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GLAST:Gamma Ray Large Area Telescope. The GLAST Mission and its Physics reach R.Bellazzini INFN - sez. Pisa. Nature's Highest Energy Particle Accelerators . OUTLINE Introduction Pair-Conversions Telescopes The LAT Design LAT Performance GLAST Science Topics Conclusions .

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GLAST:Gamma Ray Large Area Telescope

The GLAST Mission

and its Physics reach


INFN - sez. Pisa

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Nature's Highest Energy Particle Accelerators



Pair-Conversions Telescopes

The LAT Design

LAT Performance

GLAST Science Topics


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Polarization of cosmic

microwave background

Large scale structure

Profound Connection between Astrophysics & HEP

The fundamental theory ofCosmic Genesis and the questfor experimental evidencehas led to new and potential partnerships between Astrophysics and HEP.

  • Some Areas of Collaboration:

  • Origin of cosmic rays

  • Dark Matter Searches

  • CMBR

  • Quantum gravity

  • Structure Formation

  • Early Universe Physics

  • Understanding the HE Universe

This quest is changing the face of both fields.

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Sources in Third EGRET Catalog

First Came EGRET

Raised many interesting issues andquestions which can be addressed by a NASA mid-class mission (Delta II).

Launched in April 1991

  • Observed over 60 AGN in > 100 MeV gammas.

  • About 1/2 dozen GRB at

  • high energy.

  • Measurement of diffuse

  • gamma ray background to

  • over 10 GeV.

  • One hundred and seventy

  • unidentified sources in 3rd

  • EGRET catalog. Mystery of

  • unidentifieds since 1970s

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0.01 GeV 0.1 GeV 1 GeV 10 GeV 100 GeV 1 TeV








discovery reach

Area (square cm)


0.01 0.1 1 10 100 1000

Energy (GeV)

GLAST Science

Map the High-Energy Universe

Supernova Remnants


  • Physics in regions of strong gravity, huge electric & magnetic fields: e.g. particle production & acceleration near the event horizon of a black hole.

  • Use gamma-rays from AGNs to study evolution of the early universe.

  • Physics of gamma-ray bursts at cosmological distances.

  • Probe the nature of particle dark matter: e.g., wimps, 5-10 eV neutrino.

  • Decay of relics from the Big Bang.

  • GLAST pulsar survey: provide a new window on the galactic neutron star population.

  • “Map” the pulsar magnetosphere and understand the physics of pulsar emission.

  • Origin of cosmic-rays: characterize extended supernovae sources.

  • Determine the origin of the isotropic diffuse gamma-ray background.

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GLAST Concept 10 GeV 100 GeV 1 TeV

Low profile for wide f.o.v.

Segmented anti-shield to minimize self-veto at high E.

Finely segment calorimeter for enhanced background rejection and shower leakage correction.

High-efficiency, precise track detectors located close to the conversions foils to minimize multiple-scattering errors.

Modular, redundant design.

No consumables.

Low power consumption (580 W)

Pair-Conversion Telescope

Charged particle anticoincidence shield

Conversion foils

Particle tracking detectors



  • Calorimeter

  • (energy measurement)

Photons materialize into matter-antimatter pairs:

E -> me+c2 + me-c2

The large area telescope lat l.jpg
The Large Area Telescope (LAT) 10 GeV 100 GeV 1 TeV



Thermal Blanket


DAQ Electronics


  • Array of 16 identical “Tower” Modules, each with a tracker (Si strips) and a calorimeter (CsI with PIN diode readout) and DAQ module.

  • Surrounded by finely segmented ACD (plastic scintillator with PMT readout).

  • Aluminum strong-back “Grid,” with heat pipes for transport of heat to the instrument sides.

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The LAT Hardware 10 GeV 100 GeV 1 TeV

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Tray assembling 10 GeV 100 GeV 1 TeV

  • Trays are C-composite panels (Al hexcel core)

  • Carbon-fiber walls provide stiffness and the thermal

  • pathway from electronics to the grid.

