ASKAP Commissioning and Early Science
The ASKAP Survey Science WALLABY (Widefield ASKAP L-band Legacy All-sky Blind surveY) Team has created a preliminary ASKAP 21-cm radio continuum map of the region around the southern pinwheel galaxy M83 (see box in bottom right). It shows radio emissions from M83, as well as more unfamiliar structures likely to be associated with extremely distant supermassive black holes.
The structural detail distinguishable in the map clearly demonstrates the capability and science potential of ASKAP. The wide field of view and the fast sky-survey capabilities are enabling the WALLABY Early Science Team to study gas in nearby galaxy groups in unprecedented detail and to observe whole groups at once. The full WALLABY survey (36 antennas) will extend this to the entire southern sky.
Observations were taken during the day on 31 December 2016 and this specific field was chosen to minimise solar interference. The central map is the fully mosaicked 30 square degree field of view, that was simultaneously observed with 36 beams. The outer boxes highlight some of the key features detectable after approximately 10 hours of observations, with 10 ASKAP antennas, 192 MHz bandwidth and a 42″ x 17″ synthesised beam.
According to NED (NASA/IPAC Extragalactic Database) the field contains ~1900 catalogued NVSS sources to a peak flux of ~2.5 mJy/beam, ~140 of which have redshifts. The approximate rms noise in our current image is 0.1 mJy. This field contains 28 HIPASS sources.
The maps were made using the ASKAP Science Data Processor software, ASKAPsoft, which is an automated pipeline running on the Pawsey Supercomputing system. These observations have been made possible through ongoing efforts from engineers, software designers, and scientists in CASS, ACES (ASKAP Commissioning & Early Science team), and the WALLABY Survey Science team.
- 10.1 hrs daytime observing
- 192 MHz bandwidth around central frequency 1344.5 MHz
- 10 antennas
- 36 beams
- ASKAPsoft pipeline version 0.16.1 (with non‐default parameters)
- Observational data taken on 31 December 2016.
30th Phased Array Feed (PAF) Receiver Installed
The 30th phased array feed receiver (PAF) was fitted to AK33, on 8 December 2016. As we continue to develop our PAF technology, the commissioning results are already showing how valuable it is for radio astronomy. We’re steaming ahead with the installation of the Mk II PAF receivers on ASKAP, and it’s exciting that this Australian technology will be used on other telescopes around the world.
January Commissioning Run
With an increasing number of active antennas in the ASKAP array, the commissioning team has been experimenting with new ways to test the capabilities of the expandingsystem. With a total of 36 antennas and a wide field of view, ASKAPwas designed to have very good instantaneous UV coverage. This will alloweffective characterisation of time-variable emissions and improve the dynamic range of the telescope.
As proof that we are beginning to see a glimpse of the system’s full capability, the commissioning team decided to try making snapshot images of the reference source used for beamforming – the Sun itself. The disk of the Sun fits neatly inside the primary beam of ASKAP’s 12m antennas, so it is possible to image the whole surface in one snapshot.
With 16 active antennas operating during our January commissioning session, we observed the sun for 15 minutes each day over 5 days, producing radio contour images such as the one shown below (in yellow) over 48 MHz of bandwidth at a centre frequency of 936 MHz. We also made an animation of it here.
The structures detected in these images match features seen at other wavelengths at the same time (for example, the NASA Solar Dynamics Observatory ultra-violet image shown in blue). This is an encouraging demonstration of the system as a whole and highlights some of the interesting sciencecapabilities that the telescope has, in addition to itsplanned large-scale survey capabilities.
|The Sun in radio with a prominent solar flare (quick reduction only).
||Our image is very similar to this Fe IX image from SolarMonitor.org made on the same day.|