7 research outputs found
Detection of Crab Giant Pulses Using the Mileura Widefield Array Low Frequency Demonstrator Field Prototype System
We report on the detection of giant pulses from the Crab Nebula pulsar at a
frequency of 200 MHz using the field deployment system designed for the Mileura
Widefield Array's Low Frequency Demonstrator (MWA-LFD). Our observations are
among the first high-quality detections at such low frequencies. The measured
pulse shapes are deconvolved for interstellar pulse broadening, yielding a
pulse-broadening time of 670100 s, and the implied strength of
scattering (scattering measure) is the lowest that is estimated towards the
Crab nebula from observations made so far. The sensitivity of the system is
largely dictated by the sky background, and our simple equipment is capable of
detecting pulses that are brighter than 9 kJy in amplitude. The brightest
giant pulse detected in our data has a peak amplitude of 50 kJy, and the
implied brightness temperature is K. We discuss the giant pulse
detection prospects with the full MWA-LFD system. With a sensitivity over two
orders of magnitude larger than the prototype equipment, the full system will
be capable of detecting such bright giant pulses out to a wide range of
Galactic distances; from 8 to 30 kpc depending on the frequency.
The MWA-LFD will thus be a highly promising instrument for the studies of giant
pulses and other fast radio transients at low frequencies.Comment: 10 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
First geodetic observations using new VLBI stations ASKAP-29 and WARK12M
We report the results of a successful 7 hour 1.4 GHz VLBI experiment using
two new stations, ASKAP-29 located in Western Australia and WARK12M located on
the North Island of New Zealand. This was the first geodetic VLBI observing
session with the participation of these new stations. We have determined the
positions of ASKAP-29 and WARK12M. Random errors on position estimates are
150-200 mm for the vertical component and 40-50 mm for the horizontal
component. Systematic errors caused by the unmodeled ionosphere path delay may
reach 1.3 m for the vertical component.Comment: 11 pages, 6 flgures, 4 table
Calibration database for the Murchison Widefield Array All-Sky Virtual Observatory
We present a calibration component for the Murchison Widefield Array All-Sky
Virtual Observatory (MWA ASVO) utilising a newly developed PostgreSQL database
of calibration solutions. Since its inauguration in 2013, the MWA has recorded
over thirty-four petabytes of data archived at the Pawsey Supercomputing
Centre. According to the MWA Data Access policy, data become publicly available
eighteen months after collection. Therefore, most of the archival data are now
available to the public. Access to public data was provided in 2017 via the MWA
ASVO interface, which allowed researchers worldwide to download MWA
uncalibrated data in standard radio astronomy data formats (CASA measurement
sets or UV FITS files). The addition of the MWA ASVO calibration feature opens
a new, powerful avenue for researchers without a detailed knowledge of the MWA
telescope and data processing to download calibrated visibility data and create
images using standard radio-astronomy software packages. In order to populate
the database with calibration solutions from the last six years we developed
fully automated pipelines. A near-real-time pipeline has been used to process
new calibration observations as soon as they are collected and upload
calibration solutions to the database, which enables monitoring of the
interferometric performance of the telescope. Based on this database we present
an analysis of the stability of the MWA calibration solutions over long time
intervals.Comment: 12 pages, 9 figures, Accepted for publication in PAS
Detection of Crab Giant Pulses Using the Mileura Widefield Array Low Frequency Demonstrator Field Prototype System
We report on the detection of giant pulses from the Crab Nebula pulsar at a frequency of 200 MHz using the field deployment system designed for the Mileura Widefield Array's Low Frequency Demonstrator (MWA-LFD). Our observations are among the first high-quality detections at such low frequencies. The measured pulse shapes are deconvolved for interstellar pulse broadening, yielding a pulse-broadening time of 670 ± 100 μs, and the implied strength of scattering (scattering measure) is the lowest that is estimated toward the Crab Nebula from observations made so far. The sensitivity of the system is largely dictated by the sky background, and our simple equipment is capable of detecting pulses that are brighter than ∼9 kJy in amplitude. The brightest giant pulse detected in our data has a peak amplitude of ∼50 kJy, and the implied brightness temperature is 10 31.6 K. We discuss the giant pulse detection prospects with the full MWA-LFD system. With a sensitivity over 2 orders of magnitude larger than the prototype equipment, the full system will be capable of detecting such bright giant pulses out to a wide range of Galactic distances; from ∼ 15 to ∼30 kpc depending on the frequency. The MWA-LFD will thus be a highly promising instrument for the studies of giant pulses and other fast radio transients at low frequencies
VAST: An ASKAP Survey for Variables and Slow Transients
The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an
unprecedented opportunity to investigate the transient sky at radio
wavelengths. In this paper we present VAST, an ASKAP survey for Variables and
Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP
to enable the discovery and investigation of variable and transient phenomena
from the local to the cosmological, including flare stars, intermittent
pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar
scintillation, radio supernovae and orphan afterglows of gamma ray bursts. In
addition, it will allow us to probe unexplored regions of parameter space where
new classes of transient sources may be detected. In this paper we review the
known radio transient and variable populations and the current results from
blind radio surveys. We outline a comprehensive program based on a multi-tiered
survey strategy to characterise the radio transient sky through detection and
monitoring of transient and variable sources on the ASKAP imaging timescales of
five seconds and greater. We also present an analysis of the expected source
populations that we will be able to detect with VAST.Comment: 29 pages, 8 figures. Submitted for publication in Pub. Astron. Soc.
Australi
Field Deployment of Prototype Antenna Tiles for the Mileura Widefield Array--Low Frequency Demonstrator
Experiments were performed with prototype antenna tiles for the Mileura
Widefield Array--Low Frequency Demonstrator (MWA-LFD) to better understand the
widefield, wideband properties of their design and to characterize the radio
frequency interference (RFI) between 80 and 300 MHz at the site in Western
Australia. Observations acquired during the six month deployment confirmed the
predicted sensitivity of the antennas, sky-noise dominated system temperatures,
and phase-coherent interferometric measurements. The radio spectrum is
remarkably free of strong terrestrial signals, with the exception of two narrow
frequency bands allocated to satellite downlinks and rare bursts due to
ground-based transmissions being scattered from aircraft and meteor trails.
Results indicate the potential of the MWA-LFD to make significant achievements
in its three key science objectives: epoch of reionziation science,
heliospheric science, and radio transient detection.Comment: Accepted by AJ. 17 pages with figure