Download Supporting material for Lecture 2

Supporting material for Lecture 2:
Gamma-ray satellites
Cherenkov light telescopes
Apparent and absolute magnitudes
Gamma-Rays: 100 keV - TeV
Satellites: up to 300 GeV
Fermi Large Area
Telescope (LAT)
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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
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
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Spectral overlap with the LAT
(150 keV-30 MeV)
Courtesy: N. Omodei
The AGILE satellite
Launched 23 April 2007
AGILE
SuperAGILE (18-60 keV)
GRID (30 MeV - 50 GeV)
Minicalorimeter
(0.35 - 100 MeV)
Energy > 30 GeV
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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
Huygens’ construction of wave fronts
Cherenkov Telescopes: MAGIC
Major Atmospheric Gamma-ray Imaging Cherenkov Telescope
Camera: 3.5°FoV
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TeV blazar Mkn421 (z = 0.031):
Light curves and spectra
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QuickTime™ and a
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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
Some relevant apparent magnitudes:
Sun
-26.73
Full Moon
-12.6
Venus (at Max brightness) -4.6
Sirius
-1.47
How do we transform magnitudes into fluxes?
Wehrle et al. 1998
Comparison of optical images before and after cosmic ray
correction
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]