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Supporting material for Lecture 2: Gamma-ray satellites Cherenkov light telescopes

This supporting lecture material covers gamma-ray satellites, Cherenkov light telescopes, apparent and absolute magnitudes, and the interactions of gamma-rays with matter. Discusses Fermi Large Area Telescope, detection mechanisms, and the AGILE satellite. Explains air showers and current TeV telescopes.

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Supporting material for Lecture 2: Gamma-ray satellites Cherenkov light telescopes

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  1. Supporting material for Lecture 2: Gamma-ray satellites Cherenkov light telescopes Apparent and absolute magnitudes

  2. Gamma-Rays: 100 keV - TeV Satellites: up to 300 GeV Fermi Large Area Telescope (LAT) Gamma-rays need solid state detectors: Interaction of gamma-rays with matter converts the photon into an electron and positron pair. The path of the pair in the silicon strips allows arrival direction reconstruction. Their interaction with the calorimeter allows photon energy reconstruction

  3. The Fermi GST mission: 11 June 2008 LAT Glast Burst Monitor Energy Range: 10 keV - 30 MeV • 12 Sodium Iodide (NaI) Scintillation detectors • Burst trigger • Coverage of the typical GRB spectrum (10 keV 1 MeV) • 2 Bismuth Germanate (BGO) Scintillation detectors • Spectral overlap with the LAT (150 keV-30 MeV) Courtesy: N. Omodei

  4. The AGILE satellite Launched 23 April 2007

  5. AGILE SuperAGILE (18-60 keV) GRID (30 MeV - 50 GeV) Minicalorimeter (0.35 - 100 MeV)

  6. Energy > 30 GeV Gamma-rays interacting in the atmosphere create what is called an air shower. Electron-positron pairs Travel in the atmosphere With a velocity LARGER than The velocity of light IN THE ATMOSPHERE, and produce Cherenkov light. This is Optical (blue) light, that is Detected by TeV telescopes. Current generation: HESS, MAGIC, VERITAS, Cangaroo

  7. Huygens’ construction of wave fronts

  8. Cherenkov Telescopes: MAGICMajor Atmospheric Gamma-ray Imaging Cherenkov Telescope Camera: 3.5°FoV 17 m 17 m

  9. TeV blazar Mkn421 (z = 0.031): Light curves and spectra

  10. magnitude refers to the logarithmic measure of the brightness of an object, measured in a specific wavelength or passband, usually in optical or near-infrared wavelengths. The larger the magnitude, the lower the flux. Vega has m = 0 Apparent magnitude (m), the apparent brightness of an object. Absolute magnitude (M), which measures the luminosity of an object (or reflected light for non-luminous objects like asteroids); it is the object's apparent magnitude as seen from a certain location. For stars it is 10 parsecs (32.6 light years). The apparent magnitude can be measured directly; the absolute magnitude can be derived from the apparent magnitude and distance using the distance modulus:  = m - M

  11. Some relevant apparent magnitudes: Sun -26.73 Full Moon -12.6 Venus (at Max brightness) -4.6 Sirius -1.47

  12. How do we transform magnitudes into fluxes? Wehrle et al. 1998

  13. Comparison of optical images before and after cosmic ray correction

  14. Suggestion for an excellent textbook: Malcolm Longair High Energy Astrophysics Cambridge University Press, 1981 [my edition dates to 1981, but there are more recent ones]

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