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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The GLAST Mission
and its Physics reach
INFN - sez. Pisa
The LAT Design
GLAST Science Topics
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.
This quest is changing the face of both fields.
First Came EGRET
Raised many interesting issues andquestions which can be addressed by a NASA mid-class mission (Delta II).
Launched in April 1991
0.01 GeV 0.1 GeV 1 GeV 10 GeV 100 GeV 1 TeV
Area (square cm)
0.01 0.1 1 10 100 1000
Map the High-Energy Universe
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.
Low power consumption (580 W)Pair-Conversion Telescope
Charged particle anticoincidence shield
Particle tracking detectors
Photons materialize into matter-antimatter pairs:
E -> me+c2 + me-c2
One Tracker Tower Module
Carbon thermal panel
Electronics flex cables
Preserie HPK detector
on 6’’ wafer
Gained experience with a large number of SSD (~5% of GLAST needs)
Micron (UK), STM (Italy), CSEM (Switzerland)
for multi-wavelength observations
~ 100 collaborators
from 28 institutions
Build & Test
Build & Test
Including all Background & Track Quality Cuts
Key instrument features that enhance GLAST’s science reach:
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)
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
GLAST simulations showing SNR -Cygni spatially and spectrally resolved.
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)
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.
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.
GLAST will measure blazar quiescent emission and spectral transitions to flaring states.
GLAST should readily detect low-state emission from Mrk 501
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)
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
In scanning mode, GLAST will achieve in one day a sufficient sensitivity to detect (5) the weakest EGRET sources.
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
Simulated one-year GLAST scan, assuming a various spectral indexes.
1- localization accuracy (arc min.)
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.
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)
Arrival time distribution 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.
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
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.
Infinite energy resolution
With finite energy resolution
GLAST two-year scanning mode
Total photon spectrum from the galactic center from cc ann.
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.
More information on GLAST at http://www.pi.infn.it/glast