Fermi Gamma-ray Space Telescope Overview

Large Area Telescope (LAT)

The primary instrument is the Large Area Telescope (LAT) which is a pair conversion telescope operating in the ~20 MeV to >300 GeV band. It has superior area, angular resolution, field of view, and deadtime, provide a sensitivity increase of a factor of 30 times over previous instruments in the high-energy gamma-ray band. The LAT's field of view and sensitivity make it a key instrument for studying phenomena on timescales from milliseconds to years. The instrument contains three subsystems, the tracker, calorimeter, and anti-coincidence detector, which work together to detect and characterize high-energy gamma rays. Each subsystem functions as a complex instrument with independent requirements for monitoring, analysis, and calibration. Instrument performance metrics were characterized just after launch and after 10 years on orbit. The LAT was developed by an international collaboration with partner institutions in the United States, France, Italy, Japan, and Sweden.

Further information is available on the FSSC's LAT page.

Gamma-ray Burst Monitor (GBM)

The Gamma-ray Burst Monitor (GBM) is comprised of 12 NaI and 2 BGO scintillator detectors providing continuous coverage of the entire unocculted sky from 8 keV to 40 MeV. It is most sensitive to transient sources including gamma-ray bursts, solar flares, and terrestrial gamma-ray flashes. When a significant rate increase is detected, the instrument initiates a trigger, and the flight software performs on-board localization and classification (GRB, solar flare, soft gamma-ray repeater, etc.) and transmits data to the ground in real time to enable quick-look science operations and rapid dissemination of burst parameters for follow-up observations. The GBM is a collaboration between NASA-Marshall Space Flight Center (NASA-MSFC) and the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany.

Further information is available on the FSSC's GBM page.

The Fermi Gamma-ray Space Telescope, originally designated the Gamma-ray Large Area Space Telescope (GLAST), launched on June 11, 2008, from Cape Canaveral. Fermi is a collaborative mission between NASA, the U.S. Department of Energy, and institutions in France, Germany, Japan, Italy, and Sweden, with the spacecraft built by General Dynamics. Following a two-month checkout phase, the mission was renamed to honor physicist Enrico Fermi on August 26, 2008, and began its first observation cycle. Within the initial weeks of operations, Fermi detected its first gamma-ray bursts and blazars, demonstrating the capabilities of its two primary instruments: the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). By early 2009, the mission began releasing data products and analysis tools to the scientific community, making LAT and GBM data publicly available to researchers.

The mission's early years yielded several significant discoveries in high-energy astrophysics. In 2010, Fermi observations revealed large-scale structures extending approximately 50,000 light-years above and below the galactic center, subsequently termed the "Fermi Bubbles." During this period, Fermi released successive source catalogs (1FGL in 2010, 2FGL in 2011) that substantially expanded the catalog of known gamma-ray sources. Additional findings included the detection of gamma-ray emission from classical novae in 2014, the identification of transitional millisecond pulsars as transient gamma-ray sources, and observations of terrestrial gamma-ray flashes associated with thunderstorms. These results demonstrated the mission's capability to study phenomena ranging from extragalactic sources to terrestrial atmospheric processes.

Fermi has demonstrated considerable technical resilience and adaptability throughout its operational history. The mission transitioned to extended operations in 2013 and has received multiple extensions through NASA senior reviews in 2012, 2014, 2016, 2019, 2022 and 2025. In 2018 the survey strategy was updated to continue all-sky observations despite a loss on rotation of one of the two solar arrays. The mission has also implemented significant improvements to its data processing capabilities, releasing Pass 7 data in 2011, Pass 8 data in 2015 with enhanced sensitivity and angular resolution, and subsequent refinements.

Fermi has played a significant role in the development of multi-messenger astronomy. In 2017, the GBM detected GRB 170817A in temporal coincidence with the gravitational wave event GW170817 from merging neutron stars, establishing the first direct electromagnetic counterpart to a gravitational wave detection. In 2018, Fermi observations contributed to identifying the blazar TXS 0506+056 as a probable source of high-energy neutrinos detected by IceCube. In 2019, Fermi detected GRB 190114C, which became the first gamma-ray burst confirmed to emit teraelectronvolt (TeV) photons. In October 2022, Fermi observed GRB 221009A, an exceptionally energetic burst. By 2020, the GBM had exceeded the detection record of the BATSE instrument aboard the Compton Gamma Ray Observatory, and by 2022, the LAT had delivered over 1.5 billion photons to the scientific community for analysis.

