La radio détection des rayons cosmiques

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Going up to the highest energy

Thursday 5 April 2007, by Arnaud Bellétoile

Beside the experiment of Codalema itself, researchers of the group are beeing running a campaign of measurements on the south site of the Pierre Auger Observatory in the Argentinian Pampa. This over-sized detector is currently beeing measuring the most energetic part of the cosmic ray spectrum, around 1020 eV. With a covered area of 3000km², it is able to counterbalance the extreme rarity of such energetic cosmic rays (less than one per km² per century). This experiment has been called RAuger, standing for Radio at Auger.

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The team in Argentina

The detector

Thanks to a close collaboration between both Codalema and Auger group, a new prototype of a completely autonomous detector has been designed.

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One device from behind

It results in a group of 3 Pampa-proof elementary devices with their own dipole antenna detector, solar power supply, able to digitized radio signals in the "Codalema way" and to transmit that information using Wifi emitters to a central acquisition system, located in a building miles away.

The central acquisition system can then forward the collected data via the internet to the laboratory, in France.

When an energetic cosmic rays enters the atmosphere, an interaction occurs and a cascade of secondary particules is produced. Those particules will porpagate down to the ground, that’s what is called an extensive air shower.

When one of those shower particles falls upon the detector (a shower can cover an area of several km²), the first thing we want to know is its arrival direction.
If ones wants to determine such an arrival direction, 3 time references at 3 several locations are needed to perform a triangulation.That is why 3 devices were needed each one with an embedded sharp timing system. This system, developped by the Auger group, is based on corrected GPS and offers an accuracy of 0.00000001 second.

Present and futur

The main purpose of this experiment is to compare both systems, the Auger one, which has been known for decades now, and the Codalema one that uses radio detection which is a brand new technique.

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One of our device in the Pampa

Taking advantage of the Auger knowledge means that many questions can be solved about the radiodetection, such as the distance at which an extensive air shower can be seen with radio or the size of the radio signal generated by such energetic particles, etc...

The whole system has been implanted in the Pampa and is currently beeing running, providing information from the other side of the globe to be processed.

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A surprising visitor in the Pampa

Those informations will be helpful and will come in addition to those collected by the Codalema experiment itself to design the next generation of radio detection instrument.