Introduction to gamma-ray astronomy GLAST-Large Area Telescope Introduction to GLAST Science New way of studying astrophysics Schedule of GLAST project Tuneyoshi Kamae SLAC/Hiroshima U. Astrophysics and Particle Physics with Gamma-ray Large Area Space Telescope (GLAST) Gamma-ray Large Area Space Telescope

GLAST LAT Science GLAST LAT Provides: Rapid notification of high-energy transients Detection of several thousand sources, with spectra (20 MeV - > 50 GeV) for several hundred sources Point source localization to 0.3 – 2 arcmin Mapping and spectra of extended sources (e.g., SNRs, molecular clouds, interstellar emission, nearby galaxies) Measurement of the diffuse  -ray background to TeV energies Map the High-Energy Universe 0.01 GeV 0.1 GeV 1 GeV 10 GeV 100 GeV 1 TeV Key Science Questions: What are the mechanisms of particle acceleration in the universe? What are the origins and mechanisms of Gamma-Ray Bursts and other transients? What are the unidentified EGRET Sources? What are the distributions of mass & cosmic-rays in the galaxy and in nearby galaxies? How can high-energy  -rays be used to probe the early universe? What is the nature of dark matter? FOV w/ energy measurement due to favorable aspect ratio Effects of longitudinal shower profiling More than 40 times the sensitivity of EGRET Large Effective Area (20 MeV – 1 TeV) Optimized Point Spread Function ( GeV) Wide Field of View (2.4 sr) Good Energy Resolution (  E/E ~ 10%) GLAST LAT Performance

History of Gamma-ray Astrophysics OSO-III (1967): Prop. Counter, Hint of Galactic diffuse emission SAS-2 (1972): Spark ch., Galactic diffuse emission, ~10 Galactic sources COS-B (1975): Spark ch., extended to E~2GeV, ~25 sources including an extragalactic source (3C273) EGRET(1991): Spark ch., extended to E~10GeV, ~271 sources including ~170 unidentified sources and a millisecond pulsar. 5 GRBs detected Ground-based Cherenkov Telescopes (~1993): Whipple, Cangaroo, and others detected gamma-rays from ~10 sources including Crab, SN1006, and bright AGNs Comparison with X-ray Astronomy: X-ray Telescope Gamma-ray (EGRET) Detection technology focusing mirror, CCD e+e- pair creation tracking Sensitivity a few micro-Crab ~ ten milli-Crab Angular resolution < 1 arc-second <1 degree No. of Sources detected >>10 6 ~300

Universe is Transparent to Gamma-rays X-ray is absorbed by ISM, VHE gamma-ray by Extragalactic Background Light (EBL) and Cosmic Microwave Background. But Universe is quite transparent to gamma-rays in the energy band of GLAST. GLAST will keep unique ability to reach out to z>>10, and if fortunate, will give us chance to make a few serendipitous discoveries.

Photon Energy Spectra of Cosmic Sources

Point source contribution (AGN + pulsars etc.) Diffuse emission from cosmic-ray interaction with ISM in galaxies and clusters of galaxies Decay and annihilation of heavy particles (particle dark matter?) Cosmic Diffuse Background Universe Is Filled with Gamma-ray - Isotropic Diffuse Background - Energy per decade Energy in log scale GLAST X-ray Hard X Soft 

Detector Technology: X-ray vs. Gamma-ray X-ray ( keV) Focusing possible Large effective area Excellent energy resolution Very low background Narrow view Gamma-ray( GeV) No focusing possible Wide field of view Limited effective area Moderate energy resolution High background

New Detector Technology Silicon strip detector –Idea and first implementation: Kemmer et al (late 1970s) –Commercial suppliers in Japan, UK, Switzerland, and Italy Strip-shaped PN diode micron wide micron thick VLSI amplifier Stable particle tracker that allows micron-level tracking of gamma-rays

EGRET(Spark Chamber) VS. GLAST(Silicon Strip Detector) EGRET on Compton GRO ( ) GLAST Large Area Telescope ( )

 e+e+ e–e– 16 towers  modularity height/width = 0.4  large field-of-view GLAST Large Area Telescope (LAT) Design Instrument Pair-conversion telescope Tracker Modules  e+e+ e–e– 16 towers  modularity height/width = 0.4  large field-of-view Si-strip detectors: fine pitch: 236  m, high efficiency 12 front tracking planes (x,y): 0.45 X o reduce multiple scattering 4 back tracking planes (x,y): 1.0 X o increase sensitivity > 1 GeV One of 18 Tracker trays (detectors top & bottom)

 e+e+ e–e– 16 towers  modularity height/width = 0.4  large field-of-view GLAST Large Area Telescope (LAT) Design Instrument Pair-conversion telescope Calorimeter Modules 8.5 rl Compression Cell Design Mechanical Prototype of Carbon Cell Design Hodoscopic Imaging Array of CsI crystals: ~ 8.5 rl depth PIN photodiode readout from both ends: 2 ch/xtal x 80 xtals/mod = 2,560 ch segmentation allows pattern recognition (“imaging”) and leakage correction 16 towers  modularity height/width = 0.4  large field-of-view

 e+e+ e–e– 16 towers  modularity height/width = 0.4  large field-of-view GLAST Large Area Telescope (LAT) Design Instrument Pair-conversion telescope Anticoincidence Shield Segmented, plastic scintillator tile array: high efficiency, low-noise, hermetic; segment ACD sufficiently and only veto event if a track points to hit tile 16 towers  modularity height/width = 0.4  large field-of-view ACD tile readout with Wavelength Shifting Fiber

GLAST Large Area Telescope (LAT) Design 16 towers  modularity height/width = 0.4  large field-of-view Si-strip detectors: 236 mm pitch, total of 8.8 x 10 5 ch. hodoscopic CsI crystal array  cosmic-ray rejection  shower leakage correction X Tkr + Cal = 10 X 0  shower max contained < 100 GeV segmented plastic scintillator  minimize self-veto > efficiency & redundant readout Instrument Tracker Calorimeter Anticoincidence Shield