Supporting material for Lecture 2:

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 gt 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
17 m
17 m
9
(No Transcript)
10
TeV blazar Mkn421 (z 0.031) Light curves and
spectra
11
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
12
Some relevant apparent magnitudes Sun
-26.73 Full Moon -12.6 Venus (at Max
brightness) -4.6 Sirius -1.47
13
How do we transform magnitudes into fluxes?
Wehrle et al. 1998
14
Comparison of optical images before and after
cosmic ray correction
15
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