GLAST LAT Project
Gamma-ray Large
Area Space
Telescope
DOE Rebaseline Review, February 18, 2005
GLAST Large Area Telescope:
Introduction
Peter F. Michelson
Stanford/SLAC
LAT Principal Investigator
S. Ritz
Goddard Space Flight Center
GLAST Project Scientist and LAT Instrument Scientist
steven.m.ritz@nasa.gov
301-286-0941
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Why study g’s?
– g rays offer a direct view into Nature’s largest accelerators.
– the Universe is mainly transparent to g rays: can probe cosmological
volumes. Any opacity is energy-dependent.
– conversely, g rays readily interact
in detectors, with a clear signature.
Large Area Telescope
– g rays are neutral: no complications
(LAT)
due to magnetic fields. Point
directly back to sources, etc.
Two GLAST instruments:
LAT: 20 MeV – >300 GeV
GBM: 10 keV – 25 MeV
Launch: 2007
5-year mission (10-year goal)
spacecraft partner:
GLAST Burst Monitor
(GBM)
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
GLAST Science
GLAST will have a very broad menu that includes:
• Systems with supermassive black holes (Active Galactic Nuclei)
• Gamma-ray bursts (GRBs)
• Pulsars
• Solar physics
• Origin of Cosmic Rays
• Probing the era of galaxy formation, optical-UV background light
• Solving the mystery of the high-energy unidentified sources
• Discovery! Particle Dark Matter? Other relics from the Big Bang?
Testing Lorentz invariance. New source classes.
Huge increment in capabilities.
GLAST draws the interest of both the the High Energy Particle
Physics and High Energy Astrophysics communities.
GLAST is the highest-ranked initiative in its category in the
National Academy of Sciences 2000 Decadal Survey Report.
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
GLAST LAT High Energy Capabilities
EGRET on CGRO firmly established the field of high-energy gamma-ray
astrophysics and demonstrated the importance and potential of this energy
band.
GLAST is the next great step beyond EGRET, providing a huge leap in
capabilities:
• Very large FOV (~20% of sky), factor 4 greater than EGRET
• Broadband (4 decades in energy, including unexplored region E > 10 GeV)
• Unprecedented PSF for gamma rays (factor > 3 better than EGRET for
E>1 GeV)
• Large effective area (factor > 5 better than EGRET)
• Results in factor > 30 improvement in sensitivity
• Much smaller deadtime per event (25 microsec, factor >4,000 better than
EGRET)
• No expendables
long mission without degradation
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Sources
EGRET 3rd
Catalog: 271
sources
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Sources
LAT 1st Catalog:
>9000 sources
possible
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Galactic Anticenter Region
simulation: S. Digel
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
GLAST LAT Collaboration
United States
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California State University at Sonoma
University of California at Santa Cruz - Santa Cruz Institute of Particle Physics
Goddard Space Flight Center – Laboratory for High Energy Astrophysics
Naval Research Laboratory
Ohio State University
Stanford University (SLAC and HEPL/Physics)
University of Washington
Washington University, St. Louis
France
PI: Peter Michelson (Stanford & SLAC)
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~120 Members (including ~60 Affiliated
Scientists, plus 20 Postdocs, and 25
Graduate Students)
IN2P3, CEA/Saclay
Italy
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INFN, ASI
Japanese GLAST Collaboration
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Hiroshima University
ISAS, RIKEN
Swedish GLAST Collaboration
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Cooperation between NASA and DOE, with
key international contributions from
France, Italy, Japan and Sweden.
Managed at Stanford Linear Accelerator
Center (SLAC).
Royal Institute of Technology (KTH)
Stockholm University
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Overview of LAT
g
• Precision Si-strip Tracker (TKR)
18
XY tracking planes. Single-sided silicon
strip detectors (228 mm pitch) Measure
the photon direction; gamma ID.
Tracker
• Hodoscopic CsI Calorimeter(CAL)
Array of 1536 CsI(Tl) crystals in 8 layers.
Measure the photon energy; image the
shower.
• Segmented Anticoincidence Detector
(ACD) 89 plastic scintillator tiles.
Reject background of charged cosmic
rays; segmentation removes self-veto
effects at high energy.
• Electronics System Includes flexible,
robust hardware trigger and software
filters.
ACD
[surrounds
4x4 array of
TKR towers]
e+
e–
Calorimeter
Systems work together to identify and measure the flux of cosmic gamma
rays with energy 20 MeV - >300 GeV.
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Design Performance Validation:
LAT Monte-Carlo Model
The LAT design is based on detailed
Monte Carlo simulations.
Integral part of the project from the
start.
 Background rejection
 Calculate effective area and
resolutions.
 Trigger design.
