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Fermi Gamma-ray Space Telescope

                   
Fermi Gamma-ray Space Telescope
GLAST on the payload attach fitting.jpg
Fermi on Earth, solar arrays folded
General information
NSSDC ID 2008-029A
Organization NASA, United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.
Major contractors General Dynamics
Launch date 2008-06-11 16:05 UTC
Launched from Space Launch Complex 17-B Cape Canaveral Air Force Station
Launch vehicle Delta II 7920-H
Mission length elapsed: 4 years and 12 days
Orbit height 550 km (340 mi)
Orbit period ~ 95 minutes
Wavelength gamma ray
Instruments
LAT Large Area Telescope
GBM Gamma-ray Burst Monitor
Website fermi.gsfc.nasa.gov/

The Fermi Gamma-ray Space Telescope , formerly referred to as the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts.[1]

Fermi was launched on 11 June 2008 at 16:05 GMT aboard a Delta II 7920-H rocket. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.[2]

Contents

  Overview

Fermi includes two scientific instruments, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The LAT is an imaging gamma-ray detector (a pair-conversion instrument) which detects photons with energy from about 30 million to about 300 billion electron volts (30 MeV to 300 GeV), with a field of view of about 20% of the sky; it may be thought of as a sequel to the EGRET instrument on the Compton gamma ray observatory. The GBM consists of 14 scintillation detectors (twelve sodium iodide crystals for the 8 keV to 1 MeV range and two bismuth germanate crystals with sensitivity from 150 keV to 30 MeV), and can detect gamma-ray bursts in that energy range across the whole of the sky not occluded by the Earth.

General Dynamics Advanced Information Systems (formerly Spectrum Astro and now Orbital Sciences) in Gilbert, Arizona designed and built the spacecraft that carries the instruments. It travels in a low, circular orbit with a period of about 95 minutes. Its normal mode of operation maintains its orientation so that the instruments will look away from the earth, with a “rocking” motion to equalize the coverage of the sky. The view of the instruments will sweep out across most of the sky about 16 times per day. The spacecraft can also maintain an orientation that points to a chosen target.

Both science instruments underwent environmental testing, including vibration, vacuum, and high and low temperatures to ensure that they can withstand the stresses of launch and continue to operate in space. They were integrated with the spacecraft at the General Dynamics ASCENT facility in Gilbert, Arizona.

Data from the instruments are available to the public through the Fermi Science Support Center web site. Software for analyzing the data is also available.

  Fermi G.S.T. logo
What is Fermi.ogv
 
  What is Fermi?
  Artist's conception of Fermi in orbit

  GLAST renamed Fermi Gamma-ray Space Telescope

Fermi gained its new name in 2008: On 26 Aug 2008, GLAST was renamed the “Fermi Gamma-ray Space Telescope” in honor of Enrico Fermi, a pioneer in high-energy physics.[3]

NASA’s Alan Stern, associate administrator for Science at NASA Headquarters, launched a public competition 7 Feb 2008, closing 31 Mar 2008, to rename GLAST in a way that would “capture the excitement of GLAST’s mission and call attention to gamma-ray and high-energy astronomy... something memorable to commemorate this spectacular new astronomy mission... a name that is catchy, easy to say and will help make the satellite and its mission a topic of dinner table and classroom discussion”.[4][5]

  Mission

  Anticipated operations timeline.
  The GLAST instrument after arriving at Cape Canaveral in May 2008

NASA designed the mission with a five-year lifetime, with a goal of ten years of operations.[6]

The key scientific objectives of the Fermi mission have been described as:[7]

  • To understand the mechanisms of particle acceleration in active galactic nuclei (AGN), pulsars, and supernova remnants (SNR).
  • Resolve the gamma-ray sky: unidentified sources and diffuse emission.
  • Determine the high-energy behavior of gamma-ray bursts and transients.
  • Probe dark matter (e.g. by looking for an excess of gamma rays from the center of the Milky Way) and early Universe.
  • Search for evaporating primordial micro black holes (MBH) from their presumed gamma burst signatures [Hawking Radiation component].

