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```									Atmospheric shower simulation
studies with CORSIKA

ARISTOTLE UNIVERSITY OF THESSALONIKI

Physics Department

Atreidis George
High energy gamma ray astronomy at 100 GeV - 100 TeV

   High energy gamma rays photons.

   Coming from a distant source
outside the Earth.

   Energies beyond those achievable

   When a VHE gamma-ray enters the Earth's atmosphere, it generates an
atmospheric shower.

 secondary charged particles             Cherenkov light
Detection – Air showers
interaction

atmospheric
shower

air shower
telescopes (AST)

Cherenkov
photons
Atmospheric shower simulation with Corsika

   Primary particle – gamma ray photon.
   Three sets of showers. Every set consists of 10 showers.
   The primary particle energy is.

First set           10 TeV
Second set           40 TeV
Third set           70 TeV

   Zenith angle  20 deg.
   Azimuth angle  from -180 to 180 deg.
   Observation level  110m above sea level.
   The results are average values for each set of shower.
Coordinate system in Corsika

   The coordinates in CORSIKA are defined with respect to a Cartesian
coordinate system.

 The positive x-axis points to the
magnetic North.

 The positive y-axis points to
the West.

 The z axis points upwards.

 The origin is located at sea level.
Θ  Zenith angle.

Φ  Azimuth angle.
Gamma particles distribution

Gamma particles distribution

2,00E+04

1,60E+04
No of gamma particles

1,20E+04

8,00E+03

4,00E+03

0,00E+00
0      200           400            600      800     1000
Depth (g/cm**2)

10 TeV

Starting point.
The top of the atmosphere.                                   Shower maximum
at a depth of 420 g/cm2.                    Observation level.
110 m above sea level.
Gamma particles distribution
Gamma particles distribution

1,20E+05
No of gamma particles

8,00E+04

4,00E+04

0,00E+00
0      200           400            600            800   1000
Depth (g/cm**2)

10 TeV   40 TeV     70 TeV

 Big primary energy  more gamma particles.

 Shower maximum  goes deeper.
Positrons distribution

Positrons distribution

20000

16000
No of positrons

12000

8000

4000

0
0       200          400            600            800   1000
Depth (g/cm**2)

10 TeV     40 TeV    70 TeV

 Big primary energy  more positrons.

 Shower maximum  goes deeper.
Electrons distribution

Electrons distribution

25000

20000
No of electrons

15000

10000

5000

0
0        200       400            600            800   1000
Depth (g/cm**2)

10 TeV   40 TeV     70 TeV

 Big primary energy  more electrons.

 Shower maximum  goes deeper.
Lateral electron density
at observation level

Lateral electron density
for the three
primary energies
8,00E-05
the density is
Electron density

4,00E-05

2,00E-05

0,00E+00
0    500   1000    1500    2000    2500   3000      3500   4000   4500   5000
Distance from core (cm)

10 TeV       40 TeV       70 TeV

at a distance of 14 m from the core
Shower energy distribution
Longitudinal energy distribution

1,25E+04

1,00E+04
Energy (GeV)

7,50E+03

5,00E+03

2,50E+03

0,00E+00
0     200        400           600        800   1000
Depth g/cm**2

10 TeV

 Continuing reduction in the shower energy.

 Energy loss  energy deposit into air.
Energy deposit into air

Energy deposit (primary particle 70 TeV)

2000
ionization
energy deposit
1600
cut energy for
Energy (GeV)

gamma particles                                    cut energy for
1200
(0.15GeV)                                     electrons – positrons
(0.15 GeV)
800

400

0
0            200         400            600               800        1000
Depth (g/cm**2)

gammas     e+-ioniz     e+-cut
Number of charged particles at observation level
Observation level 110 m above sea level

Number of electrons - positrons at observation level

300

250
Ne>Np

200

150

100

50

0
1                             2                             3

Energy (TeV)   No of electrons    No of positrons

More primary energy  more particles at observation level.
Locations of Cherenkov detectors in the simulation

 Number of Cherenkov detectors in x direction10
 Number of Cherenkov detectors in y direction 8
 Distance of detectors in x direction1200 cm
 Distance of detectors in y direction 1500 cm

 Length of the detector in x direction 80 cm

 Length of the detector in y direction 50 cm.
Production of Cherenkov photons per 20g/cm2

Production of Cherenkov photons per 20 g/cm**2)

1,60E+08

More Cherenkov photons
No of Cherenkov photons

1,20E+08                                         at the shower maximum.

8,00E+07

4,00E+07

0,00E+00
0        200        400            600          800    1000      1200
Depth (g/cm**2)

Primary particle 70 TeV

Starting point.                                                                                     Observation level.
The top of the atmosphere.                                                                              110 m above sea level.
Total production of Cherenkov photons

Cherenkov photons distribution

3,00E+09
No of Cherenkov photons

2,00E+09

observation
level
1,00E+09

0,00E+00
0       200       400        600          800   1000   1200
Depth (g/cm**2)

10 TeV   40 TeV   70 TeV

 The Cherenkov photons generated at all depths reach the observation level.

 At great depths the number of Cherenkov photons created are small, so the total
number tends to become stable.
Increase Cherenkov photons with energy
• Number of Cherenkov photons arriving at the observation level.
Total Cherenkov photons - energy

3,00E+09
No of Cherenkov photons

2,00E+09

1,00E+09

0,00E+00
0   10       20      30       40         50   60   70   80
Primary particle energy

Cherenkov

 The increase in the Cherenkov photons in connection with the energy
of the primary particle is almost linear.
Experiments in High Energy Gamma Ray Astronomy
Telescope arrays for the detection of Cherenkov light

     H.E.S.S. experiment
 Located in Namibia, near the Gamsberg mountain.
 Energies from 100GeV to 100TeV.

    MAGIC experiment
 Located in La Palma, one of the Canarian islands.
 Energies >100GeV.

 Mirror surface 236m2.

     VERITAS experiment
 Located in southern Arizona of the USA.

 Energies from 50GeV to 50TeV.

 An array of four 12m optical reflectors.
New Experiment - CTA

    Location
 Not yet determined.

    Three telescope types
 Four 24 m telescopes with 5o field-of-view.
 23 telescopes of 12 m diameter with 8o field-of-view.

 32 telescopes of 7 m diameter with a 10o field-of-view.

     Telescopes distribution
 The telescopes are distributed over 3 km2 on the ground.

 The effective collection area of the array is considerably larger than this at
energies beyond 10 TeV.

       Cost

Array layout has a nominal construction cost of 80 M€ and meets the
main design goals of CTA.
Conclusions

The high-energy range above 10TeV

For very high primary particle energy ~100TeV the maximum of the shower
goes deeper and the Cherenkov light reaches its ultimate intensity at about
800 g/cm2 or ~2 km in altitude.
So

The observation level                                   The detectors should be
should be lower.                                       extended more widely.

Two implementation options

either a large number                                or a smaller number
of small telescopes                                 of larger telescopes