The U.S. teams involved in the development of the CTAO have been awarded a $3.9 million grant from the National Science Foundation (NSF) to contribute to building and installing ten cameras for the Small-Sized Telescopes (SSTs). Led by the Washington University in St. Louis and the University of Wisconsin–Madison, the funds will provide light detectors for the telescopes located on the CTAO-South site in Chile, as well as the readout and control electronics required to operate them.
The SSTs are the smallest of the CTAO’s three telescope types that the Observatory will use to cover its broad energy range, from 20 GeV to 300 TeV. They will outnumber the other telescopes, with 37 SSTs planned in the approved Alpha Configuration and spread across several square kilometres on the CTAO-South array. Their large collection area makes them essential for extending CTAO’s sensitivity to the highest TeV energies, enabling study of the most energetic cosmic accelerators in our Galaxy.
“By detecting light trillions of times more energetic than what we can see with our eyes, the CTAO will discover energetic phenomena powered by black holes and exploding stars,” says Justin Vandenbroucke, Professor at the University of Wisconsin–Madison and co-lead of the NSF project. “The SSTs of CTAO-South will have a particularly good view of the inner Galaxy, where these phenomena are abundant.”
The SST’s design permits a compact camera based on silicon photomultiplier (SiPM) sensors. Each camera’s 32 SiPM tiles account for a total of 2,048 pixels, covering a large field of view of approximately 9 degrees. The camera records Cherenkov light in 128-frame movies, with each frame lasting one billionth of a second.
With the new NSF funds, the CTAO-US teams will become significant contributors to the CTAO SST Collaboration, the In-Kind Contributors responsible for building this class of telescopes. The development and installation of these ten cameras will enhance the Observatory’s capabilities at the highest energies and marks a significant step in the U.S. teams’ participation in the project.
“We are excited to make a significant contribution to the CTAO by providing camera instrumentation for the SSTs in the southern array,” says Manel Errando, Assistant Professor at Washington University in St. Louis and co-lead of the NSF project. “This effort not only brings the CTAO closer to the completion of construction but also secures a pathway for US-based scientists to participate fully and gain access to CTAO data.”
The U.S. members have been deeply involved in the CTAO project since its inception more than a decade ago, contributing across governance, scientific, and technological domains. “The U.S. teams have been an important supporter of the CTAO throughout its history,” said CTAO Director General, Stuart McMuldroch. “We are grateful for their various contributions and look forward to continuing and expanding our work together in this new phase.”
They participated as an Observer in the CTAO gGmbH, the former legal entity of the Observatory prior to the establishment of the ERIC in January 2025. Negotiations regarding U.S. accession to the ERIC are currently ongoing. Additionally, the CTAO-US teams have been active members of the CTAO Consortium, the group dedicated to the science exploitation of the Observatory, holding key managerial positions, including that of Co-Spokesperson.
They are also engaged through In-Kind Contribution collaborations, with a particular focus on the design of an alternative structural configuration for the Medium-Sized Telescopes, known as Schwarzschild-Couder Telescope (SCT), featuring an innovative dual-mirror optical system. This optical design was first conceived by CTAO-US members in 2006, and a prototype was inaugurated in 2019 at the Whipple Observatory in Arizona. New funds will now enable them to build cameras for the SST, which incorporate the same dual-mirror optical system, and a very similar camera design featuring many of the same components, as the SCT.