BETA Data Release Notes

Version 1.0 of the CSIRO ASKAP Science Data Archive (CASDA) was released on 5 November 2015.

The first ASKAP data products have been produced from science commissioning observations taken with the Boolardy Engineering Test Array (BETA). BETA uses six ASKAP antennas equipped with Mark I phased array feeds (PAFs). The ASKAP Commissioning and Early Science (ACES) team are using BETA to carry out a small number of science programs. These have been selected to to explore the astronomy potential and unique wide-field fast survey capabilities of ASKAP and to provide some demonstration data sets to the astronomy community.

The notes below provide further information on the data products released for four separate BETA science programs. These are now available through CASDA.

Getting started with CASDA

To access data products and get started with using CASDA, see the instructions in the CASDA Users Guide.

All BETA observations were taken using a generic project code of 'AS031' and project title 'BETA Science Observations'. Here we advise that for the BETA commissioning data products it is helpful to note the scheduling block numbers as well as the project code. In some cases data from several observing sessions were combined to produce the final data products. In this case the first scheduling block number is used as the identifier for CASDA searches.

Redshifted HI absorption in the quasar PKS2252-089

This project searched for 21-cm absorption, spanning redshifts z = 0.4 - 1.0, of background radio emission in a single 9-beam BETA pointing centred on the quasar PKS2252-089. The data cube shows HI absorption against PKS2252-089 at 883.6MHz (z = 0.6076). HI absorption in the quasar host galaxy was first detected by Curran et al. (2011) using the Green Bank Telescope.

Absorption of background radio emission by neutral hydrogen enables us to measure the line-of-sight kinematics of HI gas in the distant Universe. The excellent radio frequency environment of ASKAP and wide fractional bandwidth means that we can detect HI absorption out to redshifts of 1. Importantly HI can be used to trace neutral gas around radio AGN and their interaction, providing insights into the models used to explain triggering and feedback.

For further information see Allison et al., 2015
Tracing the neutral gas environments of young radio AGN with ASKAP

For details of a recent discovery of HI absorption using ASKAP BETA see Allison et al., 2015, MNRAS, 453, 1249
Discovery of HI gas in a young radio galaxy at z = 0.44 using the Australian Square Kilometre Array Pathfinder

Data Product Details

Scheduling Block(s) 72

Data Notes: Single data cube covering one PAF beam centred on the quasar PKS2252-089, with 16,416 frequency channels spanning a frequency range from 711.5 to 1015.5 MHz.

Pilot observations of radio transients around an intermittent pulsar PSR J1107-5907

This project used BETA observations to search for transient radio sources in the field around the intermittent pulsar PSR J1107-5907. The pulsar is thought to switch between an “off” state in which no emission is detectable, a weak state and a strong state. Several detection algorithms were applied to two-minute snapshot images produced from a 13 hour BETA observation to 1) study the emission from the pulsar, 2) search for other transient emission from elsewhere in the image and 3) compare the results from the different transient detection pipelines. The pulsar was easily detected as a transient source and, over the course of the observations, switched into the strong state three times giving a typical timescale between the strong emission states of 3.7 hours.

This pilot study showed that future transient surveys with ASKAP will have the potential to probe the intermittent pulsar population.

A paper on this work has been accepted by MNRAS. See the astro-ph preprint:
A pilot ASKAP survey of radio transient events in the region around the intermittent pulsar PSR J1107-5907

Data Product Details

Scheduling Block(s) 220

Data Notes: The BETA observations for this project were taken during a single scheduling block of 13 hours. The data products include a single measurement set with the calibrated continuum visibilities together with a set of 391 single-plane snapshot images produced for two-minute intervals.

ASKAP HI Imaging of the Galaxy Group IC 1459

The goal of these observations was to obtain resolved images of neutral hydrogen gas in the galaxy group IC 1459. Neutral hydrogen provides crucial clues about the properties of the inter-stellar medium of galaxies, about galaxies' internal dynamics, and about the interaction between galaxies and the environment around them. Neutral hydrogen is observable in emission through a spectral line at a frequency of ~1.42 GHz. The main ASKAP capability tested by these observations is spectral line imaging of resolved sources.

