Radio detection of Cosmic Ray Air Showers

1
Radio detection of Cosmic Ray Air Showers
The CODALEMA experiment

• A. Bellétoile
• for CODALEMA collaboration
• SUBATECH - Université de Nantes - EMN - IN2P3
• Observatoire de Paris-Meudon, Station de Nançay -
  INSU
• LAL - IN2P3
• ESEO
• LPSC Grenoble - IN2P3

2
Summary

• Origin characteristics of the signal
• Experimental device
• First results evidences for a radio signal
  associated with CR Air Shower

3
Origin characteristics of the radio signal

• Radio detection interests
• Shower direction
• Triangulation
• Primary particle energy
• Amplitude of the electric field
• Nature
• Longitudinal profile of the shower (Xmax)

• Production mechanisms
• Negative charge excess in the shower
• 10 e- / e
• Charge deflection in the Earth s magnetic field
• Probably the main contribution
• Detection at large distance is possible

4
Theoretical signal

• Vertical shower _at_ E  1017 eV and small impact
  parameter
•  H. R. Allan (1971)
• ?pk150 ?V/m
• FWHM duration 8 ns
•  Broad-band antennas needed
•  1-100 MHz

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The Codalema Experiment

• Decametric Array of the radio observatory of
  Nançay
• 144 log periodic antennas
• Bandwidth 1-100 MHz
• High sensitivity

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First steptransient detection
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Test of triangulation

• Triangulation
• Minimum 3 tagged antennas
• Plane wave front hypothesis

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Particle detectors as trigger

• 4 particle detectors in coincidence
• Active area 7000 m2
• Counting rate 0.7 evt/min
• Energy threshold1.1015 eV
• No particle detectors pollution
• No correlation between PM and antenna signal
  amplitudes

9
Time correlation

• ? 3 antennas flagged
• Time correlation distribution
• Fortuitous events
• Flat distribution
• Candidates
• Sharp peak (lt 100ns)

10
Arrival direction correlation

• Good events
• Angular difference 2.5º RMS
• 0.3 evt / day

• Rough estimation of the energy threshold
• gt 5.1016 eV

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Field topologies (in progress)

• Variable antenna multiplicity
• Field amplitudes measured
• From 250 ?V/m to 1.2 mV/m in 40 - 70 MHz
• Extension of the field
• gt 100 m
• more antennas needed

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Conclusion

• Evidence for radio signal associated with CR Air
  Showers
• Operating instrument
• Codalema program
• Additionnal antennas and particle detectors
• long distance radio signal behavior
• core position
• shower energy
• Stand-alone antennas associated with giant
  detector

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Transient rate with one antenna as trigger
(stand-alone mode)

• Knowledge of the radio background
• Atmospheric conditions
• Human activity
• Solar activity
• Low rate
• lt1Hz
• 100 duty cycle

14
Simulation of the signal _at_ E1020 eV

• Vertical shower
• With charge excess only
• b0.5 km Epeak1500 ?V/m
• FWHM duration100 ns
• b1km Epeak200 ?V/m
• FWHM duration 275 ns
• broad-band antennas needed
• 1-100 MHz
• plus
• geomagnetic field contribution expected 10 times
  greater
• inclined shower configuration more favourable

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Interaction Scintillators/Antennas
No signs of pollution
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Résultats préliminaires
Direction darrivées scintillateurs
Taux de trigger (particules) Pour 4 stations
0.7 evt/mn gt seuil Eincident 1015 eV
limite angulaire 0 lt q lt60 pas de limite en
F