HIRAX Correlator to Enable New Cosmological Discoveries

The development of the Hydrogen Intensity Real-time Analysis eXperiment (HIRAX) Correlator, a new component to the HIRAX radio interferometer is set to bring cosmologists one step closer to conducting ground-breaking science experiments in the field of dark energy and Fast Radio Bursts (FRB’s).

The HIRAX radio interferometer of closely packed 6m dishes observing between 400 and 800 mHz is currently funded up to 256 dishes with a possible future expansion to 1024 dishes. The array will be co-located with the Square Kilometer Array at the MeerKAT radio telescope site which is operated by South African Radio Astronomy Observatory (SARAO) in the Karoo, South Africa.

The Swiss partners at ETH Zürich (ETH-Z) and Université de Genève (UniGe) have spent the last two years developing the HIRAX correlator with HIRAX partners at the University of KwaZulu-Natal (UKZN) and the University of Toronto UofT. This is a significant component of the cutting-edge HIRAX instrument, which consists of custom hardware and software. As the name suggests, the HIRAX correlator cross-correlates the signals from all telescopes forming visibilities. This is the fundamental data product of a radio telescope, which will be stored as the raw dataset for cosmology and map-making purposes. The correlator will be installed onto the HIRAX 256-dish array.

Professor Kavilan Moodley, the HIRAX Principal Investigator and Professor at UKZN said: “HIRAX is a truly international astronomy project with key partners across the globe contributing to the development of the instrument.”

Correlator engineer, Mr Thierry Viant explained: “The correlator system is calibrated to receive large volumes of incoming data from the dishes. It is built using a graphics processing unit (GPU’s) board cluster, which is transmitted to 8 supercomputers.  Each computer is equipped with 1 terabyte (TB) of memory, 2 GPU’s for correlation computing, and 4 network interface boards to receive data inputs. We have received credible results using the dedicated astronomical software, Kotekan built by UofT.”

HIRAX completed its Radio Frequency Interference (RFI) testing of the HIRAX correlator at the European Laboratory for Nuclear Research and Particle Physics (CERN) in Switzerland this year.

The collaboration is led out of UKZN with seven additional South African consortium members and 17 international partners. The project is currently funded by the South African Department for Science and Innovation (DSI) and National Research Foundation (NRF), the HIRAX South African Consortium, McGill University in Canada, and a partnership of Swiss universities with funding from the SNF.

Before shipment to the HIRAX site, the correlator needed to undergo Radio Frequency Interference (RFI) testing. RFI is when unwanted radio frequencies are detected in the data collected from a radio instrument, which can easily make collected visibilities unusable. RFI can be emitted by any man-made device with a capacity to produce signals in the radio band; including, cellphones, microwaves, and even an instrument’s own hardware.

The MeerKAT radio telescope site is radio-controlled, with strict regulations to ensure that the hosted instruments are protected from RFI. Because HIRAX is a guest instrument on the SARAO site, sharing space with several other radio astronomy projects including MeerKAT, HERA, and eventually the SKA, it is important that HIRAX not only protects its own data from RFI but is also a good neighbour to others. To ensure this, all HIRAX instrumentation will be subjected to strict RFI testing to determine if shielding or other mitigation tactics are needed to protect the site’s low-RFI environment.

Mr Roufurd Julie, SARAO Guest Instrument Manager, commented on the RFI environment at SARAO: “By sharing a location with MeerKAT, HIRAX will be able to conduct science in an area where radio frequency interference is tightly controlled, a move that has seen MeerKAT producing ground-breaking scientific discoveries since its launch three years ago.” Professor Daniel Valuch from CERN commented on the HIRAX correlator testing, saying: “No two problems we had been following so far by our ElectroMagnetic Compatibility (EMC) lab were the same. We are typically looking at very specific and obscure problems deep in the accelerators – such as pulsed signals, cable interactions, low-frequency fields, high-frequency fields, perturbation to ultra-precise devices, and particle beams. Measuring the RF emissions from the HIRAX correlator, a powerful computing system, was definitely a great and interesting new experience for our small EMC laboratory.”