Introduction

The Gamma-Ray Large Area Space Telescope (GLAST) is being developed as NASA's next major space-based observatory devoted to astrophysics using high-energy gamma rays (~0.1--300 GeV). It follows upon the successful Compton Observatory EGRET instrument (1991--2000), which discovered numerous interesting sources, including a new class of gamma-ray emitting active galactic nuclei called "Blazars," and seminal observations of high-energy emssion from gamma-ray bursts (GRBs).

The GLAST mission, scheduled for launch in 2007, will include two scientific instruments: the Large Area Telescope ( LAT) and the GLAST Burst Monitor (GBM). The LAT will provide ground-breaking observations of the high-energy (20 MeV to 300 GeV) gamma-ray sky, while the GBM will provide important low-energy (10 keV to 25 MeV) context measurements of gamma-ray bursts, solar flares, and other transient sources. The measurements provided by the GBM are particularly important for the study of gamma-ray bursts in order to connect current understanding based on low-energy measurements with the practically unexplored high-energy domain. Together, the LAT and GBM promise to enable a new era of extraordinarily wide-band GRB spectroscopic measurements covering more than six decades in energy. It is likely that these measurements will uncover currently obscured mechanisms that drive the fantastically powerful GRB energy release process.

The GBM instrument is being developed by a U.S./German collaboration of gamma-ray astronomers and engineers. The instrument has significant heritage from the successful BATSE instrument on the Compton Observatory. Like BATSE, GBM consists of several gamma-ray detectors distributed about the GLAST satellite. Signals from individual detectors are collected in a central processing unit that automatically detects bursts, computes their rough direction, and records the best data.

Because GBM employs unshielded, distributed gamma-ray detectors, its sucessful operation depends on detailed knowledge of how radiation scatters into the detectors from passive materials in the detector housing, the spacecraft, and Earth's atmosphere. A small team of scientists at Los Alamos is leading the effort to model the GBM in the context of these important effects. The modeling effort is based on Monte Carlo radiation transport simulations that will be verified against a comprehensive series of experimental calibration tests.

In the end, the models and simulations will be used to produce a multi-dimensional "detector response function" that will be used in the analysis of all This site contains information, software, and data related to the collaborative GBM instrument modeling and simulation effort. In the future, simulation software tools, references, and results will be distributed through the site.