The National Academies of Sciences ranked this mission as a top priority.[8] Many new possibilities and discoveries are anticipated to emerge from this single mission and greatly expand our view of the Universe.[8][9] (The following list is abbreviated as discoveries are made. To read about discoveries already made, see "Discoveries" below.)

Study energy spectra and variability of wavelengths of light coming from blazars so as to determine the composition of the black hole jets aimed directly at Earth -- whether they are
(a) a combination of electrons and positrons or
(b) only protons.
Study gamma-ray bursts with an energy range several times more intense than ever before so that scientists may be able to understand them better.
Study younger, more energetic pulsars in the Milky Way than ever before so as to broaden our understanding of stars. Study the pulsed emissions of magnetospheres so as to possibly solve how they are produced. Study how pulsars generate winds of interstellar particles.
Provide new data to help improve upon existing theoretical models of our own galaxy.
Study better than ever before whether ordinary galaxies are responsible for gamma-ray background radiation. The potential for a tremendous discovery awaits if ordinary sources are determined to be irresponsible, in which case the cause may be anything from self-annihilating dark matter to entirely new chain reactions among interstellar particles that have yet to be conceived.
Study better than ever before how concentrations of visible and ultraviolet light change over time. The mission should easily detect regions of spacetime where gamma-rays interacted with visible or UV light to make matter. This can be seen as an example of E=mc2 working in reverse, where energy is converted into mass, in the early universe.
Study better than ever before how our own Sun produces gamma rays in solar flares.
Search for evidence that dark matter is made up of weakly interacting massive particles, complementing similar experiments already planned for the Large Hadron Collider as well as other underground detectors. The potential for a tremendous discovery in this area is possible over the next several years.
Test better than ever before certain established theories of physics, such as whether the speed of light in vacuum remains constant regardless of wavelength. Einstein's general theory of relativity contends that it does, yet some models in quantum mechanics and quantum gravity predict that it may not. Search for gamma rays emanating from former black holes that once exploded, providing yet another potential step toward the unification of quantum mechanics and general relativity. Determine whether photons naturally split into smaller photons, as predicted by quantum mechanics and already achieved under controlled, man-made experimental conditions.
  • Unknown discoveries[19]
Scientists estimate a very high possibility for new scientific discoveries, even revolutionary discoveries, emerging from this single mission.

  Mission status

  Prelaunch

  GLAST launch aboard a Delta II rocket, 11 June 2008.
  GLAST launch as pictured by a space-based infrared sensor, looking down at the Earth.

On 4 Mar 2008 the spacecraft arrived at the Astrotech payload processing facility in Titusville, Florida.[20] On 4 Jun 2008, after several previous delays, launch status was retargeted for June 11 at the earliest,[21][22] the last delays resulting from the need to replace the Flight Termination System batteries.[23] The launch window extended from 11:45 a.m. until 1:40 p.m. EDT (15:45-17:40 GMT) daily, until 7 Aug 2008.[23]

  Launch

Launch occurred successfully on 11 Jun 2008 at 16:05, and the spacecraft separated from the carrier rocket about 75 minutes later. The spacecraft departed from pad B at Cape Canaveral Air Force Station Space Launch Complex 17 aboard a Delta 7920H-10C rocket.

  Orbit

Fermi resides in a low-earth circular orbit at an altitude of 550 km (340 mi), and at an inclination of 28.5 degrees.[24]

  Software modifications

GLAST received some minor modifications to its computer software 2008-06-23.

  LAT/GBM computers operational

Computers operating both the LAT and GBM and most of the LAT’s components were turned on, 2008-06-24. The LAT high voltage was turned on, 2008-06-25, and it began detecting high-energy particles from space, but minor adjustments were still needed to calibrate the instrument. The GBM high voltage was also turned on, 2008-06-25, but the GBM still required one more week of testing/calibrations before searching for gamma-ray bursts.

