Introduction to gamma-ray astronomy GLAST-Large Area Telescope Introduction to GLAST Science New way of studying astrophysics Schedule of GLAST project

Tuneyoshi KamaeSLAC/Hiroshima U.

Astrophysics and Particle Physics withGamma-ray Large Area Space Telescope

(GLAST)

Gamma-ray Large Area Space Telescope

GLAST LAT ScienceGLAST 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(0.35o @ 1 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 >>106 ~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 -

En

ergy

per

dec

ade

Energy in log scale

GLASTX-ray

Hard X Soft

Detector Technology: X-ray vs. Gamma-ray

X-ray (0.5 - 10keV)Focusing possible

Large effective area Excellent energy resolution Very low background Narrow view

Gamma-ray(0.1-500GeV)No focusing possible

Wide field of viewLimited 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-shapedPN diode

50-500micron wide

300-500micron 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 (1991-2000)

GLAST Large Area Telescope (2005-2015)

e+ e–

16 towers modularity

height/width = 0.4 large field-of-view

GLAST Large Area Telescope (LAT) Design

InstrumentPair-conversion telescope

Tracker Modules

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 Xo

reduce multiple scattering

4 back tracking planes (x,y): 1.0 Xo

increase sensitivity > 1 GeV

One of 18 Tracker

trays(detectors top

& bottom)

e+ e–

16 towers modularity

height/width = 0.4 large field-of-view

GLAST Large Area Telescope (LAT) Design

InstrumentPair-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–

16 towers modularity

height/width = 0.4 large field-of-view

GLAST Large Area Telescope (LAT) Design

InstrumentPair-conversion telescope

Anticoincidence ShieldSegmented, 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 105 ch.

hodoscopic CsI crystal array cosmic-ray rejection shower leakage correction XTkr + Cal = 10 X0 shower max

contained < 100 GeV

segmented plastic scintillator minimize self-veto > 0.9997 efficiency & redundant readout

Instrument

Tracker

Calorimeter

Anticoincidence Shield