GLAST Large Area Telescope Performance Monitoring and Calibrations

The Large Area Telescope (LAT) is one of the two instruments onboard the Gamma ray Large Area Space Telescope (GLAST), the next generation high energy gamma ray telescope. It contains sixteen identical towers in a four-by-four grid, each tower containing a silicon-strip tracker and a CsI calorimeter that together will give the incident direction and energy of the pair-converting photon. The instrument is covered by an Anti-Coincidence Detector (ACD) to reject charged particle background. Altogether, the LAT contains more than 864k channels in the trackers, 1536 CsI crystals and 97 ACD tiles and ribbons.

The LAT was integrated and tested at the Stanford Linear Accelerator Center (SLAC) in 2005-2006, underwent Thermo-Vacuum (TVAC) testing at the Naval Research Lab (NRL) in the summer of 2006 and is currently being integrated with the Spacecraft at General Dynamics/Spectrum Astro Space Systems in Arizona. GLAST is due to be launched in Fall of 2007.

This poster details some of strategies and methods for calibrating the instrument, including both particle based calibrations, using Galactic Cosmic Rays (GCR) events, and charge injection, that will be necessary to ensure a satisfactory performance of the LAT in its full energy range from 20 MeV to 300 GeV. It will also detail how we are planning to monitor the instrument performance, including both low level detector monitoring and more high level analysis based monitoring using astrophysical sources. Both calibrations and monitoring draws on the extensive experience gained from Integration and Test of the instrument.