1. GLAST Large Area Telescope:
Gamma-ray Large Area Space Telescope
GLAST Large Area Telescope:
Peter F. Michelson
Stanford/SLAC
LAT Principal Investigator
S. Ritz
Goddard Space Flight Center
GLAST Project Scientist and LAT Instrument Scientist
Introduction

2. 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.
g rays are neutral: no complications 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)
Large Area Telescope (LAT)
spacecraft partner:
GLAST Burst Monitor (GBM)

3. 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.

4. 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

5. Sources
EGRET 3rd Catalog: 271 sources

6. Sources
LAT 1st Catalog:
>9000 sources possible

7. Galactic Anticenter Region
simulation: S. Digel

8. GLAST LAT Collaboration
United States
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
IN2P3, CEA/Saclay
Italy
INFN, ASI
Japanese GLAST Collaboration
Hiroshima University
ISAS, RIKEN
Swedish GLAST Collaboration
Royal Institute of Technology (KTH)
Stockholm University
PI: Peter Michelson (Stanford & SLAC)
~120 Members (including ~60 Affiliated Scientists, plus 20 Postdocs, and 25 Graduate Students)
Cooperation between NASA and DOE, with key international contributions from France, Italy, Japan and Sweden.
Managed at Stanford Linear Accelerator Center (SLAC).

9. Overview of LAT  e+ e– Tracker
Precision Si-strip Tracker (TKR) XY tracking planes. Single-sided silicon strip detectors (228 mm pitch) Measure the photon direction; gamma ID.
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.
Tracker
ACD [surrounds 4x4 array of TKR towers]
Calorimeter
Systems work together to identify and measure the flux of cosmic gamma rays with energy 20 MeV - >300 GeV.

10. Design Performance Validation: LAT Monte-Carlo Model
Detailed detector model includes gaps, support material, thermal blanket, simple spacecraft, noise, sensor responses…
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.
Instrument naturally distinguishes gammas from backgrounds, but details matter.
proton
gamma ray

11. Monte Carlo Modeling Verified in Detailed Beam Tests
Experimental setup in ESA for tagged photons:
X Projected Angle
3-cm spacing, 4% foils, MeV
Data
Monte Carlo
GLAST Data
(errors are 2)
Monte Carlo
Published in NIM A446(2000), 444.

12. Beam Test at SLAC
Using beams of positrons, tagged photons and hadrons, with a ~flight-size tower, studies of
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
Published in NIM A474(2001)19.

13. 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 More ambitious goals. ~One simulated month.
toy one-month catalog.
add source variability (AGN flares, pulsars). add GBM.
DC3 in Support for flight science production.
see

14. A few surprises to find…
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…

15. Data Challenge 1 Sky a number of physics surprises in the DC1
isotropic diffuse
a number of physics
surprises in the DC1
data, including:
110 GeV gamma-ray line source at the galactic center
new source populations
and…
Sources – 3EG and more, with a twist

16. 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 co-leads; with one resident at Stanford
day-to-day efforts coordinated by Analysis Coordinator, also resident at Stanford-SLAC

17. 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
1. Catalogs
2. Galactic Diffuse and Molecular Clouds
3. Extragalactic Diffuse
4. Blazars and Other AGNs
5. Other Galaxies (including clusters)
6. Pulsars, SNRs, and Plerions
7. Unidentified Sources and Population Studies
8. Dark Matter and Exotic Physics
9. Gamma-Ray Bursts
10. Solar System Sources
11. Calibration and Analysis Methods
LAT Multiwavelength Observation Coordination Group

18. 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
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

19. 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

20. 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!