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Paper: A High-performance Spatial Query Engine for Large Event Data Sets Implemented for the Fermi LAT Data
Volume: 411, Astronomical Data Analysis Software and Systems XVIII
Page: 197
Authors: Stephens, T.E.
Abstract: The Large Area Telescope (LAT) is the primary instrument onboard the Fermi Gamma-ray Space Telescope (Fermi). 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 hours). 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 Fermi Science Support Center (FSSC) for the LAT data as well as performance benchmarks of the initial flight implementation. The data server operates on event lists stored in FITS files. Based on the user’s 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 Fermi science analysis software. Running on a single CPU, the photon data server can extract and prepare the 3-4 million photons matching a typical user’s query from the ~120 million photons in a year’s worth of observational data in approximately 20 seconds. 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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