The Gamma-Ray Large Area Space Telescope (GLAST) was launched by NASA on 11 June from the Cape Canaveral Air Force Station in Florida. GLAST is a next-generation, high-energy, gamma-ray observatory, designed to explore some of the most energetic phenomena in the universe and enhance knowledge of fundamental physics, astronomy and cosmology. It is an international, multi-agency mission with important contributions from research institutions in France, Germany, Italy, Japan, Sweden and the US.
GLAST will capture high-energy gamma rays (from 20 MeV to greater than 300 GeV) from a wealth of cosmic sources that are sites of very-high-energy particle acceleration. These include the supermassive black hole systems of active galactic nuclei, supernova remnants, neutron stars, galactic and solar system sources, and gamma-ray bursts (GRBs). The GLAST collaboration expects to discover thousands of new sources of different classes, which will shed light on many unresolved questions about the nature of dark matter, the origin of cosmic rays, the engines of GRBs, and acceleration mechanisms of high-energy cosmic particles. The discoveries may also provide tests of fundamental physical principles, such as Lorentz invariance.
Image credit: NASA/Jim Grossmann.
The Large Area Telescope (LAT) is the main instrument on board (Michelson 2008). It is accompanied by the Gamma-Burst Monitor (GBM), an instrument primarily dedicated to the detection of GRBs between 8 keV and 30 MeV (von Kienlin et al. 2001). Together the GBM and LAT will cover a remarkable seven decades in energy.
The LAT is a pair-conversion telescope that measures the direction, energy and arrival time of incoming photons from the entire sky with unprecedented resolution and sensitivity. It will collect more than two orders of magnitude more gamma rays than its predecessor, EGRET (Thompson et al. 1993), and the current gamma-ray mission AGILE (Tavani et al. 2008). This leap in capabilities is made possible by combining information from three detector subsystems, all based on major developments in experimental particle physics. These are a silicon-strip tracker-converter, the largest of its class with its 70 m2. of active surface and 900,000 digital channels; an 8.5 radiation-length CsI imaging calorimeter, capable of a very large dynamic range to ensure better than 15% energy resolution over the entire acceptance; and an outer, segmented plastic scintillator anticoincidence shield, which is used to reject charged particle background.
Teams in the participating institutes built and qualified the LAT subsystems for space before they were integrated at SLAC. The Max Planck Institute for Extraterrestrial Physics in Garching produced the GBM detectors, and these were integrated at the Marshall Space Flight Center in Huntsville. Both instruments were then integrated with the spacecraft at General Dynamics, in Phoenix, Arizona, to form the GLAST observatory. Environmental testing took place both at General Dynamics and at the Naval Research Laboratory in Washington DC. The calibration of the LAT relies on a combination of charge injection, ground and in-orbit cosmic-ray data, an advanced Monte Carlo simulation based on the Geant4 toolkit, and data from particle test beams collected from a calibration unit at CERN and GSI (Baldini et al. 2007).
Further reading
For more about GLAST see www.nasa.gov/glast.
P Michelson et al. (in preparation).
A von Kienlin et al. 2001 ESA SP 459 529.
D J Thompson et al. 1993 ApJS 86 629.
M Tavani et al. 2008 NIM-A 588 52.
L Baldini et al. 2007 AIP Conf. Proc. 921