After more than 17 years of operations, Fermi continues to conduct all-sky surveys approximately every three hours, monitoring for transient events and long-term source variability. The mission has released multiple iterations of its primary all-sky catalog, with the 4FGL catalog reaching its fourth data release (4FGL-DR4) in 2023, incorporating 14 years of observations. The mission has also produced specialized catalogs covering pulsars, high-energy sources, gamma-ray bursts, and various transient phenomena. Fermi continues to serve as an active observational facility for the astrophysics community. Its continuous monitoring capability and rapid alert distribution system support multi-wavelength and multi-messenger astronomy campaigns, extending the mission's scientific productivity well beyond its original five-year design life.

For a list of science milestones, data and software releases, and operations events, see Mission History .

Fermi teams and Fermi science results have received numerous awards recognizing groundbreaking contributions to gamma-ray astronomy, astrophysics, and our understanding of the high-energy universe. Notably, Fermi-related research has been honored with the Bruno Rossi Prize multiple times, reflecting the mission's sustained impact on high-energy astrophysics. These honors celebrate the mission's transformative role in advancing multimessenger astronomy and fundamental physics. Below is a summary of notable awards received by Fermi team members and collaborations.

The Fermi Project is composed of several groups that work together to deliver Fermi data to users. See Operations for more details about what they do and Contacts for key points of contact for mission leadership, multiwavelength coordination, and community support.

Name	Role	Location
The Mission Operations Center (MOC)	The MOC 'cleans up' the telemetry downlinked from Fermi, monitors the health of the spacecraft, and transmits the appropriate telemetry to the other ground system elements. The MOC also sends commands to the spacecraft, particularly a weekly load of observing and operational commands based on timelines created by the instrument teams and the FSSC.	NASA-Goddard Space Flight Center, Greenbelt, MD
LAT Instrument Science Operations Center (LISOC)	The LISOC receives the 'cleaned up' telemetry, monitors the LAT through the housekeeping portion of the telemetry, processes the science data, and transmits the resulting science data products to the FSSC. The LAT science data processing is quite extensive, starting with event reconstruction from the 'hits' in different parts of the LAT and ending with a characterization of these events.	SLAC National Accelerator Laboratory, Palo Alto, CA
GBM Instrument Operations Center (GIOC)	The GIOC receives the 'cleaned up' telemetry, monitors the health of the GBM, processes the science data, and transmit the resulting science data products to the FSSC. The GIOC also produces automated alerts (e.g., for gamma-ray burst) and detailed event descriptions that are disseminated quickly to the scientific community for follow-up observations with other telescopes.	National Space Science and Technology Center, Huntsville, AL
Fermi Science Support Center (FSSC)	The FSSC provides provides data access to the science community, develops and maintains analysis software and documentation, creates the observing timeline, and organizes the Guest Investigator Program.	NASA-Goddard Space Flight Center, Greenbelt, MD

Two independent groups are also important parts of the Fermi Project. See Community and Collaboration for more information about their activities.

Name	Description
LAT Collaboration	An international team of scientists responsible conducting gamma-ray research, publishing scientific findings, and providing resources for the broader astrophysics community.
Fermi Users Group (FUG)	An external advisory group representing the astrophysics community that serves as the primary interface between the user community and Project in preparation for Senior Reviews. FUG meetings are a forum for the Guest Investigator (GI) community to provide feedback on the FSSC and the Instrument Teams with respect to the planning and execution of Fermi operations.

Fermi operates primarily in an all-sky scanning survey mode. This means that the LAT rarely stares at a single point in the sky. Rather, the LAT continuously scans the sky, alternating between the northern and southern hemispheres each orbit. This strategy provides 30 minutes of observing on each point in the sky every two orbits (approximately three hours). The GBM sees the entire unocculted sky.

The FSSC checks for conflicts between instrument commanding parameters ingested from the instrument operations centers, coordinates needed adjustments, and then forwards timelines to the MOC for validation. In addition to setting the overall spacecraft attitude profile and coordinating the instrument commanding, the FSSC plans the weekly sequence of LAT instrument commands, including calibrations and configuration changes.

Data from Fermi is downlinked via the Tracking and Data Relay Satellite System (TDRSS) approximately 12 times per day to ground stations. The Mission Operations Center (MOC) processes the downlinked data to ensure its integrity and usability. The MOC verifies the completeness of datasets and performs initial checks for errors or anomalies in the raw data received from Fermi's instruments. After confirming the data is reliable and addressing any issues, the MOC forwards the raw data to instrument operations centers.

