HERA has been both under construction and in operation over this current observing season, which ends in April 2018. The final numbers for the season are that 71 are in operation of 131 constructed antennas. Construction of antennas will continue apace and the signal paths will begin their retrofit beginning in May. From then through the following observing season about 200 new systems will be deployed. The final 150 systems will be deployed after next season. The new architecture was described in the last Newsletter, but to summarise, the new feeds will work from 50-250 MHz, the digitisers will get deployed in the field and the correlator will move back to the central processing building.
As described elsewhere, the potential of a detection of the global signal at around a frequency of 70 MHz (z ~ 19) amplifies the interest in the augmented range of HERA that will come on-line beginning this year. The HERA analysis teams have been carefully looking at the existing HERA data which, with an average of about 60 integration-worthy antennas, has significant sensitivity over 110-190 MHz. (An interesting issue has been dealing with the ever-increasing antenna numbers over a season).
The team in South Africa has been doing an amazing job of antenna construction and infrastructure deployment and are meeting their target build-rate. They are ramping up the procurement and deployment for the new architecture (underground reticulation and the new field-based “nodes”) to meet the delivery of the new hardware. The figure shows the current state of antenna construction (all circles) and the antennas that are hooked up to the correlator for science (71 green circles).
Cambridge University is finalising the design of the new feed and analog signal path for an April/May deployment in South Africa. In March, the first of the new feeds was deployed on the test antenna at Lords Bridge near Cambridge UK. The feed went together seamlessly and the measured performance matched predicted extremely well. With a few small “production” tweaks, the new feed will be ready for production for its initial deployment in South Africa. The new feed is funded by the Gordon and Betty Moore Foundation (as are the final 110 antennas) and MIT will help oversee the production. The first Cambridge USA versions will be tested at the Green Bank HERA test facility in May. In conjunction with these efforts, the team is finalising the node hardware and correlator.
Currently, a huge amount of effort is going into data analysis and reduction of the current HERA data. Quality assurance and calibration are huge efforts and software tools are both in place and in development to handle this. As mentioned, one interesting aspect is incorporating the pace of new antennas being ready for use and a fairly mature “graduation” process is in place. The commissioning/operations, quality and analysis teams are busy generating defined internal data release (IDR) products that can be used for power spectrum analysis. The first power spectrum pipelines are using the results of the first IDRs to refine the techniques and produce the first estimates.
HERA is a partnership to conduct an experiment to detect and characterize the Epoch of Reionization. Partner institutions in the collaboration are Arizona State University, Brown University, University of California Berkeley, University of California Los Angeles, University of Cambridge, Massachusetts Institute of Technology, National Radio Astronomy Observatory, University of Pennsylvania, Scuola Normale Superiore de Pisa, SKA-South Africa and the University of Washington. Additional collaborators are Cal Poly Pomona, Imperial College, Harvard-Smithsonian Center for Astrophysics, University of KwaZulu Natal, Rhodes University and University of Western Cape. HERA is an SKA precursor instrument. HERA is funded by the US National Science Foundation, the Gordon and Betty Moore Foundation with additional support from the partner institutions.