ATCA Observing

Remote observing with the ATCA is the default mode of observing, but it is also possible to observe from the Marsfield Science Operations Centre (SOC) or the Perth SOC. Observing at the Narrabri site is encouraged for observers who wish to visit the observatory, or for observers wanting to become familiar with BIGCAT, and for complex or non-standard observations, or in other circumstances where this is the more sensible option. 

The Narrabri observatory is considered a remote observing site with regard to support levels for normal observations. New observers can be trained remotely, but are encouraged to travel to the SOC if they prefer. 

Array configurations

At least one 6km configuration, a 1.5 km configuration, a 750 m configuration and all the H168, H214 and H75 hybrid configurations will be offered during the semester. Configurations will only be scheduled if there is sufficient proposal demand for them.

Rapid response observations

We welcome NAPA proposals for rapid response observations (within ~10 minutes of an alert). A rapid response mode for the ATCA is now in operation. Proposers seeking to use this mode must contact Jamie Stevens (Jamie.Stevens [at] csiro.au) and demonstrate a working triggering mechanism before being allowed to send triggers to the telescope. 

BIGCAT correlator modes

BIGCAT is a highly flexible, GPU-based software correlator capable of supporting almost any required spectral resolution. To simplify scheduling and provide clear guidance for observers, the observatory offers a set of primary correlator modes that we believe can cover most science use cases. Custom configurations can also be accommodated—within data-rate limits—and prospective users are encouraged to contact observatory staff well ahead of proposal deadlines to discuss specific requirements.

All ATCA proposals will need to create new observations tables to reflect the new BIGCAT observing modes. If you have an existing observations table that specifies CABB observing modes, you may upload it to the OPAL observations table editor and update it with the new BIGCAT modes.

Primary BIGCAT modes:

– Continuum: 1 MHz channels across 4×1.92 GHz IFs 

– Spectral line 18 khz: 18 kHz channels across 4×1.92 GHz IFs

– Spectral line 9 khz: 9 kHz channels across 1×1.92 GHz IF, 1 MHz channels on remaining IFs

– Zoom mode (4×0.5 kHz): Users can place up to 4 zooms at 0.5 kHz resolution across 2 MHz bw in each 128 MHz subband. Note that data-rate limits will apply. 

– Zoom mode (4×0.06 kHz): Users can place up to 4 zooms at 0.06 kHz resolution across 2 MHz bw in each 128 MHz subband. Note that data-rate limits will apply.

– Tied Array mode: ATCA used as tied array. Primarily used for VLBI experiments

– Pulsar binning: *note this mode is still being implemented

– Other: Please use this option in the ATCA observations table and discuss specific requirements in the proposal. 

ATCA receivers and frequency ranges

The 16-cm band receivers provide an instantaneous frequency coverage from 1.1 to 3.1 GHz (although the usable bandwidth is reduced by typically 30% by Radio Frequency Interference [RFI] — the impact of RFI on the 16cm band can be seen at this webpage.). The 16-cm band receivers have an improved sensitivity over the original 20- and 13-cm receivers, and include new ortho-mode-transducers, significantly improving the polarisation performance toward the top end of the band. 

The 4-cm band receivers cover the band from 4 GHz to 12 GHz. These receivers provide significantly improved system temperatures over the original 6- and 3-cm receivers. The focus positions for the antennas in the 4cm band differ from those of other bands, which should be borne in mind if changing between bands during an observation. It takes about 2 minutes to refocus the antennas. 

In the 15-mm (16–25 GHz), 7-mm (30–50 GHz) and 3-mm (83.5–106 GHz) bands, two 2GHz-wide intermediate frequency bands may be selected within an 8 GHz bandwidth. In the 7-mm band, both band centres must be either greater than 41 GHz (the point at which the conversion changes from lower side-band to upper side-band) or both less than 41 GHz. 

Observing is possible with the standard 15-mm and 7-mm systems on all six antennas, and 3-mm systems on five antennas: there is no 3mm receiver on CA06. Note that the 3mm receivers are ageing and that, as spare parts are limited, or non-existent, component failure in a receiver may not be able to be repaired in a timely manner, or at all. 

The ATCA sensitivity calculator provides a means of determining the sensitivity characteristics of observations, and can include the reduction in bandwidth expected due to RFI in the 16cm band.

Millimetre observing

Observing at 3 mm generally starts in May and ends in mid-October. Proposers are reminded that the primary flux density calibrator at 3 mm is Uranus, which in April 2025 will be near a R.A. of 3h28m and declination of +18d39m. Proposals for 3-mm observations that require accurate flux calibration should request time for observations of Uranus (if the array configuration allows). For 7-mm observations with CABB, PKS 1934-638 has sufficient flux density to be used as a primary flux density calibrator, and should be preferred over Uranus for all projects. 

Proposers requiring their own observations of Uranus (at special frequencies, or at a time when their main target has set, for example), should make this clear in the observations table and justification of their proposal. For secondary calibration at 3- and 7-mm, Observatory staff will calibrate a number of bright AGN, spread over the full range of R.A., against Uranus (at 3mm) and 1934-638 (at 7mm) at the standard continuum observing frequencies throughout the semester. 

The array is outfitted with Water Vapour Radiometers (WVRs) provided by the University of New South Wales. Experience to date indicates that these units will, in some conditions, allow corrections to the measured phases on longer baselines to be made, improving phase stability and sensitivity. Interested mm-wavelength observers will be able to use this capability during 2025OCT. Details of the system are available at the WVR webpage. 

Further information

The Australia Telescope Compact Array User Guide describes how to apply for observing time, make a schedule file, and carry out observations with the ATCA.

Target of Opportunity and NAPA (non A Priori Assignable) proposals

For further information contact the ATCA System Scientist, Jamie Stevens (Jamie.Stevens [at] csiro.au).