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

Auger data 2008

Many unanserewed questions about cosmic rays with

energies in the range of joule (~ 1019 eV )

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

Nature of those particles ?

Astrophysical Sources ?

A limit in their energies ?

Motivations

CODALEMA energy

range

Motivations

Cosmic rays spectrum

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

Codalema actual setup

-21 dipole antennas E-W

- 3 dipole antennas N-S

Scintillator array

17 scintillator

=>Experiment Trigger

=> Energy Estimator

Array of short antennas

18 groups of 8 log-periodic

phased antennas

Decametric array

CODALEMA Experiment@Nançay

10% e-,e+

Xmax

Maximum shower

development Nmax

maximum particles

number

Radio Emission

-+

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

Frequency ~ 100 MHz

Amplitude ~ 100 µV.m-1

Duration ~ 1 ns – 100 ns

Radio Signal

Detection methodNumeric filter in the 23-83

MHz band

1 event = 2 physical quantities / antenna ( amplitude Vi , time ti , … )

+ Corrections : time delay,

attenuation, antennas gainTime [s]

Am

plit

ude [V

]

FMAM

ITrigger

IG11

ID98

ID32 IA1

Arrivals direction reconstruction

•Hypothesis: plane wave front Ux.x+Uy.y+Uz.z + cte =0

•Maximum amplitude time ti on antennas

Arrival direction

Θ : Zenithal angle

Φ : Azimuthal angle

σ = 1.6°

CODALEMA Model

(also SELFAS2, ReAIRES)

Emission mechanism

Polarization E-O

North

confirmed at RAuger@Auger

Argentina (magnetic field

inversed in the southern

hemisphere)

D.Ardouin & al Astro.ph 31 2009

NorthSouth

Zenith

B

θ=27°

|VxB|E-W minimum |VxB|E-W maximum

B

Detection threshold correlated

with arrivals directions

Geomagnetic Effect

Radio Signal Amplitude ~ |VxB|E-W

South

Radio signal lateral profil in the ground

=> Allan formula : E = E0.exp(-d/d0)

Use of E0 as an energy estimator of the primary particle

E0 on the shower axis

d0 distance of the shower decay

(X0, Y0) shower core

1 event = (E0, d0, X0, Y0)

Lateral Profil Distribution

Energy Correlation

E0 =a Ep + b Radio calibration Egerbe =(1/a)*E0 – b/a

Calibration depends on :

E0 errors

Ep errors

Ep estimated with the CIC

method (Constant intensity Cut)

ΔEp/Ep ~ 30 %

ΔE0/E0 < 10 %

E0 ~ Epα avec α ~ 1.0

linear dependency

Radius of Curvature

Approximation 0 a plane wave front

Approximation 1 Non planar wave front +

Emission center in a distance R

Time [s]

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

cdt

UUU

yUxUyUxUd

zUyUxUzUyUxU

th

zyx

ftayftaxyx

ftazftayftaxzyx

222

)(

0)(

First tagged antenna t0 .

tth – t0 = Expected delay

tps – t0 = Experimental delay

Simulation

Data

Systematic gap / planewave front Non planar

wavefront

Radius of Curvature

σt= 10 ns

Radius of curvature Estimation : Fitting of the

waveplan front gap•Hypothesis = parabolic gap

5 free parameter model :

Shower Core coordinate xc, yc et zc

Radius of curvature Rc Emission center

Radius of Curvature distribution

maximum ~ 4 km …

… But interpretations difficulties

(Very large Radius observed)

222max ..2

1. r

c

r

i

r

c

r

i

r

c

r

i

c

pred

ii zzyyxxR

attc

?

4 km

σ = 3m

Towards a direct shower energy estimator

Greisen Model Shower of only e-/e+

Xmax = X0ln (Ep/E0) Ep

X0 = 36.7 g.cm-2

E0 = 83 MeV

θ Rc

sol

radioX maxHypothesis : Emission Center = Xmax

)cos(

))cos(.(max

c

Linsley RfX

z

60 automous stations to be installed at Nançay during 2011

Array with 1 km2 of surface

Exploration in continuity of the Codalema physic

programme

Towards a autonomous radiodetection array : CODALEMA3

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