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OUTLINE OUTLINE

• OVERVIEWOVERVIEW

• MAIN MISSION OBJECTIVESMAIN MISSION OBJECTIVES

• INSTRUMENTSINSTRUMENTS

1.1. LATLAT

2.2. GBMGBM

• AGILE-EGRET-GLAST COMPARISIONAGILE-EGRET-GLAST COMPARISION

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OVERVIEWOVERVIEW

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

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KEY CHARACTERISTICSKEY 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

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MAIN MISSION OBJECTIVESMAIN MISSION OBJECTIVES

To understand the mechanism of particle To understand the mechanism of particle acceleration in AGNs,neutron stars and SNRsacceleration in AGNs,neutron stars and SNRs

Resolve the gamma-ray sky:characterize Resolve the gamma-ray sky:characterize unidentified sources and diffuse emission,unidentified sources and diffuse emission,

Determine the high-energy behavior of GRBs and Determine the high-energy behavior of GRBs and variable sources,variable sources,

Probe dark matter and the early universe.Probe dark matter and the early universe.

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INSTRUMENTSINSTRUMENTS

Fig1 : Instruments of GLAST

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THE LARGE AREA TELESCOPETHE LARGE AREA TELESCOPELATLAT

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

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The LAT has 4 subsystems that work together to The LAT has 4 subsystems that work together to detect gamma-rays and reject signals from the detect gamma-rays and reject signals from the intense bombardment of cosmic rays.intense bombardment of cosmic rays.

1.1. Tracker Tracker

2.2. CalorimeterCalorimeter

3.3. Data acquisition systemData acquisition system

4.4. Anticoincidence detectorAnticoincidence detector

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

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

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

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

The pair conversion signature is also The pair conversion signature is also used to help reject the much larger used to help reject the much larger background of charged cosmic rays.background of charged cosmic rays. Fig3 : The LAT has 16 towers of

particle detectors

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

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

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

Fig4 : A cross-section of the TRACKER.Fig4 : A cross-section of the TRACKER.

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LAT Specifications and Performance Compared LAT Specifications and Performance Compared with EGRETwith EGRET

QUANTITYQUANTITY LAT(Min.SpecLAT(Min.Spec.).)

EGRETEGRET

Energy range 20 MeV-300 GeV 20 MeV-30 GeV

Peak effective area 1

›8000 cm2 1500 cm2

FOV ›2 sr 0.5 sr

Angular resolution 2 ‹ 3.5˚(100 MeV)‹ 0.15˚(›10 GeV)

5.8˚(100 MeV)

Energy resolution 3 ‹ 10 % 10 %

Dead time per event

‹ 100 μs 100 ms

Source location 4

determination ‹ 0.5’ 15’

Point source 5

sensitivity‹ 6x10-9 cm-2 s -1 ~ 10-7 cm-2 s -1

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

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2. CALORIMETER ;

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

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

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

Fig5 : CsI bars..

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3. DATA ACQUISITION SYSTEM ;(DAQ)

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

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

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4. 4. ANTICOINCIDENCE ANTICOINCIDENCE DETECTOR DETECTOR ;;

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.

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THE GLAST BURST MONITORTHE GLAST BURST MONITORGBMGBM

The GLAST Burst Monitor (GBM) was selected as a The GLAST Burst Monitor (GBM) was selected as a complementary instrument for the GLAST mission complementary instrument for the GLAST mission and will be sensitive to X-rays and gamma rays and will be sensitive to X-rays and gamma rays with energies between with energies between 8 keV and 30 MeV8 keV and 30 MeV. .

The combination of the GBM and the LAT provides The combination of the GBM and the LAT provides a powerful tool for studying gamma-ray bursts, a powerful tool for studying gamma-ray bursts, particularly for time-resolved spectral studies particularly for time-resolved spectral studies over a very large energy band.over a very large energy band.