  Sky survey mode

After presenting an overview of the Fermi instrumentation and goals, Jennifer Carson of SLAC National Accelerator Laboratory had concluded that the primary goals were “all achievable with the all-sky scanning mode of observing”.[25] Fermi switched to "sky survey mode" on 26 June 2008 so as to begin sweeping its field of view over the entire sky every three hours (every two orbits).

  Discoveries

  Cycle of pulsed gamma rays from the Vela pulsar. Constructed from photons detected by Fermi's Large Area Telescope.

  Pulsar discovery

The first major discovery came when the space telescope detected a pulsar in the CTA 1 supernova remnant that appeared to emit radiation in the gamma ray bands only, a first for its kind.[26] This new pulsar sweeps the earth every 316.86 milliseconds and is about 4,600 light years away.[27]

  Greatest GRB energy release

In September 2008, the gamma-ray burst GRB 080916C in the constellation Carina was recorded by the Fermi telescope. This burst is notable as having “the largest apparent energy release yet measured”.[28] The explosion had the power of about 9,000 ordinary supernovae, and the relativistic jet of material ejected in the blast must have moved at a minimum of 99.9999% the speed of light. Overall, GRB 080916C had “the greatest total energy, the fastest motions, and the highest-energy initial emissions” ever seen.[29]

  Cosmic rays and supernova remnants

In February 2010,[30] it was announced that Fermi-LAT had determined that supernova remnants act as enormous accelerators for cosmic particles. This determination fulfills one of the stated missions for this project.[31]

  Background gamma ray sources

In March 2010 it was announced that active galactic nuclei are not responsible for most gamma-ray background radiation.[32] Though active galactic nuclei do produce some of the gamma-ray radiation detected here on Earth, less than 30% originates from these sources. The search now is to locate the sources for the remaining 70% or so of all gamma-rays detected. Possibilities include star forming galaxies, galactic mergers, and yet-to-be explained dark matter interactions.

  Milky Way Gamma/X-ray bubbles

In November 2010, it was announced two gamma-ray & x-ray bubbles were detected around Earth’s galaxy, the Milky Way.[33] The bubbles extend about 25 thousand light years distant above and below the center of the galaxy.[33] The galaxy's diffuse gamma-ray fog hampered prior observations, but the discovery team led by D. Finkbeiner, building on research by G. Dobler, worked around this problem.[33]

  X-ray/gamma-ray bubbles of Earth’s Galaxy, the Milky Way. (Art)
Gamma-ray Bubbles.ogv
  Using data from NASA's Fermi Gamma-ray Space Telescope, scientists have discovered a gigantic, mysterious structure in our galaxy. This never-before-seen feature looks like a pair of bubbles extending above and below our galaxy's center.

  Highest energy light ever seen from the Sun

In early 2012, Fermi/GLAST observed the highest energy light ever seen in a solar eruption.[34]

At the flare's peak, the LAT detected gamma rays with two billion times the energy of visible light, or about four billion electron volts (GeV), easily setting a record for the highest-energy light ever detected during or immediately after a solar flare
—NASA[34]

Particles were accelerated to 2/3 the speed of light in three seconds.[34]

  Fermi science packages

  Gamma-ray Burst Monitor (GBM)

The Gamma-ray Burst Monitor (GBM) (formerly GLAST Burst Monitor) detects sudden flares of gamma-rays produced by gamma ray bursts and solar flares. Its scintillators are on the sides of the spacecraft to view all of the sky which is not blocked by the earth. The design is optimized for good resolution in time and photon energy.