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GLAST Tracker Design Overview 10 GeV 100 GeV 1 TeV

One Tracker Tower Module

Carbon thermal panel

Electronics flex cables

  • 16 “tower” modules, each with 37cm  37cm of active cross section

  • 83m2 of Si in all, like ATLAS

  • 11500 SSD, ~ 1M channels

  • 18 x,y planes per tower

    • 19 “tray” structures

      • 12 with 3% Pb or W on bottom (“Front”)

      • 4 with 18% Pb or W on bottom (“Back”)

      • 2 with no converter foils

    • Every other tray is rotated by 90°, so each Pb foil is followed immediately by an x,y plane of detectors

      • 2mm gap between x and y oriented detectors

  • Trays stack and align at their corners

  • The bottom tray has a flange to mount on the grid.

  • Electronics on sides of trays:

    • Minimize gap between towers

    • 9 readout modules on each of 4 sides

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Prototyping of the GLAST SSD 10 GeV 100 GeV 1 TeV

Preserie HPK detector

on 6’’ wafer

Gained experience with a large number of SSD (~5% of GLAST needs)

Additional Prototypes:

Micron (UK), STM (Italy), CSEM (Switzerland)

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International Collaboration 10 GeV 100 GeV 1 TeV

  • Organizations with LAT Hardware Involvement

    • Stanford University & Stanford Linear Accelerator Center

    • NASA Goddard Space Flight Center

    • Naval Research Laboratory

    • University of California at Santa Cruz

    • University of Washington

    • Commissariat a l’Energie Atomique, Departement d’Astrophysique (CEA)

    • Institut National de Physique Nuclearie et de Physique des Particules (IN2P3):

    • Ecole Polytechnique, College de France, CENBG (Bordeaux)

    • Hiroshima University

    • Institute of Space and Astronautical Science, Tokyo

    • RIKEN

    • Tokyo Institute of Technology

    • Istituto Nazionale di Fisica Nucleare (INFN): Pisa, Trieste, Bari, Udine, Perugia, Roma

    • Royal Institute of Technology (KTH), Stockholm








  • expertise in each science topic (theory + obs.)

  • experience in high-energy and space instrumentation

  • access to X-ray, MeV, and TeV observatories by collaboration

    for multi-wavelength observations

  • ‘mirror’ data site in Europe

~ 100 collaborators

from 28 institutions

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Calendar Years 10 GeV 100 GeV 1 TeV









Inst. Delivery














Build & Test

Flight Units

Build & Test

Engineering Models



Project schedule

SSD Procurement

Ladder Production

Tray Assembly

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LAT Instrument Performance 10 GeV 100 GeV 1 TeV

Including all Background & Track Quality Cuts

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GLAST Science Capability 10 GeV 100 GeV 1 TeV

Key instrument features that enhance GLAST’s science reach:

  • Peak effective area: 12,900 cm2

  • Precision point-spread function (<0.10° for E=10 GeV)

  • Excellent background rejection: better than 2.5105:1

  • Good energy resolution for all photons (<10%)

  • Wide field of view, for lengthy viewing time of all sources and excellent transient response

  • Discovery reach extending to ~TeV

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Broad spectral coverage 10 GeV 100 GeV 1 TeV is crucial for studying and understanding most astrophysical sources.

GLAST and ground-based experiments cover complimentary energy ranges.

The improved sensitivity of GLAST is necessary for matching the sensitivity of the next generation of ground-based detectors.

GLAST goes a long ways toward filling in the energy gap between space-based and ground-based detectors—there will be overlap for the brighter sources.

Covering the Gamma-Ray Spectrum

Predicted sensitivities to a point source. EGRET, GLAST, and Milagro: 1-yr survey. Cherenkov telescopes: 50 hours on source. (Weekes et al., 1996, with GLAST added)

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Predicted GLAST measurements of Crab unpulsed flux in the overlap region with ground-based atmospheric cherenkov telescopes.

Overlap of GLAST with ACTs

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SNR and Cosmic-Ray Production overlap region with ground-based atmospheric cherenkov telescopes.

EGRET View of the Galactic Anti-center

GLAST Simulation of the Galactic Anti-center

So far, no conclusive results on SNR from EGRET.

Theoretical models and indirect observational evidence support the idea that Galactic CRs are accelerated in the shocks of SNRs.

p0 bump direct evidence of CR nucleai in the Milky Way

IC 443


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Cosmic-Ray Acceleration overlap region with ground-based atmospheric cherenkov telescopes.

