement system for the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX)
This paper describes the design, implementation, and verification of a
test-bed for determining the noise temperature of radio antennas operating
between 400-800MHz. The requirements for this test-bed were driven by the HIRAX
experiment, which uses antennas with embedded amplification, making system
noise characterization difficult in the laboratory. The test-bed consists of
two large cylindrical cavities, each containing radio-frequency (RF) absorber
held at different temperatures (300K and 77K), allowing a measurement of system
noise temperature through the well-known 'Y-factor' method. The apparatus has
been constructed at Yale, and over the course of the past year has undergone
detailed verification measurements. To date, three preliminary noise
temperature measurement sets have been conducted using the system, putting us
on track to make the first noise temperature measurements of the HIRAX feed and
perform the first analysis of feed repeatability.Comment: 19 pages, 12 figure
Packed Ultra-wideband Mapping Array (PUMA): A Radio Telescope for Cosmology and Transients
PUMA is a proposal for an ultra-wideband, low-resolution and transit
interferometric radio telescope operating at . Its
design is driven by six science goals which span three science themes: the
physics of dark energy (measuring the expansion history and growth of the
universe up to ), the physics of inflation (constraining primordial
non-Gaussianity and primordial features) and the transient radio sky (detecting
one million fast radio bursts and following up SKA-discovered pulsars). We
propose two array configurations composed of hexagonally close-packed 6m dish
arrangements with 50% fill factor. The initial 5,000 element 'petite array' is
scientifically compelling, and can act as a demonstrator and a stepping stone
to the full 32,000 element 'full array'. Viewed as a 21cm intensity mapping
telescope, the program has the noise equivalent of a traditional spectroscopic
galaxy survey comprised of 0.6 and 2.5 billion galaxies at a comoving
wavenumber of spanning the redshift range for the petite and full configurations, respectively. At redshifts beyond
, the 21cm technique is a uniquely powerful way of mapping the universe,
while the low-redshift range will allow for numerous cross-correlations with
existing and upcoming surveys. This program is enabled by the development of
ultra-wideband radio feeds, cost-effective dish construction methods, commodity
radio-frequency electronics driven by the telecommunication industry and the
emergence of sufficient computing power to facilitate real-time signal
processing that exploits the full potential of massive radio arrays. The
project has an estimated construction cost of 55 and 330 million FY19 USD for
the petite and full array configurations. Including R&D, design, operations and
science analysis, the cost rises to 125 and 600 million FY19 USD, respectively.Comment: 10 pages + references, 3 figures, 3 tables; project white paper
submitted to the Astro2020 decadal survey; further details in updated
arXiv:1810.0957
Packed Ultra-wideband Mapping Array (PUMA): Astro2020 RFI Response
The Packed Ultra-wideband Mapping Array (PUMA) is a proposed low-resolution
transit interferometric radio telescope operating over the frequency range 200
- 1100MHz. Its rich science portfolio will include measuring structure in the
universe from redshift z = 0.3 to 6 using 21cm intensity mapping, detecting one
million fast radio bursts, and monitoring thousands of pulsars. It will allow
PUMA to advance science in three different areas of physics (the physics of
dark energy, the physics of cosmic inflation and time-domain astrophysics).
This document is a response to a request for information (RFI) by the Panel on
Radio, Millimeter, and Submillimeter Observations from the Ground (RMS) of the
Decadal Survey on Astronomy and Astrophysics 2020. We present the science case
of PUMA, the development path and major risks to the project.Comment: 46 pages, 16 figures, 7 tables; response to the request for
information (RFI) by the Panel on Radio, Millimeter, and Submillimeter
Observations from the Ground (RMS) of the Astro2020 Decadal Survey regarding
PUMA APC submission (arXiv:1907.12559); v2: updated with correct bbl fil
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