Astroparticules-Théorie
Radio-electric fields from cosmic-ray
air showers at large impact
parameters
La composante électron-positon de grande énergie dans une gerbe atmosphérique de rayon
cosmique crée un champ électrique radio-fréquences transitoire. Il est utile pour choisir les
caractéristiques du dispositif de détection radio d’avoir une idée des valeurs des impulsions
radioélectriques ainsi que de leur forme et de leur échelle de durée. Un modèle simplifié utilisable à
grand paramètre d’impact est proposé pour l’estimation de ce champ radioélectrique.
High-energy electrons and positrons in cosmic
ray air showers generate transient electric
fields in the radio frequency domain. Estimates
of pulse magnitudes, together with their time
scales and behaviors are useful ingredients for
the design of a radio-detection experiment.
For a very large scale experiment it seems
unrealistic to expect a sampling of the air
shower electric field on a scale much smaller
than a kilometre. This defines the typical
impact distance at which electric field
estimates are needed. At such distances, a
simple model of the shower can be used to
investigate various aspects of air shower
electric field phenomenology.
The formulation of this model is thoroughly
discussed in [1]. A preliminary report on this
work was given at the 30th International
Cosmic-Ray Conference [2].
i.
Electric
field
estimates
Several mechanisms of charge separation in
the shower may lead to a radio electric field
component. Here the so-called transverse
current component is singled out. At large
impact parameter b, the electric field for this
component received at time t at observation
point A reads
E(t,A)=4(ct’)2(Nee(t’)+ t’ N’ee(t’)) J /b4
where Nee is the number of electrons and
positrons in the shower at emission time
t’=-(b/c)2/(2t),
and J is in proportion of the drift velocity