GLAST simulations showing SNR -Cygni spatially and spectrally resolved.

Energy (MeV)

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Faint source overlap region with ground-based atmospheric cherenkov telescopes.

EGRET data

Cosmic-Ray Acceleration

Model g-ray spectrum for SNR IC 443 adapted from Baring et al. (1999) illustrating how GLAST can detect even a faint p0-decay component. ( 1 year sky survey with 1 s error bars)

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HST Image of M87 (1994) overlap region with ground-based atmospheric cherenkov telescopes.

Active Galactic Nuclei (AGN)

Active galaxies produce vast amounts of energy (1049 erg/s) from a very compact central volume. Prevailing idea: powered by accretion onto super-massive black holes (106 - 1010 solar masses). Highly variable objects with large fluctuations in luminosity in fractions of a day.

Models include emission of energetic (multi-TeV), highly-collimated, relativistic particle jets. High energy g-rays emitted within a few degrees of jet axis.

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Active Galactic Nuclei overlap region with ground-based atmospheric cherenkov telescopes.

A simple extrapolation from EGRET data suggests that GLAST will detect >5000 AGN, in addition to providing far more detailed data on the known sources.

Simulation of a 1-year all-sky survey by EGRET.

Simulation of a 1-year all-sky survey by GLAST.

E>1 GeV!

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Measurement of AGN Spectra overlap region with ground-based atmospheric cherenkov telescopes.

GLAST will measure blazar quiescent emission and spectral transitions to flaring states.

GLAST should readily detect low-state emission from Mrk 501

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Blazar Cosmology overlap region with ground-based atmospheric cherenkov telescopes.

Roll-offs in the g-ray spectra from AGN at large z probe the extragalactic background light (EBL) over cosmological distances.

A dominant factor in EBL models is the era of galaxy formation:

AGN roll-off may help to distinguish models of galaxy formation, e.g., Cold Dark Matter vs. Hot Dark Matter, neutrino mass contribution, …

Broad spectral coverage and observations of numerous sources will be necessary to reap solid scientific results  map of the correlation between Ecut-off and Z!

The gamma-ray attenuation factor for CDM models using Scalo and Salpeter models.

(Bullock, Somerville, MacMinn, Primack, 1998)

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Identifying Sources overlap region with ground-based atmospheric cherenkov telescopes.

GLAST 95% C.L. radius on a 5 source, compared with a similar EGRET observation of 3EG 1911-2000

EGRET Unidentified Sources

Counting stats not included.

GLAST will make great improvements in our ability to resolve gamma-ray point sources in the galactic plane and to measure the diffuse background.

Cygnus region (150 x 150), Eg > 1 GeV

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Detection of Transients overlap region with ground-based atmospheric cherenkov telescopes.

In scanning mode, GLAST will achieve in one day a sufficient sensitivity to detect (5) the weakest EGRET sources.

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Gamma Ray Bursts overlap region with ground-based atmospheric cherenkov telescopes.

GRBs are the most intense and most distant (z ~ 4.5) known sources of high energy g rays.

With their fast temporal variability GRBs are an extremely powerful tool for probing fundamental physical processes and cosmic history.

Life Extinctions by Cosmic Ray Jets - A. Dar et al. - Physical Review Letters Vol. 80, No.26, 1999

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Gamma-Ray Bursts overlap region with ground-based atmospheric cherenkov telescopes.

Simulated one-year GLAST scan, assuming a various spectral indexes.

1- localization accuracy (arc min.)

  • GLAST will be best suited to studying the GeV tail of the gamma-ray burst spectrum.

  • GLAST should detect 200 GRB per yearwith E>100 MeV, with a third of them localized to better than 10, in real time.

  • Excellent wide field monitor for GRB.Nearly real-time trigger for other wavelength bands, often with sufficient localization for optical follow-up.

  • With a 10s dead time, GLAST will see nearly all of the high-E photons.

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Gamma-Ray Bursts overlap region with ground-based atmospheric cherenkov telescopes.

A separate instrument (NASA-MSFC) on the spacecraft will cover the energy range 10 KeV – 25 MeV and will provide a hard x-ray trigger for GRB.

