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Paper: A High Performance Spatial Query Engine for Large Event Data Sets Developed for the GLAST LAT Instrument
Volume: 376, Astronomical Data Analysis Software and Systems XVI
Page: 26
Authors: Stephens, T.
Abstract: The Large Area Telescope (LAT) is the primary instrument onboard the Gamma-ray Large Area Space Telescope (GLAST) satellite. The LAT is not a typical imaging instrument but rather records the energy and arrival direction of each individual gamma-ray photon. It is designed to operate primarily in sky survey mode, instead of pointing at fixed targets for long periods of time. The standard survey mode gives complete coverage of the celestial sphere every 2 orbits (~3 hrs). Additionally, the LAT has a very large (~2 sr) field of view, and an energy dependent point spread function (PSF). These factors combine to generate a large data volume and present a unique challenge in providing data to the user community for the study of astronomical sources.

We present the design of the public data server at the GLAST Science Support Center (GSSC) for the LAT data as well as performance benchmarks of the initial implementation. The data server operates on event lists stored in FITS files. Based on the userís query, the photons matching the data cuts are extracted and presented to the user as a FITS file ready to be downloaded and used in the GLAST science analysis software. Running on a single CPU, the photon data server can extract and prepare the ~1.5 million photons matching a typical userís query from the ~80 million photons in a yearís worth of observational data in approximately 40 s. The complete system is implemented as a small cluster of Linux PCs to improve performance even more by distributing the load of a single query or processing multiple queries simultaneously.

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