 Overall design optimization.
 Impacts of failures.
 Science simulations.
Simulations and analyses are all C++,
based on standard HEP packages.
Model validated in a sequence of
beam test measurements.
Detailed detector
model includes
gaps, support
material, thermal
blanket, simple
spacecraft, noise,
sensor responses…
Instrument naturally distinguishes gammas
from backgrounds, but details matter.
gamma ray
proton
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Monte Carlo Modeling Verified in Detailed Beam Tests
Experimental setup in ESA
for tagged photons:
X Projected Angle
3-cm spacing, 4% foils, 100-200 MeV
Data
Containment Space Angle (deg)
Monte
Carlo
GLAST Data
68% Containment
95% Containment
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(errors are 2)
1
Monte
Carlo
0.1
101
102
103
Energy (MeV)
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Published in NIM A446(2000), 444.
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
1999-2000 Beam Test at SLAC
Using beams of positrons, tagged photons and hadrons,
with a ~flight-size tower, studies of
Published in NIM A474(2001)19.
• data system, trigger
• hit multiplicities in
front and back tracker
sections
• calorimeter response
with prototype
electronics.
• time-over-threshold in
silicon
• upper limit on neutron
component of ACD
backsplash
• hadron tagging and
first look at response
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Data Challenges
• Early alpha-testing. “End-to-end” testing of analysis software.
• Provide feedback on what works and what is missing from the data
formats and tools.
• Walk before running: design a progression of studies.
– DC1. Modest goals. Contains most essential features of a data
challenge.
• 1 simulated day all-sky survey simulation
• find the sources, including GRBs
• a few physics surprises
• exercise:
– exposure, orbit/attitude handling, data processing pipeline components,
analysis tools
– DC2 in 2005. More ambitious goals. ~One simulated month.
• toy one-month catalog.
• add source variability (AGN flares, pulsars). add GBM.
– DC3 in 2006. Support for flight science production.
see http://www-glast.slac.stanford.edu/software/Workshops/Feb04DC1CloseOut/coverpage.htm
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
The DC1 Sky
One day all-sky survey. Generated E>20 MeV.
E>100 MeV
with some other cuts
for illustration
Lots to analyze!
A few surprises to find…
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Data Challenge 1 Sky
3C273
isotropic diffuse
3C279
Sources – 3EG and more, with a twist
a number of physics
surprises in the DC1
data, including:
• 110 GeV gamma-ray
line source at the
galactic center
• new source populations
• and…
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Operations Phase LAT Organization Chart
 Dr. Rob Cameron appointed LAT
Instrument Science Operations Center
manager
– extensive operations experience at
SAO / Chandra X-ray Center
 LAT Collaboration Science Groups (LSGs)
responsible for collaboration’s analysis
and extraction of science results from LAT
data
– 11 Science Groups plus Multi-l
Coordination Working Group
– each science group to have 2 coleads; with one resident at Stanford
– day-to-day efforts coordinated by
Analysis Coordinator, also resident at
Stanford-SLAC
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Science Analysis Groups
 groups organized around expected collaboration publications, particularly
during the 1st year all-sky survey phase; each group should have responsibility
for 2-3 key (category 1) papers (see Plan posted on meeting Website)
Science Analysis Groups
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11.
Catalogs
Galactic Diffuse and Molecular Clouds
Extragalactic Diffuse
Blazars and Other AGNs
Other Galaxies (including clusters)
Pulsars, SNRs, and Plerions
Unidentified Sources and Population Studies
Dark Matter and Exotic Physics
Gamma-Ray Bursts
Solar System Sources
Calibration and Analysis Methods
LAT Multiwavelength Observation Coordination Group
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Next LAT Collaboration Meeting
SLAC, March 8-10, 2005
• further develop collaboration plans for LAT I&T data analysis
• updates on status of flight hardware development and
Instrument integration and test
• advance the planning for the science operations and analysis
phase
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initial meetings of Collaboration Science Analysis Groups
update on Instrument Science Operations Center plans and needs
advance the planning for data challenge II
update on software development
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Possible Descope
• With increasing budget pressures, NASA HQ has asked the
LAT team and GLAST Project to assess the science impact of
removing the four corner TKR towers.
– cost savings generated by schedule reduction of
approximately one month
– briefing to Anne Kinney on 24 February in preparation
– a number of breakthrough science topics significantly
affected
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GLAST LAT Project
DOE Rebaseline Review, February 18, 2005
Summary
• Flight hardware is being delivered (see Lowell’s talk)
– great excitement in the team
• Integration and Test activities ramping up
• Preparation for science operations and science analysis
underway.
• Continuing support during this difficult budget time is deeply
appreciated by the team.
– the science payoff will be great!
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