FermiLAT To high energies The violent universe Gamma

Fermi-LAT: To high energies

The violent universe • • • Gamma ray bursts Active galactic nuclei Pulsars Supernova remnants Gamma ray background (particle annihilation) • All produce high energy radiation 2

Earlier missions • OSO-3 • COS-B • • 1967 (> 50 Me. V) 1975 – 1982 (ESA’s first > 30 Me. V) Vela! (secret programme in 1960 s, data published 1973) Compton GRO 1991 – 2000 (17 tons) Beppo. SAX 1996 – 2003 INTEGRAL 2002 – present 3

INTEGRAL 4

• • • 5 m x 2. 8 m x 3. 2 m ESA – Russia collaboration X-rays and Gamma rays IBIS: 15 ke. V – 10 Me. V (imager, 12 arcmin) SPI: 20 ke. V – 8 Me. V (spectrometer, 2 ke. V) JEM-X X-rays 3 – 35 ke. V. 5

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The next step: Fermi 7

Fermi • NASA+ • Launched 2008 • Main instrument: LAT – – – FOV: 20% of sky 1 arcmin resolution (bright sources) 30 Me. V – 300 Ge. V (first with sensitivity > 10 Ge. V) High time resolution Filters, since 10 -5 – 10 -6 of hits are gamma rays 8

Very high energy gamma rays • Extremely high -> CTA • How to detect them? 9

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• A gamma ray enters the LAT. It first passes through the Anticoincidence Detector without producing a signal. • The gamma ray interacts in one of 16 thin tungsten sheets. This interaction converts the gamma ray into an electron and a positron via pair production (governed by Einstein’s equation E=mc 2). • The Tracker uses silicon strips to measure the paths of the electron and positron, allowing the LAT to determine the arrival direction of the gamma ray. • The electron and positron enter the Calorimeter, which measures the energies of the particles, and therefore the energy of the original gamma ray. 11

• Unwanted cosmic-ray particles produce a signal in the Anticoincidence Detector, which tells the Data Acquisition System to reject the signal. The Anticoincidence Detector rejects 99. 97% of unwanted signals produced by cosmic rays that enter the LAT. • Software in the LAT Data Acquisition System also rejects, based on arrival direction, unwanted gamma rays that originate in Earth’s atmosphere. 12

Different detectors • • Gamma-ray X-ray UV Visible IR Microwave Radio – You have previously had a look at Euclid and CCDs 13

Fermi images 14

Blasarer 15

Pulsarer 16

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