GLAST:Gamma Ray Large Area Telescope

1
GLASTGamma Ray Large Area Telescope
The GLAST Mission and its Physics
reach R.Bellazzini INFN - sez. Pisa
2
Nature's Highest Energy Particle Accelerators
OUTLINE Introduction Pair-Conversions
Telescopes The LAT Design LAT Performance GLAST
Science Topics Conclusions
3
Profound Connection between Astrophysics HEP
The fundamental theory of Cosmic Genesis and the
quest for experimental evidence has 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.
4
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 gt 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

5
GLAST Science
Map the High-Energy Universe
Supernova Remnants
AGN

• 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.

6
Pair-Conversion Telescope
Photons materialize into matter-antimatter pairs
E? -gt mec2 me-c2

• GLAST Concept
• 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)

7
The Large Area Telescope (LAT)

• 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.

8
The LAT Hardware
9
Tray assembling

• Trays are C-composite panels (Al hexcel core)
• Carbon-fiber walls provide stiffness and the
  thermal
• pathway from electronics to the grid.

10
GLAST Tracker Design Overview

• 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

11
Prototyping of the GLAST SSD
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)
12
International Collaboration

• 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
13
Project schedule
SSD Procurement
Ladder Production
Tray Assembly
14
LAT Instrument Performance
Including all Background Track Quality Cuts
15
GLAST Science Capability

• Key instrument features that enhance GLASTs
  science reach
• Peak effective area 12,900 cm2
• Precision point-spread function (lt0.10 for E10
  GeV)
• Excellent background rejection better than
  2.5?1051
• Good energy resolution for all photons (lt10)
• Wide field of view, for lengthy viewing time of
  all sources and excellent transient response
• Discovery reach extending to TeV

16
Covering the Gamma-Ray Spectrum

• Broad spectral coverage 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
  detectorsthere will be overlap for the brighter
  sources.

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)
17
Overlap of GLAST with ACTs

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

18
SNR and Cosmic-Ray Production
EGRET View of the Galactic Anti-center
GLAST Simulation of the Galactic Anti-center
Geminga
IC 443
Crab
So far, no conclusive results on SNR from EGRET.

• GLAST will provide
• detailed maps of the galactic diffuse gamma-ray
  emission.
• measurements of SNR spectra.
• resolved SNR shells at ?10? level.
• detailed maps of emission from galactic molecular
  clouds.

• In order to
• locate SNR in the galactic plane.
• determine whether SNR could be the source of
  cosmic rays.
• map the distribution of cosmic rays in the galaxy.

19
Cosmic-Ray Acceleration
Energy (MeV)

• GLAST simulations showing SNR ?-Cygni spatially
  and spectrally resolved.

20
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)
21
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.
22
Active Galactic Nuclei
Simulation of a 1-year all-sky survey by EGRET.
Simulation of a 1-year all-sky survey by GLAST.
Egt1 GeV!
23
Measurement of AGN Spectra
GLAST will measure blazar quiescent emission and
spectral transitions to flaring states.

• GLAST should readily detect low-state emission
  from Mrk 501

24
Blazar Cosmology
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)
25
Identifying Sources
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 gt 1 GeV
26
Detection of Transients
In scanning mode, GLAST will achieve in one day a
sufficient sensitivity to detect (5?) the weakest
EGRET sources.
27
Gamma Ray Bursts
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
28
Gamma-Ray Bursts

• GLAST will be best suited to studying the GeV
  tail of the gamma-ray burst spectrum.
• GLAST should detect ?200 GRB per year with Egt100
  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.

29
Gamma-Ray Bursts
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.

30
GRBs and Quantum Gravity
GRB ms pulse structure at GeV energies
Gigaparsec distances may constrain EQuantum
Gravity 1019 GeV See G. Amelino-Camelia,
John Ellis 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)
31
Test of Quantum Gravity
Using only the 10 brightest bursts yr-1, GLAST
would easily see the predicted energy- and
distance-dependent effect.
32
Dark Matter Problem
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 _at_ 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
33
Halo WIMP annihilations
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.
34
Halo WIMP annihilations
Total photon spectrum from the galactic center
from cc ann.
35
Dark Matter Searches Neutralino
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.
36
Conclusions

• 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 http//www.pi.infn.it
/glast