GALI -- A GAmma-ray burst Localizing Instrument: Results from Full Size Engineering Model

Abstract

We present a full-size engineering model of GALI - The GAmma-ray burst Localizing Instrument, composed of 362 CsI(Tl) small cubic scintillators, distributed within a small volume of $\sim2$l, and read out by silicon photo-multipliers. GALI can provide directional information about GRBs with high angular accuracy from angle-dependent mutual obstruction between its scintillators. Here, we demonstrate GALI's laboratory experiments with an $^{241}$Am source, which achieved directional reconstruction of $<$3$^\circ$ accuracy, in agreement with our Monte-Carlo simulations. GALI has a wide field view of the unobstructed sky. With its current cubic configuration, GALI's effective area varies between 97 cm$^2$ (face on) and 138 cm$^2$ (from the corners at 45$^\circ$), which is verified in the current experiment.