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ASKAP Technical Update
CSIRO Astronomy and Space Science December 2011

The ASKAP Technical Update contains a brief summary of recent science and technical developments and milestones related to the Australian SKA Pathfinder (ASKAP) project. Each issue also looks at an aspect of key ASKAP activity. Previous issues can be read online at www.atnf.csiro.au/projects/askap.

PAF's first `look' at Virgo A
CSIRO is pleased to release an image from the Par kes Testbed Facility (PTF) which shows, for the fir st time, the raw on-sky por t patterns from an ASKAP Phased Array Feed (PAF) installed at prime focus of the 12-m testbed antenna. The image is a striking demonstration of recent PAF testing at the ASKAP testbed antenna installed at CSIRO's Par kes Obser vator y. It matches the expected performance of the system, fur ther validating chequerboard PAFs as rapid imaging devices for radio astronomy. Following installation of the fir st fullsized prototype PAF on the Patriot

12-m antenna in July (see September's ASKAP Technical Update), tests were r un during the September­November period, correlating each of the 188 por ts on the testbed antenna with the central horn of the 20-cm multibeam receiver on CSIRO's Par kes 64-m radio telescope (`The Dish'). The Dish tracked the powerful radio galaxy Virgo A while the PTF executed a raster scan about the radio source to map out a 14 square degree patch of each PAF por t pattern. The two polarisations of the central beam of the 20cm multibeam receiver were connected to por ts 189 and 190 of the beamformer, using an RF over fibre (RFoF) link.

Each of the 94 individual squares represent a por t on the PAF, while another 94 por ts with the or thogonal polarization (not shown), make up the total 188 por ts. The central por ts, close to the antenna bore-sight, show the source well-centred, while at the edges the source is radially offset, and shows larger and asymmetric side-lobes, just as expected. The Par kes 64-m dish was an essential instr ument for these measurements, providing a stable and powerful reference signal that accelerates the data collecting and calibration enormously. This result and other s in the pipeline have given the ASKAP team great confidence that the PAF and downstream signal processing electronics is reliable and robust, not just over hour s but over days and weeks. It is a culmination of over three year s of cutting edge research and development by CSIRO staff and is a significant milestone towards demonstrating PAF technology for radio astronomy. Ant Schinckel, CSIRO ASKAP Project Director, was quick to praise the ASKAP team for the excellence of their wor k. "This represents a group effor t ­ the entire ASKAP team, from the PAF designer s and builder s, through the data transpor t group to the digital backend team and software group. This is a great result for the team!" he said.

BETA installation in full swing
> The coloured image within each square represents the power received at each PAF port. The colour scale in each image represents logarithmic intensity over approximately 55 dB in range and comprises 40 x 1 MHz summed channels, spanning frequency range 1.2­1.5 GHz. Each image is normalised to its peak value. Credit: Aidan Hotan, CSIRO. The installation of the fir st three PAF receiver s on ASKAP antennas at the MRO was a major milestone recently achieved by the ASKAP team.


These are the second, third and four th complete PAFs built to the ASKAP design (the prototype PAF is installed on the testbed antenna at Par kes), but the fir st to be deployed to the ASKAP site. The ASKAP team is wor king to have all three receiver s and associated electronics functioning at the MRO by the year's end. This instr ument will represent the fir st half of engineering and scientific commissioning instr ument, the Boolardy Engineering Test Array (BETA). BETA will provide an invaluable testbed instr ument for the ASKAP team to learn how to `drive' the PAF receiver s and achieve the best possible performance . While the central ASKAP Control Building is assembled and fitted-out on site, the correlator and beam-former electronics for the fir st half of BETA have been temporarily accommodated at the MRO in a modified shipping container, known as the `BETA Box'. The fibre link between the MRO and Per th (used in July 2011 for a live `e-VLBI demonstration) is currently awaiting final sign-off before becoming fully operational and achieving full bandwidth.

Boolardy Engineering Test Array (BETA)
BETA will comprise six ASKAP antennas at the MRO with PAFs and a correlator complete with full 300 MHz ASKAP bandwidth and 36 formed beams covering six 30 square degree fields. While primarily an engineering testbed, BETA will also be an entr y point for the ten ASKAP Sur vey Science Teams to become actively involved in preliminar y scientific obser vations, analysing data in preparation for deliver y of the full 36 antenna array. Although BETA is not a science instr ument, it is more than likely some real `ear ly science' will be under taken, to assist the SCOM team with the full fit-out of the ASKAP radio telescope.

commissioning plans, par ticular ly on BETA and the MRO. Guided by the ver y positive outcomes on the 12-m testbed at Par kes, main objectives of commissioning at the MRO in the coming months are single dish PAF and beamformer testing and phase closure demonstration.

Phase Closure Demonstration
Once reliable beam-weights have been obtained and the basic single-dish mode of operation has been validated, the next objective is to obtain correlation fir st on a single baseline (between two PAF antennas) and then on three baselines (three PAF antennas). The latter should yield `phase closure'. In the fir st instance signal correlation will use a relatively low bandwidth (16 MHz) capturing baseband data for a single formed-beam on a pointsource calibrator and correlating in software. Once validated, additional beams will be added and more complex fields obser ved. These measurements will move to multiple beam imaging of simple astronomical fields during ear ly 2012, paving the way for more complex imaging obser vations as we acquire additional antennas and the fullbandwidth, real-time correlator.
For further information: Flor nes Conway- Der ley C S I R O A s t r o n o my a n d S p a c e S c i e n c e Email: flor nes .conway- der ley @ csir o. au Web: w w w. atnf.csiro. au/projec t s /a sk ap

Single Dish Testing
Using at Par scans MRO Virgo software and firmware validated kes, the team will under take with ASKAP antennas at the on bright calibrator s such as A in single-dish mode.

BETA commissioning gears up
The ASKAP System Commissioning Team (SCOM) has been busy over the last several months wor king with the fir st PAF receiver at Par kes and producing images such as the montage on the front page. SCOM forms par t of the wider System Engineering, Integration and Commissioning (SEIC) team and takes specific responsibility for executing

In the low-RFI environment at the MRO the team expects to achieve enough sensitivity to determine fir st-order beamweights, investigate a range of PAF and beamforming questions and continue to confirm basic functionality of the system. Several high-performance and wellcharacterised feedhorn (single pixel) receiver s are also available to provide reference signals using exactly the same proven techniques demonstrated at Par kes.

>ASKAP antennas installed with PAFs at the MRO. When fitted with associated electronics, they will represent the first half of BETA. Credit: Barry Turner, CSIRO.