For further information see Serra et al., 2015, MNRAS, 452, 2680
ASKAP H I imaging of the galaxy group IC 1459

Data Product Details

Scheduling Block(s) 492, 523, 597

Data Notes: The main data product is a spectral line image cube produced from observations taken during three scheduling blocks with a total observing time of 30 hours. The cube has a field of view of six degrees² and 300 spectral channels across a bandwidth of 18.5 MHz, from 1.4025 to 1.4210 GHz, corresponding to a velocity resolution of 8 km/s. The spatial resolution is 70 x 55 arcsec². In addition to the cube, a moment-zero (M0) image and a moment-one (M1) image generated from the cube are also available.

Radio Continuum Observations of the Tucana Region

This project produced arcminute resolution continuum imaging using BETA at 711-1015 MHz, demonstrating the viability and potential of the PAF operating in a wide field and broadband continuum imaging mode. Two sets of observations were taken:

The first set was used to produce an image covering fifty square degrees of the sky in the constellation Tucana. This was made up of five 10-hour observations, each of which cycled between one of two pairs of interleaved fields. Each observation used all nine beams available with BETA.

This image was used to test the Selavy source detection software (Whiting & Humphreys 2012, http://adsabs.harvard.edu/abs/2012PASA...29..371W ) with ASKAP data. This detection algorithm searches an image for 'components' and 'islands' where:

An island is defined by a set of contiguous pixels in a continuum image that have flux densities above a threshold value. This is the primary result of the source-detection. Within this defined region an island may contain one or more components.

A component describes a single compact object, which has been parameterised by a two-dimensional Gaussian fit. The component catalogue is the principle data product used to catalogue the sky.

For this Tucana image 2,134 components and 2,045 islands were detected. Parameters for these are written in two catalogues. (Note: We recommend using the Virtual Observatory services to look at catalogues. See the CASDA User Guide for instructions.)

For the second set, nine beams were deployed and the array cycled through 12 interleaved pointing directions over the course of twelve hours, resulting in a 150 square degree image covering approximately two thirds of the Spitzer South Pole Telescope Deep Field. Three of these twelve hour epochs were observed over the course of a week in order to verify the stability and performance of the PAF, as well as conduct a variability study. One significantly variable source was found by comparing the observations to those of SUMSS. The deep mosaic formed from the combined epochs has an effective noise level of about 1 mJy/beam (with a thermal noise limit of 0.375 mJy/beam) and contains 3,722 radio sources above five times the effective noise level. The 33% fractional bandwidth of BETA allows robust estimates of the spectral index of 1,037 of these sources.

A publication on this work has been submitted.

Data Product Details

Scheduling Block(s) Set 1: 609, 617, 639, 643, 660
Set 2: 1206, 1229, 1231

Data Notes: Two different sets of BETA data products are provided for the Tucana region:
The data products included with scheduling Block 609 were combined from five scheduling blocks, taken over 50 hours of observing, to produce a single image of the Tucana region covering 50 square degrees on the sky.
A second set of 21 image data products for the Tucana region were produced from BETA observations taken in December 2014. The mosaic observations covered 12 separate pointing on the sky with nine beams for each pointing. Observations were taken during three sessions corresponding to scheduling blocks 1206, 1209 and 1231 with a total observing time of 33 hours.
For each of the three scheduling blocks - five images correspond to one image for each of the four sub-bands plus an additional image averaged over the sub-bands. For SB 1206, a further six images are also provided. These correspond to averages over the three epochs for each sub-band (four images), a single image averaged over all visibility data, and a single spectral image map.

Scheduling Block(s)	72
Data Notes:	Single data cube covering one PAF beam centred on the quasar PKS2252-089, with 16,416 frequency channels spanning a frequency range from 711.5 to 1015.5 MHz.

Scheduling Block(s)	220
Data Notes:	The BETA observations for this project were taken during a single scheduling block of 13 hours. The data products include a single measurement set with the calibrated continuum visibilities together with a set of 391 single-plane snapshot images produced for two-minute intervals.