July 1, 2025Open Access

The Detector Design of the Southern Wide-Field Gamma-Ray Observatory

Key Points

The observatory aims for high sensitivity to gamma rays and cosmic rays, enhancing detection capabilities in the southern hemisphere.
A proposed sensitive area of 0.3 km2 aims to extend to 1 km2 at high altitudes above 4400m, maximizing gamma ray measurements.
The design employs water Cherenkov detector technology focusing on efficient gamma-hadron discrimination and operational efficiency during daylight.
Optimized detector layout increases performance at lower costs, ensuring excellent angular resolution across energies, particularly in the PeV range.

Abstract

Abstract The Southern Wide-Field Gamma-Ray Observatory (SWGO) observatory will use water Cherenkov detector (WCD) technology to construct a large-area, high-altitude observatory to measure gamma and cosmic rays’ energy and arrival direction. The proposed observatory will have a sensitive area of approximately 0.3 km2 with possible extensions to 1 km2 and be located at a high altitude (>4400m) between 14 degrees and 24 degrees south latitude. The high altitude of the observatory facilitates the detection and measurement of gamma and cosmic rays by placing the detector well into their extensive air shower (EAS) for energies down to several hundred GeV. The large detector area provides significant sensitivity to energies into the PeV range. The location in the southern hemisphere offers a view of sources in the southern sky, including the Galactic Center. WCDs can be operated during daylight, continuously monitoring the overhead sky, enabling coverage of a large fraction of the sky. The detector design also seeks to optimize gamma-hadron discrimination to distinguish the gamma-ray-induced EAS from those induced by the far more numerous cosmic rays. The reference design utilizes double-chamber WCD detector units. The larger volume of the WCD’s upper compartment provides calorimetry and timing information for the electromagnetic component of the EAS. The lower compartment will be used for muon tagging to aid in the rejection of muon-rich hadronic showers. The array layout of the individual WCDs is optimized to provide the best performance at the lowest cost. Excellent sensitivity and gamma-hadron separation over a wide range of energies with good angular resolution will be achieved by varying detector unit spacing, with a dense inner core and an outer region populated at a lower density. This proceeding will describe the research and development program for mechanical design, photosensors, readout electronics, and data-acquisition systems to produce the optimal detector for SWGO.

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