The Fermi Gamma-ray Space Telescope (FGST or Fermi) is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Originally called the Gamma-Ray Large Area Space Telescope, or GLAST, the mission was renamed for the physicist Enrico Fermi after its launch aboard a Delta II 7920-H rocket from Cape Canaveral in Florida in 2008. The mission is a joint venture of NASA, the United States Department of Energy and agencies and institutes in France, Germany, Italy, Japan, and Sweden.
Fermi's main instrument is the Large Area Telescope (LAT), which is used to perform a continuous all-sky survey to study astrophysical sources of high-energy emission such as active galactic nuclei, pulsars, other cosmic particle accelerators, and to search for signatures of dark matter annihilation or decay. The LAT is an imaging high-energy gamma-ray telescope covering the energy range from 20 MeV to more than 300 GeV. The LAT's field of view covers about 20% of the sky and the instrument scans whole sky every three hours. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM), is being used to study transient gamma-ray phenomena such as gamma-ray bursts.
The LAT was constructed at the SLAC National Accelerator Laboratory, with contributions from the partner institutions of the LAT collaboration. The LAT collaboration includes more than 400 scientists and students at more than 90 universities and laboratories in 12 countries. Professor Peter Michelson of Stanford University is the Principal Investigator and spokesperson for the collaboration. The collaboration has published papers on pulsars, active galactic nuclei, the extragalactic background light, globular clusters, cosmic-ray electrons and positrons, gamma-ray bursts, binary stars, supernova remnants, galactic novae, diffuse gamma-ray emission, solar flares, indirect searches for dark matter and other subjects. Because of their all-sky monitoring capability, the LAT and GBM are on the front lines in searches for electromagnetic counterparts of LIGO/VIRGO gravitational wave events triggered by merging black hole and neutron star systems.
The SLAC National Accelerator Laboratory also hosts the LAT Instrument Science Operations Center, or ISOC, which is managed by SLAC staff scientist and KIPAC member Dr. Robert Cameron. ISOC operates the LAT for the Fermi mission in cooperation with the Fermi Mission Operations Center and the Fermi Science Support Center, both at NASA's Goddard Space Flight Center.
The principal functions of the ISOC are:
• to monitor the functionality and safety of the LAT by monitoring and trending its engineering telemetry
• to construct all routine and special LAT commanding to ensure its continued correct operation and maintain its continuous data collection
• to maintain the embedded software in the LAT and update it as needed
• to verify and optimize its science performance
• to receive, archive and process raw event data transmitted from Fermi to the ground several times per day
• to perform event reconstruction processing on the raw LAT science data
• to deliver processed photon data to NASA for immediate public release
• to archive and host processed LAT event data (photon and non-photon) for the LAT collaboration
• to perform automated science processing of the photon data to refine prompt results on known or detected gamma-ray bursts
• to monitor and report light curves for selected celestial gamma-ray sources
• to search for and report light curves for flaring celestial gamma-ray sources
• to develop and maintain science analysis tools for use by the LAT collaboration and the broader science community
• to maintain the data processing, storage and access infrastructure for the LAT collaboration.
The ISOC makes use of the large-scale computing capabilities at SLAC, routinely using up to 2000 computer cores for data processing, with over 1 Petabyte of data archived and available.
This image shows a cutaway view of the Large Area Telescope (LAT) on Fermi. An incoming gamma-ray photon (shown in red) will convert to an electron-positron pair of particles (shown in blue) in the LAT, typically in one of the 16 Tracker towers, each of which consists of 36 layers of Silicon strip charged-particle detectors, interleaved with Tungsten layers. Below each Tracker Tower is a Calorimeter module to measure the energy of charged electron and positron. The LAT has 16 towers consisting of stacked Tracker and Calorimeter modules, arranged in a 4x4 grid. Surrounding these is a tiled Anti-Coincidence Shield, which allows the LAT to detect and discriminate against incoming charged particles.
This image shows the LAT gamma-ray brightness map of the entire sky in Aitoff projection. This is a 9-year dataset collected between August 2008 and August 2017. About 6 million photons with energies above 1 GeV and well-measured directions are included in the image. The colors in the image represent brightness, from blue (lowest flux) through red to yellow (highest flux). The image is in the Galactic coordinate system, and clearly shows the plane of our Galaxy stretching across the middle of the image, plus many compact sources off the Galactic plane, which are typically pulsars in the Milky Way or distant active galaxies called blazars, together with diffuse extragalactic emission filling the sky.