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The development of the The development of the GLAST Burst Monitor and GLAST Burst Monitor and analysis of its analysis of its observational data is a observational data is a collaborative effort collaborative effort between the National between the National Space Science and Space Science and Technology Center in the Technology Center in the U.S. and the Max Planck U.S. and the Max Planck Institute for Extraterrestrial Institute for Extraterrestrial Physics (MPE) in Germany. Physics (MPE) in Germany. The Principal Investigator The Principal Investigator is Dr. Charles Meegan at is Dr. Charles Meegan at MSFC. Dr. Giselher Lichti at MSFC. Dr. Giselher Lichti at

MPE is co-PIMPE 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.

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The primary objective of the GBM is to augment the GLAST The primary objective of the GBM is to augment the GLAST LAT scientific return from GRBs.This will be achieved by: LAT scientific return from GRBs.This will be achieved by:

1.1. extending the energy range of extending the energy range of burst spectraburst spectra down to 5 down to 5 keV. keV.

2.2. providing real time burst locations over a wide field-of-providing real time burst locations over a wide field-of-view (FOV) with sufficient accuracy to repoint the GLAST view (FOV) with sufficient accuracy to repoint the GLAST spacecraft. spacecraft.

3.3. in addition to supplementing or initiating LAT GRB in addition to supplementing or initiating LAT GRB observations, the GBM scientific program will include: observations, the GBM scientific program will include:

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

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

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

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

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The GLAST Burst Monitor The GLAST Burst Monitor includes 12 Sodium Iodide (NaI)includes 12 Sodium Iodide (NaI) scintillation detectors and 2 scintillation detectors and 2 Bismuth Germanate Bismuth Germanate (BGO)scintillation detectors. (BGO)scintillation detectors.

The NaI detectors cover the The NaI detectors cover the lower part of the energy range, lower part of the energy range, from a few keV to about 1 MeV from a few keV to about 1 MeV and provide burst triggers and and provide burst triggers and locations. locations.

The BGO detectors cover the The BGO detectors cover the energy range of 150 keV -30 energy range of 150 keV -30 MeV, providing a good overlap MeV, providing a good overlap with the NaI at the lower end, with the NaI at the lower end, and with the LAT at the high end. and with the LAT at the high end.

Together the NaI and BGO Together the NaI and BGO detectors have similar detectors have similar characteristics to the characteristics to the combination of the BATSE large combination of the BATSE large area and spectroscopy detectors area and spectroscopy detectors but cover a wider energy range but cover a wider energy range and have a smaller collection and have a smaller collection area.area.

Fig8 : (UP)NaI detector-shipped from Jena Optronik August 2002.(DOWN)Engineering Quality model BGO Detector on test bench at NSSTC June 2005

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Fig9 : NaI and BGO detectors in thermal vacuum chamber at MPE ,April 2005.

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BATSE & GBM CHARACTERISTICSBATSE & GBM CHARACTERISTICS

CHARACTERISTIC BATSE GBMTotal Mass 850 kg 115 kg

Trigger Threshold ~0.2 ph/cm2/s 0.61 ph/cm2/s(true thrs.)

Telemetry Rate 3.55 kbps 15-25 kbps

LARGE AREA DETECTORS LOW_ENERGY DETECTORS

Material NaI NaI

Number 8 12

Area 2025 cm2 126 cm2

Thickness 1.27 cm 1.27 cm

Energy Range 25 keV- 1.8 MeV 8 keV – 1 MeV

SPECTROSCOPY DETECTORS

HIGH-ENERGY DETECTORS

Material NaI BGO

Number 8 2

Area 126 cm2 126 cm2

Thickness 7.62 cm 12.7 cm

Energy Range 30 keV – 10 MeV 150 keV -30 MeV

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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.

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REFERENCES:

1. GLAST science writer’s guide,NASA 2007

http://www.nasa.gov/glast/

2. NASA’s Goddard Space Flight Center

http://glast.gsfc.nasa.gov/

3. Sonoma State University

http://glast.sonoma.edu/

4. U.S. National Research Lab.

http://heseweb.nrl.navy.mil/glast/index.html/

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THE END