At the LAT Instrument Science Operations Center, the approximately 1000 CPU processing pipeline reconstructs the energy and direction of each event and classifies them as cosmic rays or gamma rays of various qualities. The pipeline orchestrates complex data processing, splitting raw data into multiple pieces for parallel processing before reassembling and verifying the output. The pipeline also initiates automated analysis processes to find or refine positions of GRBs, monitor and deliver light curves of selected sources, and search for transient sources over the entire sky. On-call scientists follow up on flaring and transient sources daily with refined analyses and, as appropriate, initiate multiwavelength campaigns and issue alerts for GRBs, flaring blazars, gravitational wave events, high-energy neutrino counterparts, and other transients. LAT instrument data processing is the most complex and CPU intensive of any operating NASA Astrophysics mission , accomplished using the high-throughput computing facility at SLAC with approximately 5 PB of data storage and dozens of supporting servers and web applications.

At the GBM Instrument Operations Center, a GBM duty scientist supplements an automated pipeline, confirming event classification and sending out alerts as needed. During LIGO-Virgo-KAGRA observing runs, the GIOC promptly releases joint analysis results to the community, and automated processing responds to neutrino alerts and alerts from other gamma-ray instruments. On-board detections produce alerts distributed publicly via the General Coordinates Network (GCN) within seconds, with real-time quicklook data processed and delivered to the public within 10 minutes. Full resolution science data and continuous high-resolution data are downlinked every few hours for processing and public release.

Once processed, the data is delivered to the Fermi Science Support Center (FSSC) and made publicly available immediately through High Energy Astrophysics Science Archive Research Center (HEASARC). LAT data are typically accessible within 8 hours of onboard collection, while GBM science data are usually available within a few hours.

See Operations pages for more information about the ground system and the The Observatory for information about Fermi observation types, timeline, and current observations.

Fermi's contributions to astrophysics are extensive. It has detected thousands of previously unknown gamma-ray sources, dramatically expanding the catalog of extreme cosmic objects including pulsars, blazars, and supernova remnants. Fermi has provided crucial insights into gamma-ray bursts, the most powerful explosions in the universe, revealing details about their structure and emission mechanisms. The observatory has also advanced our understanding of active galactic nuclei powered by supermassive black holes, mapped the gamma-ray emission from our Milky Way galaxy, and placed important constraints on dark matter models by searching for predicted gamma-ray signatures. Additionally, its role in multi-messenger astronomy has been pivotal, linking observations across different astronomical phenomena to provide a more complete picture of the universe. Its continuous all-sky monitoring capability has enabled time-domain astronomy in gamma rays, catching transient events and revealing the dynamic, violent nature of the high-energy universe in ways that weren't possible before its mission.

The Fermi uniquely observes ~8 decades of the electromagnetic spectrum, with its instruments collectively covering energies from about 8 keV up to over 300 GeV. The Large Area Telescope (LAT) observes higher-energy gamma rays from 20 MeV to beyond 300 GeV, while the Gamma-ray Burst Monitor (GBM) captures lower energies from 8 keV to 40 MeV, together providing comprehensive coverage of the gamma-ray sky. What makes Fermi particularly powerful is its scanning observation strategy: the spacecraft continuously rocks north and south on alternate orbits while moving around Earth, allowing the LAT's wide field of view to survey the entire sky every three hours. This rapid, repetitive scanning enables Fermi to monitor the gamma-ray universe in near real-time, catching transient events like gamma-ray bursts within seconds and tracking variability in sources like blazars over hours to years. This combination of broad energy coverage and rapid all-sky surveying has made Fermi an unparalleled tool for discovering unexpected phenomena and studying the dynamic, high-energy universe.

The discovery potential of Fermi remains high from gamma-ray only observations of the dynamic high-energy sky. In addition, synergies with many multiwavelength and multimessenger observatories that are either new, recently upgraded, or under construction are opening new science opportunities. They will enable advances in understanding the origins and emission processes of gamma-ray bursts (GRBs), the formation and evolution of black holes, the cosmic impacts of the end states of stellar evolution, and the expanding field of gamma-ray cosmology.

Explore more about Fermi science for both technical and non-technical audiences.

Resource	Description
Research Highlights	Highlights specific science results from Fermi.
Publications	Resources for finding Fermi science-related publications
Multimessager Science	Fermi's multimessager and time domain science resources
Our High Energy Universe	E-book with an informal history of the mission and science highlights for a non-technical audience
NASA Science	Official Fermi mission page at NASA Science
NASA Scientific Visualization Studio	Video, images and other media supporting Fermi news products

The Fermi mission enables community science activites, collaboration, and professional development that extends across international boundaries and career stages. Through structured programs including the Guest Investigator program, annual summer schools, science symposia, and mentorship initiatives, Fermi has trained hundreds of early career scientists and supported research at over 150 institutions worldwide. The mission's commitment to rotating leadership roles, facilitating global collaboration, and maintaining open communication channels with the broader scientific community through the Fermi Users' Group ensures sustained productivity and the development of future leaders in gamma-ray astronomy. These collaborative efforts have resulted in over 450 completed Ph.D. theses utilizing Fermi data and continue to support an active and growing international research community.

