Starting the year with new discoveries and a new guide to how ASKAP works

As ASKAP continues its countdown to full-scale survey operations, exciting discoveries are already emerging from the latest observations. Shortly after the full release of images from the Rapid ASKAP Continuum Survey (RACS) low band data set, L. Ighina and colleagues reported their discovery of the most distant radio-loud quasar, found in RACS by cross-referencing radio sources with high-redshift optical quasar detections. This record-breaking galaxy existed less than one billion years after the big bang, challenging our ideas of how long it takes galaxies to form.

The first RACS band was observed in roughly 300 hours spread over several months. Observations for the second RACS band (with a centre frequency of 1296 MHz) commenced in late December 2020 and are already about 90% complete thanks to Improvements in scheduling efficiency and operational procedures.

Linking astronomers to their instruments

ASKAP’s record-breaking achievements rely on over a decade of technology development, design and construction that is coming to fruition through observatory projects and pilot surveys. Today, we are pleased to announce publication of a new resource for the ASKAP community – a comprehensive technical description of the telescope and its many subsystems.

Published today on the astro-ph preprint archive and accepted for publication in PASA, our system description paper outlines how ASKAP achieves its rapid survey speed. It is also a thorough reference for astronomers wishing to understand more about the origins of the data they are working with.

One of the paradigm-shifts associated with ASKAP is greater separation between the early stages of data processing and the astronomers who use the telescope’s data for their research. ASKAP’s operations team provides calibrated images and catalogues to the community via a science data archive. Many other radio telescopes provide raw data products that must be calibrated and imaged by astronomers themselves. ASKAP’s approach was necessary due to the telescope’s extremely high data rates and it also gives astronomers more time to focus on their chosen research topic. However, being removed from processing activities can also make the calibration and imaging algorithms less transparent, leading to increased risk of misinterpretation.

Rigorous research depends on a deep understanding of the data upon which a result is based. To give astronomers a complete picture of how ASKAP works, we are publishing a series of papers describing the telescope’s technical aspects in detail. The first paper in the series (released today) covers the telescope hardware, control system software and subsystem design. Future papers will expand on the supercomputing platform, image processing software and system performance.

With millions of monitoring points, many thousands of components, and several layers of subsystem hierarchy, ASKAP’s level of complexity was difficult to capture in a single document. We have attempted to focus on aspects of the system that determine its capabilities or have the potential to leave an imprint in the data. Readers will follow the signal path from dish surface through digitisation, channelisation, beamforming, correlation, formatting, imaging and ultimately deposit into CASDA, the science data archive.

We hope that this new publication will provide a useful reference for the science community, and for the teams currently designing and prototyping the Square Kilometre Array.