Energy dependent lags and the physics behind GRB temporal properties will be better studied by the broad energy coverage (10 KeV – 100 GeV) provided by GBM and LAT.

  • The origin of ultra-energy cosmic rays suggested to be GRBS (Waxman 1995)

  • Burst of high energy g as signature of the evaporation of primordial black holes.

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GRBs and Quantum Gravity overlap region with ground-based atmospheric cherenkov telescopes.

GRB ms pulse structure at GeV energies + Gigaparsec distances may constrain

EQuantumGravity ~ 1019 GeV

See: G. Amelino-Camelia, John Ellis, D.V. Nanopoulos et al., Nature 393 (1998) 763-765

Using GLAST, search for possible in vacuo velocity dispersion,

dv ~ E/EQG

of gamma rays from gamma ray bursts at cosmological distances.

For many GRB (EGRET) current best estimate is,

dNg/dEg ~ 1/Eg2

For certain string formulations photon propagation velocity in vacuum appears increased or decreased as energy increases (granularity of space-time)

vg= c(1 ± Eg/EQG+ O[(Eg /EQG)2])

Dt ~ a E/EQG D/c ~ 10 ms GeV-1 Gpc-1 (if EQG ~ 1019 GeV)

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Arrival time distribution overlap region with ground-based atmospheric cherenkov telescopes. for two energy cuts 0.1 GeV and 5 GeV( cross-hatched)

Test of Quantum Gravity

Using only the 10 brightest bursts yr-1, GLAST would easily see the predicted energy- and distance-dependent effect.

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Dark Matter Problem overlap region with ground-based atmospheric cherenkov telescopes.

Experimentally, in spiral galaxies the ratio between the matter density and the Critical density W is :

Wlum ≤ 0.01

but from rotation curves must exist a galactic dark halo of mass at least:

Whalo ≥ 0.03 ÷ 0.1

from gravitational behavior of the galaxies in clusters the

Universal mass density is :

Whalo @ 0.1 ÷ 0.3

from structure formation theories:

Whalo ≥ 0. 3

but from big bang nucleosinthesis the Barionic matter cannot be more then:

WB ≤ 0. 1

M(R) = v2R/G

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Halo WIMP annihilations overlap region with ground-based atmospheric cherenkov telescopes.



gg or Zg





Example: X is c0 from Standard SUSY,

annihilations to jets, producing

an extra component of multi-GeV

g flux that follows halo density (not

isotropic) peaking at ~ 0.1 Mc0

or lines at Mc0. Background is galactic g ray diffuse.



Good particle physics candidate for galactic halo dark matter is the LSP in R-parity conserving SUSY

If true, there may well be

observable halo annihilations

If SUSY uncovered at accelerators, GLAST may be able to determine its cosmological significance quickly.

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Halo WIMP annihilations overlap region with ground-based atmospheric cherenkov telescopes.

Infinite energy resolution

g lines

50 GeV

With finite energy resolution

300 GeV

GLAST two-year scanning mode

Total photon spectrum from the galactic center from cc ann.

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Dark Matter Searches: Neutralino overlap region with ground-based atmospheric cherenkov telescopes.



gg or Zg





q > 50o

GLAST monoenergetic line sensitivity (95% C.L. upper limit) vs. E. Colored areas are a range of MSSMs within a restricted parameter space from standard assumptions and thermal relic abundance calculations.

The GLAST CsI calorimeter will be the largest such device ever put into space. It is only 10 X0 viewed from the front, but from the sides it is up to 1.5 m “thick” and well suited for precision measurements of very high-energy photons.

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Conclusions overlap region with ground-based atmospheric cherenkov telescopes.

  • GLAST is a partnership of HEP and Astrophysics science communities. Forging partnerships between disciplines expands opportunities for doing exciting physics and maximizes the possibility of discoveries.

  • With its large improvement in sensitivity GLAST will allow to observe

  • sources with greater precision and higher statistics

    • increase by orders of magnitude the numbers of visible sources

    • see deeper into the universe

    • monitor continuously the complete, rapidly-changing high-energy gamma-ray sky

    • explore a good portion of the supersymetric parameter space and study the Cold and Hot Dark Matter contribution through the IR absorptionof g-ray from extragalactic sources

    • GRB physics at high energy.

More information on GLAST at