Guest Investigator Program

The FSSC administers the Guest Investigator (GI) program, which funds the direct analysis of Fermi data, supporting observations in other wavebands, theoretical studies of Fermi sources and projects that produce data products and/or software tools that benefit the Fermi community. GI funds typically support students and postdocs who are working on Fermi science and provide a vital resource for training future generations of researchers.

The GI program is highly productive and supports a wide range of science. Recent highlights include a catalog of approximately 7,400 radio sources associated with unidentified Fermi sources, papers on AGN and blazars, solar flares and cosmology. In addition, the GI program has supported theoretical work on shock models of classical novae, models of pulsar magnetospheres and the discovery of a dipole in the diffuse gamma-ray background that appears to coincide with a similar structure in Ultra High Energy Cosmic Rays discovered by the Pierre Auger observatory.

Community Feedback and Engagement

The Mission meets regularly with a panel of community advisors, the Fermi Users' Group (FUG) , to share updates and receive feedback. The FUG is drawn from relevant science communities and members are external to the project. They serve as the primary interface between the user community and Project in preparation for Senior Reviews. FUG meetings are a forum for the Guest Investigator community to provide feedback to the Project Science team, the FSSC and the instrument teams on mission plans, the GI Program, and science team activities with respect to the planning and execution of Fermi operations.

Fermi science symposia are held every 1-2 years to bring together the broader scientific community and share the latest results and discoveries from the mission.

LAT Collaboration

The LAT Collaboration is a widely distributed international group representing a range of cultures and time zones. The collaboration strives to maintain an environment that can sustain collaborative efforts over many years. The group has identified the availability of regular meetings at times accessible to many time zones as important for bringing the full group together, facilitating transfer of knowledge from older to newer members, and for providing visibility and networking opportunities for newer members. Coordinators across the science working groups use multiple paths for online communication, working together to coordinate weekly virtual group meetings and semi-annual collaboration meetings, one hybrid and one fully virtual, to facilitate interaction. Each collaboration meeting includes a dedicated session for early career members with the LAT PI, administrative lead, and analysis coordinators, to enhance a sense of belonging.

Education and Training Programs

The annual Fermi Summer School in Lewes, Delaware offers lectures on Fermi science and hands-on experiences with Fermi data for graduate students and postdocs. The program has educated hundreds of students about gamma-ray astronomy, Fermi science, and data analysis, with instructors drawn from the FSSC, instrument teams, and user community. Many participants in these graduate-level programs have gone on to careers in the field, using this training to contribute directly to Fermi science and gain experience with a space mission.

Leadership Development and Training

Both Fermi instrument teams provide scientific training through their science working groups, with leadership offering opportunities for scientists to gain experience in managing research and publication efforts. The Collaboration practices teaming junior and senior members as coordinators of working groups, with regular rotations of group leadership to broaden leadership experience and foster teamwork. The LAT team, which has 8 working groups, rotates group leadership typically with 1-2 year cadence. Early career scientists, including postdocs, are regularly offered these roles, giving them leadership experience. This system has trained a cohort of scientists who have advanced from student to faculty and permanent staff positions and continue to lead scientific activities within the collaboration. Task roles within the Fermi have also rotated from senior to junior personnel over the course of the mission, demonstrated by successful transitions of leadership roles for GBM, LAT (science coordinators), ISOC, MOC, FSSC, and Project Science.

The LAT Collaboration provides training and service opportunities for members as Burst Advocates (BAs), Flare Advocates (FAs) and Data Quality Monitoring (DQM) shifters. BAs and FAs respond to astronomical transients by issuing GCN Circulars and ATels. DQM shifters review data, instrument telemetry and pipeline processing so that archived data can be promptly evaluated. These roles are essential to the function of the collaboration and largely supported by early-career members.

The GBM Team's Burst Advocate Program plays a central role in developing new members. BAs gain experience in analysis and have the opportunity to lead major papers about GRB discoveries and serendipitous events, to lead or participate in joint GRB/GW papers and catalog papers, to join team brainstorming, proposals, and papers, and to give invited talks at conferences. For more than a decade, GBM has routinely invited early career scientists to lead high-impact team papers. Expanding the pool of BAs both provides training to early career researchers from a variety of backgrounds and builds connections with other instrument teams.