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  • LAT
  • GBM
  • The Gamma-Ray Large Area Telescope(GLAST) mission is a high-energy gamma-ray observatory designed for making observations in the energy band extending from 20 MeV to 300 GeV with complementary coverage between 8 keV and 30 MeV for γ-ray bursts. ……..
key characteristics

MASS :The GLAST observatory weighs ~4,303 kg

LAT mass : ~2,789 kg

GBM mass :~99.2 kg

DIMENSION of the spacecraft : 2.8 m(high) X 2.5 m in diameter when stowed

POWER CONSUMPTION :~1,500 watts average over an orbit(solar panels supply up to 3,122 watts in sunlight)

DATA DOWNLINK : 40 Mbit/s, multiple contacts per day

LAUNCH SITE : Cape Canaveral Air Station,Flo.

EXPENDABLE LAUNCH VEHICLE : DeltaII Heavy launch vehicle ,with 9 solid rocket boosters.

LAUNCH DATE : early 2008

main mission objectives
  • To understand the mechanism of particle acceleration in AGNs,neutron stars and SNRs
  • Resolve the gamma-ray sky:characterize unidentified sources and diffuse emission,
  • Determine the high-energy behavior of GRBs and variable sources,
  • Probe dark matter and the early universe.

Fig1 : Instruments of GLAST

the large area telescope lat

Fig1: The subsystems of LAT.4x4 modular array.

The LAT has 4 subsystems that work together to detect gamma-rays and reject signals from the intense bombardment of cosmic rays.
  • Tracker
  • Calorimeter
  • Data acquisition system
  • Anticoincidence detector

With its very large FOV,the LAT sees about 20% of the sky at any given moment. It was assembled at SLAC.


Consists of a four-by-four array of tower modules. Each tower module consists of interleaved silicon-strip detectors and lead converter sheets.

SSD are able to more precisely track the electron or positron produced from the initial gamma-ray than previous type of detectors.

SSDs have the ability to determine to location of an object in the sky to within 0.5 to 0.5 arcmin.

The pair conversion signature is also used to help reject the much larger background of charged cosmic rays.

Fig3 : The LAT has 16 towers of particle detectors

In each module, there are 19 pairs of planes of silicon-in each pair,one plane has the strips ,oriented in the X-direction , while other has the strips oriented in the perpendicular Y-direction.

When a particle interacts in the silicon ,its position on the plane can therefore be determined in two dimensions.

The third dimension of the track is determined by analyzing signals from adjacent planes, as the particle travels down through the telescope towards the calorimeter.

Fig4 : A cross-section of the TRACKER.

lat specifications and performance compared with egret
LAT Specifications and Performance Compared with EGRET

1 After background rejection2 Single photon, 68% containment, on-axis3 1-σ, on-axis4 1-σ radius, flux 10-7 cm-2 s-1 (>100 MeV), high|b|5> 100 MeV, at high |b|, for exposure of one-year all sky survey, photon spectral index -2


The calorimeter design for GLAST produces flashes of light that are used to determine how much energy is in each γ-ray.

CsI(Tl) bars, arranged in a segmented manner, give both longitudinal and transverse information about the energy deposition pattern.

Cesium-iodide blocks are arranged in two perpendicular directions, to provide additional positional information about the shower.

Fig5 : CsI bars..


The data acquisition system (DAQ) is the brain behind GLAST, as it makes the initial distinction between false signals and real gamma ray signals, and decides which of the signals should be relayed to the ground.

The DAQ consists of specialized electronics and 32-bit radiation-hard processors that record and analyze the information generated by the silicon-strip detectors and the calorimeter.


The ACD is LAT’S first-level defense against the charged vosmic ray background that outnumbers the γ-rays by 3-5 orders of magnitude.

The ACD covers the top and 4 sides of the LAT tracking detector,requiring a total active area of ~8.3 m2 .

It uses the plastic scintillator tiles with wavelength shifting fiber readout.

Fig6 : ACD in final phase of integration. The bottom tile rows are not installed yet.

the glast burst monitor gbm
  • The GLAST Burst Monitor (GBM) was selected as a complementary instrument for the GLAST mission and will be sensitive to X-rays and gamma rays with energies between 8 keV and 30 MeV.
  • The combination of the GBM and the LAT provides a powerful tool for studying gamma-ray bursts, particularly for time-resolved spectral studies over a very large energy band.
The development of the GLAST Burst Monitor and analysis of its observational data is a collaborative effort between the National Space Science and Technology Center in the U.S. and the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany. The Principal Investigator is Dr. Charles Meegan at MSFC. Dr. Giselher Lichti at MPE is co-PI.

Fig7: GLAST Burst Monitor Principal Investigator Charles Meegan,an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville,tests the GBM.

The primary objective of the GBM is to augment the GLAST LAT scientific return from GRBs.This will be achieved by:
  • extending the energy range of burst spectra down to 5 keV.
  • providing real time burst locations over a wide field-of-view (FOV) with sufficient accuracy to repoint the GLAST spacecraft.
  • in addition to supplementing or initiating LAT GRB observations, the GBM scientific program will include:

--the generation and dissemination of near real-time burst locations accurate enough to initiate counterpart searches by ground or space-based observers.

slide20 untriggered burst search in the GBM data to extend the detection threshold to an estimated 0.35 ph/cm2/s.

5. production and publication of a catalog of GRBs detected by the GBM including those uncovered in the search for untriggered events. This catalog will contain parameters such as burst fluence, peak flux, and duration.

6. the availability of archived data for investigations into non-GRB phenomena such as solar flares, galactic black-hole candidates, and soft gamma-ray repeaters (SGR), which may be strong and variable above background radiation levels in the hard X-ray regime.

The GLAST Burst Monitor includes 12 Sodium Iodide (NaI)scintillation detectors and 2 Bismuth Germanate (BGO)scintillation detectors.
  • The NaI detectors cover the lower part of the energy range, from a few keV to about 1 MeV and provide burst triggers and locations.
  • The BGO detectors cover the energy range of 150 keV -30 MeV, providing a good overlap with the NaI at the lower end, and with the LAT at the high end.
  • Together the NaI and BGO detectors have similar characteristics to the combination of the BATSE large area and spectroscopy detectors but cover a wider energy range and have a smaller collection area.

Fig8 : (UP)NaI detector-shipped from Jena Optronik August 2002.

(DOWN)Engineering Quality model BGO Detector on test bench at NSSTC June 2005

the differences between swift glast
The Differences Between SWIFT & GLAST
  • Both missions look at GRBs, but in different ways:

SWIFT can rapidly and precisely determine the location the GRBs and observe their afterglows at X-ray,ultraviolet and optical wavelengths.

  • GLAST will provide exquisite observations of the burst over the gamma-ray spectrum. Beyond GRB science, GLAST is a multipurpose observatory that will study a broad range of cosmic phenomena. SWIFT is also a multipurpose observatory ,but was built primarily to study GRBs.
  • GLAST science writer’s guide,NASA 2007

  • NASA’s Goddard Space Flight Center

3. Sonoma State University

  • U.S. National Research Lab.