"Gamma-ray bursts are so bright we can see them from billions of light years away, which means they occurred billions of years ago, and we see them as they looked then," stated Charles Meegan of NASA's Marshall Space Flight Center.[35]

The Gamma-ray Burst Monitor has detected gamma rays from positrons generated in powerful thunderstorms.[36]

  GBM participating institutions

  US team institution
  German team institutions

  Large Area Telescope (LAT)

The Large Area Telescope (LAT) detects individual gamma rays using technology similar to that used in terrestrial particle accelerators. Photons hit thin metal sheets, converting to electron-positron pairs, via a process known as pair production. These charged particles pass through interleaved layers of silicon microstrip detectors, causing ionization which produce detectable tiny pulses of electric charge. Researchers can combine information from several layers of this tracker to determine the path of the particles. After passing through the tracker, the particles enter the calorimeter, which consists of a stack of caesium iodide scintillator crystals to measure the total energy of the particles. The LAT's field of view is large, about 20% of the sky. The resolution of its images is modest by astronomical standards, a few arc minutes for the highest-energy photons and about 3 degrees at 100 MeV. The LAT is a bigger and better successor to the EGRET instrument on NASA's Compton Gamma Ray Observatory satellite in the 1990s. Several countries produced the components of the LAT, who then sent the components for assembly at SLAC National Accelerator Laboratory.

  LAT participating institutions

  US team institutions
  Austrian team institution
  German team institutions
  Japanese team institutions
  Icelandic team institutions
  Italian team institutions
  French team institutions
  Spanish team institution
  Swedish team institutions

  Education and public outreach

Education and public outreach are important components of the Fermi project. The main Fermi education and public outreach website at http://glast.sonoma.edu offers gateways to resources for students, educators, scientists, and the public. NASA’s Education and Public Outreach (E/PO) group operates the Fermi education and outreach resources at Sonoma State University.

  Rossi Prize

The 2011 Bruno Rossi Prize was awarded to Bill Atwood, Peter Michelson and the Fermi LAT team "for enabling, through the development of the Large Area Telescope, new insights into neutron stars, supernova remnants, cosmic rays, binary systems, active galactic nuclei and gamma-ray bursts."[37]

  Discoveries

Fermi Discovers Youngest Millisecond Pulsar.ogv
  Fermi discovers youngest millisecond pulsar.
  Gamma-ray pulsars detected by the Fermi Gamma-ray Space Telescope.

