Gamma-Ray Telescopes

Brief History of Gamma Ray Astronomy

1961 EXPLORER-II: First detection of high-energy -rays from space

1967 VELA satelllites: Discovery of -ray bursts (not published until 1973)1968 OSO-3: Discovery of > 100 MeV -ray emission from the Milky Way

1972 SAS-2: First high-energy -ray images; discovery of Geminga pulsar

1975 COS-B: First detailed -ray map of the Milky Way with 24 point sources1979 HEAO-3: Discovery of radioactive 26Al emission in the Milky Way

1981 SMM: Studies of solar flare -ray emission; 56Co-lines from SN 1987A

1987 Whipple (ACT): First credible detection of a TeV source (Crab Nebula)1989 SIGMA: First high-resolution images (13’) in hard X-rays / soft -rays

1991 CGRO: First all-sky survey of the -ray sky; major discoveries in all areas of -ray astronomy; -ray astronomy becomes an integral part of astronomy

1997 BeppoSAX: First high-precision localization of -ray bursts; cosmological origin of GRBs established

2002 INTEGRAL: Major advances in high-resolution imaging and spectroscopy of Galactic -ray sources

2004 Swift: Dedicated -ray burst mission: prompt X-ray/optical follow-up; arcsecond localization of GRBs

2008 Fermi (GLAST): All-sky monitoring of the MeV – GeV sky every 3 hr with sensitivity a factor of > 10 better than EGRET.

1) The Compton Gamma Ray Observatory (CGRO)

(1991 – 2000)

Oriented Scintillation-Spectrometer Experiment (OSSE): ~ 0.1 – 10 MeV

Compton Telescope (COMPTEL): ~ 1 – 30 MeV

Energetic Gamma-Ray Experiment Telescope

(EGRET): pair conversion telescope,

~ 20 MeV – 30 GeV

Burst and Transient Source Experiment (BATSE):

0.015 – 110 MeV

2) The International Gamma-Ray Astrophysics Laboratory (INTEGRAL)

Launched 2002

Two -ray telescopes:

Imager on Board the INTEGRAL Satellite (IBIS), optimized for high spatial

resolution;

Spectrometer on INTEGRAL (SPI), optimized for high

spectral resolution.

Energy range: ~ 20 keV – 8 MeV

Both use coded-mask technique for imaging.

3) AGILE(Astro-rivelatore Gamma a Immagini LEggero)

Similar technology and capabilities as EGRET, intended to bridge the gap

between EGRET and Fermi (GLAST)

Italian gamma-ray satellite mission; launched April 23, 2007

Two instruments:

Gamma-Ray Imaging

Detector (GRID):

30 MeV – 50 GeV

SuperAGILE:

18 – 60 keV

4) The Fermi Gamma-Ray Space Telescope (formerly: Gamma Ray Large Area Space Telescope

(GLAST)Launched June 11, 2008

Similar technology as EGRET (pair conversion), but much

improved sensitivity, large field of view (~ sr), and slightly

extended energy range (~ 20 MeV – 300 GeV).

Will operate in constant slewing mode to survey the

sky for flaring high-energy -ray sources:

One full-sky scan every 3 hr.

Fermi

Two main science instruments:

• LAT (Large Area Telescope)

• GBM (GLAST Burst Monitor)

The Large Area Telescope (LAT)Pair Conversion Telescope

Quantity LAT EGRET

Energy Range 20 MeV – 300 GeV 20 MeV – 30 GeV

Peak Effective Area > 8000 cm2 1500 cm2

Field of View > 2 sr 0.5 sr

Angular Resolution < 3.5o (at 100 MeV)

< 0.15o (at > 10 GeV)

5.8o (at 100 MeV)

Point Source Sensitivity < 6*10-9 cm-2 s-1 10-7 cm-2 s-1

The LAT First-Light All-Sky Map

All-Sky Map

The GLAST Burst Monitor (GBM)All-sky Monitor optimized to detect X-ray / soft -ray

flashes(~ 8 keV – 30 MeV)

Source localization to < 15o

5) Atmospheric Cherenkov Telescopes

Experiment Technique Ethr (TeV) Location

Whipple IACT 0.25 Arizona, USA

HEGRA-IACT IACT array 0.50 Canary Islands

CANGAROO-II IACT 0.1 Woomera, Australia

HEGRA-AIROBICC Wavefront sampling

15 Canary Islands

Themistocle Wavefront sampling

3 Themis, France

STACEE Solar Tower ACT 0.05 Albuquerque, NM, USA

HESS IACT array 0.04 Gamsberg, Namibia

MAGIC IACT 0.01 Canary Islands

VERITAS IACT array 0.05 Arizona, USA