Gamma Ray Burst localization with GECCO’s BGO anti-coincidence shields.

Accurate localization of transient sources, which carries critical information about their nature, especially given recent discoveries of the GW and high-energy neutrino events, falls within the potential capabilities of gamma-ray telescopes. Presently, the ability for accurate localization in the MeV photon energy range is limited by measurements complications. The Galactic Explorer with a Coded Aperture Mask Compton Telescope (“GECCO”) will provide such capabilities thanks to the innovative use of a deployable coded aperture mask in combination with a Compton telescope mode. The spatial arrangement of GECCO’s thick and efficient BGO anticoincidence panels can be used to quickly estimate the localization of transient events, allowing a prompt slew of the telescope. GECCO has 8 heavy-scintillator shield panels, arranged on the instrument sides. The ratios between the counts recorded by the panels depends on the direction of the signal with respect to the telescope axis. Simulations were conducted to assess the localization capabilities of the BGO shields, simulating the detection of Gamma Ray Burst signals from the Fermi-GBM catalog with various spectral shapes and time profiles, in order to assess the evolution of their localization error radius with time. The results show how the GECCO shields can achieve localization radii of a few degrees in a short time.