The Long Baseline Array (LBA) uses the Australia Telescope Compact Array and the Murriyang and Mopra radio telescopes, together with the Hobart and Ceduna and the AuScope Yarragadee and Katherine 12-m antennas operated by the University of Tasmania. Use of the Warkworth Observatory 12m and 30m antennas, now operated by SpaceOps NZ, may be possible around their other commitments. 

The Warkworth 12m can observe at 13 and 3cm, and the Warkworth 30-m telescope can observe at 6.7 and on a best-efforts basis at 4.8 and 8.4 GHz: these can be requested but their availability cannot be guaranteed. The Hartebeesthoek 26-m or 15-m telescopes may also be available. All telescope availability is subject to other commitments – scheduling is done on a best efforts basis.

A limited amount of time may be available with the Tidbinbilla 70-m antenna or one of the 34-m antennas. 

ASKAP is not presently available for VLBI. The AuScope antennas have wideband 2–14 GHz receivers. During the 2026APR semester, some LBA time may be scheduled at the same time as a European VLBI Network (EVN) session, opening the possibility of joint LBA/EVN observations. The easternmost stations of the EVN are in a similar longitude range to the LBA telescopes, and for sources in equatorial regions, baselines to western European stations are also achievable. Proposals for joint LBA/EVN observations must be submitted separately to both the LBA and EVN at their respective deadlines. Similarly, co-observing with the East Asian VLBI Network is possible, via proposals to both networks. 

As a result of the BIGCAT upgrade for ATCA, during observations with the VLBI tied array it will be possible to record data in the standard ATCA continuum mode at the same time.  

Constraints on Murriyang receiver changes impose limits on the frequency of LBA observations with Murriyang. Observations at frequencies higher that 4 GHz  will entail removing the UWL or CryoPAF from the focus cabin. This is unlikely to be done more than once per semester. Observations with Murriyang at 8.4 and 22 GHz may be possible: other frequencies may be requested but are less likely and will be available less frequently. 

The Murriyang UWL and AuScope Katherine, Hobart and Yarragadee telescopes produce linear polarisations, which are converted to circular polarisations post-correlation, usually with reasonable results.

LBA proposers are reminded that a member (or members) of the proposal team will be required to assist with the VLBI observing on the ATNF telescopes. Please ensure that a member of the proposal team will be able to help. Note that due to logistical constraints the VLBI schedule usually is released only a few weeks before observing, so the observer will need to be qualified for remote observing with Murriyang and ATCA. New observers are able to be trained remotely prior to the LBA session.

Telescopes outside the core LBA may be also requested for special observations. Specific system availability may be dependent on availability at individual antennas. Sources close to the equator may benefit from including telescopes from Asia. No formal mechanism is currently available for requesting time and all such telescopes need to be negotiated on a case-by-base basis. Phil Edwards can assist with this process.

For more details, please refer to the Long Baseline Array and pages thereunder.

Potential first-time users have a Novices Guide available to them from the VLBI webpage.

Proposers can use the EVN planning tool, which includes the LBA telescopes. Proposers may also contact Phil Edwards (details below) with any questions related to sensitivity calculations for LBA observations.

The current capabilities of the LBA are briefly outlined below:

• The disk-based recording system is used for all recorded VLBI observations and data rates (up to 1 Gbps) can be achieved at most stations.
• All recorded observations will be correlated with the DiFX software correlator. The software correlator is capable of correlating the high data rate observations at high spectral resolution with arbitrary correlator integration times.

User support is available, including assistance with proposal preparation, scheduling, observer training and data reduction.

A bit rate of 256 Mbps (2x16MHz bandwidth in 2 polarisations, with 2 bit digitisation and Nyquist sampling) can be sustained at all LBA telescopes and is the standard observing mode. Observations requesting higher bit rates will need to include a clear justification for the requested rate. Potential users must consult the VLBI National Facility Upgrade capabilities.

Commensal wide-field correlation of LBA data 

A paper was submitted to the Australia Telescope User Committee (ATUC) in advance of its October 2024 meeting proposing that low-frequency (20cm and 13cm band) LBA data — excluding the original LBA proposer’s target(s) of interest — be used for wide-field correlation at potential VLBI targets determined from surveys being undertaken with SKA pathfinders and precursors. In its report to the ATNF, ATUC endorsed this proposal (see https://www.atnf.csiro.au/management/atuc/2024Oct/ATUC-2024OCT-submitted.pdf).

The DiFX correlator, used for LBA data correlation, allows efficient correlation at multiple phase centres in a single pass. This means that good use can be made of data over a much wider field of view than required for the proposing team’s science. This would allow the detection and characterisation of AGN within the field of view, and support searches for compact calibrator sources for use in the SKA-VLBI era. The proposal, led by Jack Radcliffe and Jordan Collier, proposes that the LBA conducts multi-phase-centre correlation (excluding the target region(s)) for LBA observations in the 20cm and 13cm band (i.e., frequencies below 3 GHz).  The data from these wide-field observations would be made publicly available in a timely manner following the correlation as a service to the community.  An option to “opt out” of this will be provided on the LBA cover sheets, though proposers will be asked to provide a justification for why they do not want fuller use to be made of their data. We anticipate that a default “exclusion radius” around the pointing position will be defined, but that users will be able to designate an alternative exclusion zone where a justification exists. The PIs of observations at frequencies below 3 GHz will be contacted individually to define the exclusion zone(s) for the wide-field correlation. More details will be made available from the LBA webpage — https://www.atnf.csiro.au/facilities/long-baseline-array/ . 

For more information contact the LBA System Scientist, Phil Edwards (Philip.Edwards [at] csiro.au).