  References

  1. ^ "NASA's GLAST Burst Monitor Team Hard at Work Fine-Tuning Instrument and Operations". NASA. 2008-07-28. http://www.nasa.gov/mission_pages/GLAST/news/glast_gbm.html. 
  2. ^ "An Astro-Particle Physics Partnership Exploring the High Energy Universe - List of funders". SLAC. http://www-glast.stanford.edu/. Retrieved August 9, 2007. 
  3. ^ "First Light for the Fermi Space Telescope". NASA. 2008-08-26. http://science.nasa.gov/headlines/y2008/26aug_firstlight.htm. 
  4. ^ "NASA Calls for Suggestions to Re-Name Future Telescope Mission". NASA. 2008-02-07. http://www.nasa.gov/home/hqnews/2008/feb/HQ_08036_GLAST.html. Retrieved 2008-02-10. 
  5. ^ "Name that Space Telescope!". NASA. 2008-02-08. http://science.nasa.gov/headlines/y2008/08feb_namethattelescope.htm. 
  6. ^ "The GLAST Mission: GLAST Overview, mission length". NASA. http://glast.gsfc.nasa.gov/public/. Retrieved August 9, 2007. 
  7. ^ "The Mission". SLAC. http://www-glast.stanford.edu/mission.html. Retrieved August 9, 2007. 
  8. ^ a b "NASA - Q&A ON THE GLAST MISSION". Nasa: Fermi Gamma-ray Space Telescope. NASA. 28 August 2008. http://www.nasa.gov/mission_pages/GLAST/main/questions_answers.html. Retrieved 29 April 2009. 
  9. ^ See also Nasa - Fermi Science and NASA - Scientists Predict Major Discoveries for GLAST.
  10. ^ NASA - Blazars and Active Galaxies. Nasa.gov (2008-08-28). Retrieved on 2010-11-16.
  11. ^ NASA - GLAST Gamma-ray Bursts. Nasa.gov (2008-08-28). Retrieved on 2010-11-16.
  12. ^ NASA - Neutron Stars. Nasa.gov. Retrieved on 2010-11-16.
  13. ^ NASA - Milky Way Galaxy. Nasa.gov (2008-08-28). Retrieved on 2010-11-16.
  14. ^ NASA - The Gamma-ray Background. Nasa.gov (2008-08-28). Retrieved on 2010-11-16.
  15. ^ NASA - The Early Universe. Nasa.gov (2008-08-28). Retrieved on 2010-11-16.
  16. ^ NASA - Solar System: Sun, Moon, and Earth. Nasa.gov. Retrieved on 2011-09-02.
  17. ^ NASA - Dark Matter. Nasa.gov (2008-08-28). Retrieved on 2010-11-16.
  18. ^ NASA - Testing Fundamental Physics. Nasa.gov (2008-08-28). Retrieved on 2010-11-16.
  19. ^ NASA - Scientists Predict Major Discoveries for GLAST. Nasa.gov (2008-08-28). Retrieved on 2010-11-16.
  20. ^ "GLAST Spacecraft Arrives in Florida to Prepare for Launch". NASA. http://www.nasa.gov/centers/kennedy/news/releases/2008/release-20080304.html. 
  21. ^ "Spaceflight Now – Tracking Station — Worldwide launch schedule". http://www.spaceflightnow.com/tracking/index.html. Retrieved 2008-06-04. 
  22. ^ "GLAST Mission: Coverage Latest News". http://www.nasa.gov/mission_pages/GLAST/main/index.html. Retrieved 2008-06-04. 
  23. ^ a b "NASA - Expendable Launch Vehicle Status Report". NASA. 2008-06-06. http://www.nasa.gov/centers/kennedy/launchingrockets/status/2008/elvstatus-20080606.html. Retrieved 2008-06-09. 
  24. ^ "The GLAST Mission: GLAST Overview, orbital information". NASA. http://glast.gsfc.nasa.gov/public/. Retrieved August 9, 2007. 
  25. ^ Carson, Jennifer (2007). "GLAST: physics goals and instrument status". Journal of Physics: Conference Series 60: 115–118. arXiv:astro-ph/0610960. Bibcode 2007JPhCS..60..115C. DOI:10.1088/1742-6596/60/1/020. 
  26. ^ Fermi Telescope Makes First Big Discovery: Gamma Ray Pulsar. Universe Today. Retrieved on 2010-11-16.
  27. ^ Cosmos Online - New kind of pulsar discovered
  28. ^ The Fermi LAT and Fermi GBM Collaborations (2009). "Fermi Observations of High-Energy Gamma-Ray Emission from GRB 080916C". Science 323 (922): 1688–1693. Bibcode 2009Sci...323.1688A. DOI:10.1126/science.1169101. PMID 19228997. 
  29. ^ "Most Extreme Gamma-ray Blast Ever, Seen By Fermi Gamma-ray Telescope". Science Daily. February 19, 2009. http://www.sciencedaily.com/releases/2009/02/090219141458.htm. Retrieved January 13, 2010. 
  30. ^ NASA’s Fermi Closes on Source of Cosmic Rays, NASA
  31. ^ Cosmic Rays and Supernova Remnants, NASA
  32. ^ NASA’s Fermi Probes “Dragons” of the Gamma-ray Sky, NASA
  33. ^ a b c Astronomers find giant, previously unseen structure in our galaxy (November 9, 2010) - E! Science News
  34. ^ a b c NASA's Fermi Detects the Highest-Energy Light From a Solar Flare 06.11.12
  35. ^ "GLAST Off!". NASA. http://science.nasa.gov/headlines/y2008/11jun_glast2.htm. 
  36. ^ http://www.nasa.gov/mission_pages/GLAST/news/fermi-thunderstorms.html
  37. ^ "Astronomers Honored for Excellence by the American Astronomical Society". http://aas.org/press/pr2011Jan18. 

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