Energy Range
∼30 keV – ∼2 MeV
A suite of 12 CsI(Tl) detectors provide an ultra-wide field of view of the unocculted sky (8 steridian). Each large-area detector panel was a 150 mm × 150 mm, 10 mm thick crystal, with a 1 × 21 array of 6 mm × 6 mm SiPMS used to read out the thin edge of the crystal. The SensL J-series SiPMs were flight-proven on the SIRI-1 mission. The individual detectors were arranged in bi-packs, arranged in pairs along the &plusnm;x and y axis, and with four on the +z (zenith-facing) side. The outward facing side of each panel had a thin aluminum window while the crystal was backed with a steel and tantalum shield which attenuated gamma rays below ∼300 keV to stop photons entering the rear-facing side. Localization of bursts by maximum likelihood algorithms provided typical localization of <5° (compared to 10° for comparable sGRBs with Fermi GBM) and roughly twice Fermi GBM’s effective area with a typical sGRB spectrum. This expanded the horizon for faint objects in the local Universe by ∼1.4 (and thus encompassed roughly 3 times Fermi GBM’s detectable volume of space).
