1. Some Results of the Codalema
Experiment at Nançay
Ahmed Rebai
Subatech Laboratory Nantes
JED le Mans 30 June 2011
• Introduction
• North-South Asymmetry
• Energy Calibration
• Reconstruction of the radio wave emission center

2. Motivations
Auger data 2008
Many unanserewed questions about cosmic rays with
energies in the range of joule (~ 1019 eV )
Nature of those particles ?
Astrophysical Sources ?
A limit in their energies ?
Radio-detection as a complementary detection
technique ?
Surface
Duty Cycle
Cost, simplicity
Angular resolution , Energetic resolution ?
Nature of the cosmic rays ?
Since 2003 installation of CODALEMA
experiment at Nançay: as demonstration of
the feasibility and potential of this method

3. Motivations
Cosmic rays spectrum
CODALEMA energy
range
Energy Threshold : 5.1015 eV
Trigger Rate : 1 evt/ 7 mn
Analysis Threshold : 5.1016 eV
Counting rate : 1 good evt/3 days
Detection surface : 0.25 km2

4. CODALEMA Experiment@Nançay
Codalema actual setup Array of short antennas
-21 dipole antennas E-W
- 3 dipole antennas N-S
Decametric array
18 groups of 8 log-periodic
phased antennas
Scintillator array
17 scintillator
=>Experiment Trigger
=> Energy Estimator

5. Radio Emission
10% e-,e+
e-/e+ deflection under the geomagnectic field
effect  dipole emission, transverse
current, synchrotron radiation
+ - Time variation of the negatif charge excess
monopole emission
Time variation of the charged particles
number
Radio Signal
Frequency ~ 100 MHz
Amplitude ~ 100 µV.m-1
Duration ~ 1 ns – 100 ns
Xmax
Maximum shower
development Nmax
maximum particles
number

6. Detection method
Numeric filter in the 23-83
MHz band
AM
FM
Amplitude [V]
+ Corrections : time delay,
Time [s] attenuation, antennas gain
1 event = 2 physical quantities / antenna ( amplitude Vi , time ti , … )

7. Arrivals direction reconstruction
•Hypothesis: plane wave front Ux.x+Uy.y+Uz.z + cte =0
•Maximum amplitude time ti on antennas
IG11 ID32 IA1
σ = 1.6°
ITrigger ID98
Arrival direction
Θ : Zenithal angle
Φ : Azimuthal angle

8. North
Emission mechanism
Detection threshold correlated
with arrivals directions
 Geomagnetic Effect
B
 Radio Signal Amplitude ~ |VxB|E-W
South D.Ardouin & al Astro.ph 31 2009
Polarization E-O CODALEMA Model
|VxB|E-W minimum Zenith |VxB|E-W maximum (also SELFAS2, ReAIRES)
B
confirmed at RAuger@Auger
θ=27°
North Argentina (magnetic field
South inversed in the southern
hemisphere)

9. Lateral Profil Distribution
Radio signal lateral profil in the ground
=> Allan formula : E = E0.exp(-d/d0)
E0 on the shower axis
d0 distance of the shower decay
(X0, Y0) shower core
1 event = (E0, d0, X0, Y0)
 Use of E0 as an energy estimator of the primary particle

10. Energy Correlation
Ep estimated with the CIC
method (Constant intensity Cut)
ΔEp/Ep ~ 30 %
ΔE0/E0 < 10 %
E0 ~ Epα avec α ~ 1.0 
linear dependency
Calibration depends on :
E0 errors
Ep errors
E0 =a Ep + b  Radio calibration Egerbe =(1/a)*E0 – b/a

11. Radius of Curvature
Approximation 0  a plane
wave front
Approximation 1 
Non planar wave front +
Emission center in a distance R
Time [s]

12. Radius of Curvature
Systematic gap / planewave front  Non planar
wavefront
U x  x  U y  y  U z  z  (U x  x fta  U y  y fta  U z z fta )  0
σt= 10 ns U x  x  U y  y  (U x  x fta  U y  y fta )
d
U x U y Uz
2 2 2
Data
tth  d
c
First tagged antenna t0 .
tth – t0 = Expected delay
tps – t0 = Experimental delay
Simulation
 Example of a simulation (spherical wave front):
 Delay decrease  R increase  Far emission center 
planewave front
 Delay increase  R decrease  Near emission center 
Curved front

13. Radius of curvature Estimation : Fitting of the
waveplan front gap
•Hypothesis = parabolic gap

c. t i
max
t i
pred
  a 
 1  r r2 r r2 r r
   
 2.R . xi  xc  yi  yc  zi  zc
 
2
 c
5 free parameter model :
σ = 3m
Shower Core coordinate xc, yc et zc
Radius of curvature Rc  Emission center
4 km
? Radius of Curvature distribution
maximum ~ 4 km …
… But interpretations difficulties
(Very large Radius observed)

14. Towards a direct shower energy estimator
z
radio Hypothesis : Emission Center = Xmax
X max
f Linsley ( Rc . cos( ))
X max 
cos( )
θ Rc
sol
Greisen Model  Shower of only e-/e+
Xmax = X0ln (Ep/E0)  Ep
X0 = 36.7 g.cm-2
E0 = 83 MeV

15. Towards a autonomous radiodetection array : CODALEMA3
60 automous stations to be installed at Nançay during 2011
Array with 1 km2 of surface
Exploration in continuity of the Codalema physic
programme

16. Conclusions
Faisability of radiodedection with CODALEMA 2:
 Detection of the radio signal induced by the shower
developpement
 Emission mechanism : geomagnetic effect
 Energie Correlation
New analysis method : Rc
Exploration of CODALEMA 3 (autonomous station)
Thank you