2009ApJ...702..791M

The Gamma-Ray Burst Monitor (GBM) will significantly augment the science return from the Fermi Observatory in the study of gamma-ray bursts (GRBs). The primary objective of GBM is to extend the energy range over which bursts are observed downward from the energy range of the Large Area Telescope (LAT) on Fermi into the hard X-ray range where extensive previous data sets exist. A secondary objective is to compute burst locations onboard to allow re-orienting the spacecraft so that the LAT can observe delayed emission from bright bursts. GBM uses an array of 12 sodium iodide scintillators and two bismuth germanate scintillators to detect gamma rays from ∼8 keV to ∼40 MeV over the full unocculted sky. The onboard trigger threshold is ∼0.7 photons/cm2/s (50-300 keV, 1 s peak). GBM generates onboard triggers for ∼250 GRBs per year.