9 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 extraordinary linear polarisation structure of the southern Centaurus A lobe revealed by ASKAP
We present observations of linear polarisation in the southern radio lobe of
Centaurus A, conducted during commissioning of the Australian Square Kilometre
Array Pathfinder (ASKAP) telescope. We used 16 antennas to observe a 30 square
degree region in a single 12 hour pointing over a 240 MHz band centred on 913
MHz. Our observations achieve an angular resolution of arcseconds
(480 parsecs), a maximum recoverable angular scale of 30 arcminutes, and a
full-band sensitivity of 85 \muupJy beam. The resulting maps of
polarisation and Faraday rotation are amongst the most detailed ever made for
radio lobes, with of order 10 resolution elements covering the source. We
describe several as-yet unreported observational features of the lobe,
including its detailed peak Faraday depth structure, and intricate networks of
depolarised filaments. These results demonstrate the exciting capabilities of
ASKAP for widefield radio polarimetry.Comment: 10 pages, 6 figures. Accepted in "The Power of Faraday Tomography"
special issue of Galaxie
A catalogue of radio supernova remnants and candidate supernova remnants in the EMU/POSSUM Galactic pilot field
We use data from the pilot observations of the EMU/POSSUM surveysto study the ‘missing supernova remnant (SNR) problem’, the discrepancy between the number of Galactic SNRs that have been observed, and the number that are estimated to exist. The Evolutionary Map of the Universe (EMU) and the Polarization Sky Survey of the Universe’s Magnetism (POSSUM) are radio sky surveys that are conducted using the Australian Square Kilometre Array Pathfinder (ASKAP). We report on the properties of seven known SNRs in the joint Galactic pilot field, with an approximate longitude and latitude of 323◦ ≤ l ≤ 330◦ and −4◦ ≤ b ≤ 2◦, respectively, and identify 21 SNR candidates. Of these, four have been previously identified as SNR candidates, three were previously listed as a single SNR, 13 have not been previously studied, and one has been studied in the infrared. These are the first discoveries of Galactic SNR candidates with EMU/POSSUM and, if confirmed, they will increase the SNR density in this field by a factor of 4. By comparing our SNR candidates to the known Galactic SNR population, we demonstrate that many of these sources were likely missed in previous surveys due to their small angular size and/or low surface brightness. We suspect that there are SNRs in this field that remain undetected due to limitations set by the local background and confusion with other radio sources. The results of this paper demonstrate the potential of the full EMU/POSSUM surveys to uncover more of the missing Galactic SNR population
The economic balance of dealing with the concept of Kočičí vrch-Ležáky stone quarry in relation to variant plans of extraction and deposition
Import 30/07/2007Prezenční542 - Institut hornického inženýrství a bezpečnost