ASKAP Early Science is underway and by the end of 2016, 30 antennas will be fitted with the second generation of CSIRO’s multi-award winning phased array feed (PAF) receiver.
ASKAP Early Science kicks off
ASKAP’s Early Science programme formally began on 7 October 2016, using twelve of the antennas equipped with second generation (Mk II) phased array feed (PAF) receivers.
Close to two hundred hours of observations have already been executed in support of the Early Science programme for the WALLABY survey, in order to study the wide-field, low-column density neutral hydrogen properties of local galaxy groups.
The central panel of the image above shows a full 36-beam, dual-position (2 x 10 h) interleaved continuum image of the field surrounding NGC 7232. On the left are HI intensity and velocity field images of the nearby spiral galaxy IC 5201. The panels on the right provide a closer look at the continuum image, including some well-resolved structures with complex morphologies. The map contains about 2,500 unique radio components.
Development of the ASKAP telescope beyond the Early Science array continues apace. Current commissioning activities are focusing on improvements to the calibration and imaging pipelines, polarisation, and use of the on-dish calibration system. The year 2016 will end with 30 Mk II PAFs installed on the array, though not all of them will be operational at that time.
World’s first VLBI with PAFs
In a world first, CSIRO has shown that VLBI can be done with two PAFs.
For their experiment on 27 October 2016, the VLBI test team observed with a PAF-equipped ASKAP antenna in Western Australia and with the Effelsberg PAF on the 64-metre Parkes Radio Telescope on the other side of the country.
A previous link-up with an ASKAP antenna had shown it was feasible to use a single PAF for this high resolution observing technique, but dual-PAF observations are more complex. New firmware had to be installed on the ASKAP antenna to allow access to the raw data, and the data streaming from both PAFs had to be resampled and converted to VLBI format.
Three hours’ worth of data was recorded and is now being analysed.
The goal was to observe the galaxy PKS B1740–517. CSIRO astronomers had discovered neutral hydrogen (HI) gas in this galaxy when using ASKAP’s test array (six antennas fitted with first generation PAFs). They hoped to use VLBI to pinpoint where the gas lies in the galaxy. They used the dual-PAF set-up because they needed to observe at 986 MHz, a frequency covered by the PAFs but not by the conventional feeds available at Parkes or other Australian telescopes used for VLBI.
As well as confirming that the signals from two PAFs can be combined for VLBI, the tests showed how easily ASKAP can ‘multitask’. While one ASKAP antenna was being used for VLBI, another ten were working together to study the same galaxy in a different way.