1. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-11 GLAST Large Area Telescope: Project Overview Robert P. Johnson Santa Cruz Institute for Particle Physics Physics Department University of California at Santa Cruz LAT Tracker Subsystem Manager Representing the LAT Collaboration rjohnson@scipp.ucsc.edu Gamma-ray Large Area Space Telescope

2. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-12 Gamma-ray Large Area Space Telescope GLAST Mission  High-energy gamma-ray observatory with 2 instruments:  Large Area Telescope (LAT)  Gamma-ray Burst Monitor (GBM)  Launch vehicle: Delta-2 class  Orbit: 550 km, 28.5 o inclination  Lifetime: 5 years (minimum) GLAST Gamma-Ray Observatory: LAT ~20 MeV and up GBM 20 keV to 20 MeV Spacecraft bus (Spectrum Astro) LAT GBM

3. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-13 GLAST Science Opportunities  Active Galactic Nuclei  Isotropic Diffuse Background Radiation  Endpoints of Stellar Evolution  Neutron Stars/Pulsars  Black Holes  Cosmic Ray Production:  Identify sites and mechanisms  Unidentified Gamma-ray Sources  Gamma-Ray Bursts  Dark Matter  Solar Physics  DISCOVERY!

4. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-14 Scientific Heritage: CGRO-EGRET Cygnus Region 3C279 Geminga Vela Cosmic Ray Interactions With ISM LMC PKS 0528+134 PKS 0208-512 Crab PSR B1706-44 EGRET All-Sky Map (E> 100MeV)

5. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-15 3 rd EGRET Source Catalog  271 sources  172 sources are unidentified

6. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-16 LAT Source Catalogs M31 > 1 GeV GRB, AGN, 3EG + Gal. plane & halo sources LAT Catalog: ~10,000 sources expected. 5  sources from a simulated 1-year all-sky survey.

7. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-17 LAT Science Capabilities - Resolution Source localization (68% radius):  bursts 1 to tens of arcmin Unidentified EGRET sources 0.3’ to 1’ > 1 GeV M31 > 1 GeV Unidentified EGRET Sources Cygnus region (15 0 x 15 0 ), E  > 1 GeV Greatly improved source localization, continuous monitoring of transient behavior, and rapid GRB notification will aid the search for counterparts and the identification of sources and bursts.

8. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-18 Pair-Conversion Telescope Principle Veto counters: a signal indicates presence of a charge cosmic ray, instead of a photon. Tracker/Converter: heavy metal converts the photon to a positron-electron pair. The measured tracks point back to the astronomical source. Calorimeter: measures the photon energy

9. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-19 GLAST LAT Overview: Design e+e+ e–e–  Si Tracker 8.8  10 5 channels <160 Watts 16 tungsten layers 36 SSD layers Strip pitch = 228 µm Self triggering Grid (& Thermal Radiators) Data acquisition 3000 kg, 650 W (allocation) 1.8 m  1.8 m  1.0 m 20 MeV – 300 GeV CsI Calorimeter Hodoscopic array 8.4 X 0 8 × 12 bars 2.0 × 2.7 × 33.6 cm  cosmic-ray rejection  shower leakage correction ACD Segmented scintillator tiles 0.9997 efficiency Minimal self veto Mega-channel particle-physics detector in orbit:  Low power (<650 W)!  Extensive data reduction on orbit!  No maintenance!

10. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-110 GLAST LAT Overview: Performance e+e+ e–e–  Point Source Sensitivity: < 6 x 10 -9 ph cm -2 s -1 (est. performance: < 3 x 10 -9 ph cm -2 s -1 ) ~40 times EGRET’s sensitivity Single Photon Angular Resolution: 3.5 o @ 100 MeV 0.15 o @ 10 GeV Large Effective Area (A eff ) peak > 8,000 cm 2 Wide Field of View (> 2 sr) Good Energy Resolution  E/E ~ 10%; 100 MeV – 10 GeV ~ < 20%; 10 GeV – 300 GeV Low dead time: < 100  s/event Wide Energy Range: 20 MeV - >300 GeV

11. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-111 Anti-Coincidence Detector (NASA GSFC) Scintillator & Wave-Shifting Fibers Readout Electronics Scintillator Tiles Fibers Composite Shell Photomultiplier Tubes & Electronics LAT Mechanical Structure (SLAC) Fermilab Tile detector assembly 2 PMTs

12. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-112 ACD Performance Charged Particles (MIP) Backsplash + noise Requirement Measurement Threshold setting of 0.3 MIP achieves the required efficiency (>0.9997) with low noise. Backsplash self-veto measurements (made at CERN) indicate good margin with respect to requirements.

13. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-113 Silicon-Strip Tracker/Converter Flex- Circuit Readout Cables 36 Multi-Chip Electronics Modules (MCM) 2 mm gap between x,y SSD layers 19 Carbon-Fiber Tray Panels Titanium Flexure Mounts Carbon-Fiber Sidewalls (Aluminum covered) Cu Thermal Strap M55J/CC Closeouts Ti Reinforced Corners  19 stiff composite panels support 18 x and 18 y layers of silicon-strip detectors and 16 layers of tungsten converter foils.  36 custom readout electronics boards, each with 1536 amplifier channels, mount on the sides of the panels to minimize inter-tower dead space.

14. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-114 Tracker Production Overview Readout Cables UCSC, SLAC (Parlex) SSD Procurement, Testing Japan, Italy (HPK) Electronics Fabrication, burn-in, & Test UCSC, SLAC (Teledyne) Tracker Module Assembly and Test Italy (Alenia Spazio) Tray Assembly and Test Italy (G&A) SSD Ladder Assembly Italy (G&A, Mipot) Composite Panel, Converters, and Bias Circuits Italy (Plyform): fabrication SLAC: CC, bias circuits, thick W, Al cores 2592 10,368 342 648 18 Module Structure Components SLAC: Ti parts, thermal straps, fasteners. Italy (Plyform): Sidewalls 342

15. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-115 Calorimeter CsI Crystals (Sweden) Photo-Diodes (HPK) Detector Assembly (NRL/Swales) C-Composite Structure (France) Electronics & Assembly (NRL) 1728 3456 1728 18

16. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-116 Data Acquisition Electronics (SLAC) LAT Mockup (upside down) Power Supply (PS) Tower Electronics Module (TEM) 16 PS 16 TEM Power Spacecraft Interface Event Processors  Detector Systems Thermal Radiator Global Trigger & Signal Distribution

17. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-117 LAT Structural/Thermal Design Aluminum Grid Grooves for heat pipes Radiator Variable conductance heat pipes Spacecraft Rocket Shroud More heat pipes on bottom plate directly connect the 2 radiators

18. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-118 Engineering Model Hardware Prototypes completed this year, for functional and environmental testing. Tracker (partial) Calorimeter TEM Tracker

19. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-119 Example Engineering Model Cosmic-Ray 6 Tracker Layers Instrumented Fully Instrumented Calorimeter

20. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-120 Sample Engineering Model Results Calorimeter Muon Energy Deposition Calorimeter Muon Position Resolution 0.4 cm rms Track Polar Angle, cosmic rays Tracker Ionization Measurement (TOT), cosmic rays (From a single crystal)

21. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-121 GLAST-LAT Schedule 200020012002200320042005 Formulation Implementation PDR CDR (Joint DOE/NASA Review) Begin LAT-S/C Integration Launch Build & Test Flight Units Inst. I&T Schedule Reserve Observatory I&T 1 st Joint DOE/NASA Review of GLAST LAT 2006 Build & Test Engineering Models LAT integration and functional test at SLAC. LAT environmental test at NRL (Washington). Spacecraft vendor: Spectrum Astro (Arizona). LAT-Spacecraft integration & test in Arizona. Launch at Cape Canaveral, Florida.

22. GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-122 Conclusions  The LAT is presently wrapping up engineering model work and design engineering and is starting into flight-hardware production.  The LAT is a large detector array with unprecedented channel count and computing power for a space-based experiment.  The LAT will be our eye into the gamma-ray sky in the energy range from about 50 MeV to 50 GeV and will complement and work together with new ground based detectors sensitive only to higher energies (HESS, Magic, Veritas, etc.).  Working together with telescopes for all other wavelengths, GLAST will help to answer many puzzling questions in astrophysics and related particle physics by observing many of the most energetic and enigmatic objects in the universe.  By using modern detector and computing technology, GLAST will greatly surpass the sensitivity of previous high-energy gamma-ray telescopes, providing us with exciting discovery potential.