Pierre Auger Observatory

Observatory

SD Tank of the Pierre Auger Observatory in Malargüe, Mendoza Province near the Andes range

Back view of a tank

The Pierre Auger Observatory is an international cosmic ray observatory designed to detect ultra-high-energy cosmic rays: single sub-atomic particles (protons or atomic nuclei) with energies beyond 10²⁰ eV (about the energy of a tennis ball traveling at 80 km/h). These high energy particles have an estimated arrival rate of just 1 per km² per century, therefore the Auger Observatory has created a detection area the size of Rhode Island — over 3,000 km² (1,200 sq mi) — in order to record a large number of these events. It is located in western Argentina's Mendoza Province, in one of the South American Pampas.

The observatory was named after the French physicist Pierre Victor Auger. The project was proposed by Jim Cronin and Alan Watson in 1992. Today, almost 500 physicists from 55 institutions around the world are collaborating to build the southern site. The 15 participating countries are sharing the $50 million construction budget, each providing a small portion of the total cost.

Overview

The observatory has been taking production-grade data since 2005 and was officially completed in 2008. In 2003, it became the largest ultra-high energy cosmic ray detector in the world. It is located on the vast plain of Pampa Amarilla, near the town of Malargüe in Mendoza Province, Argentina. The basic set-up consists of 1600 water tanks (water Cherenkov Detectors, similar to the Haverah Park experiment) distributed over 3,000 square kilometres (1,200 sq mi), along with four atmospheric fluorescence detectors (similar to the High Resolution Fly's Eye) overseeing the surface array. Work is ongoing on upgrades to the observatory, including:

• three additional fluorescence telescopes, capable of covering higher altitudes (HEAT — High Elevation Auger Telescopes)
• two higher-density nested arrays of surface detectors combined with underground muon counters (AMIGA — Auger Muons and Infill for the Ground Array)
• a prototype radiotelescope array (AERA — Auger Engineering Radio Array) for detecting radioemission from the shower cascade, in the frequency range 30-80 MHz
• R&D on detecting microwave emission from shower electrons (frequencies around 4 GHz)

The Pierre Auger Observatory is unique in that it is the first experiment that combines both ground and fluorescence detectors at the same site thus allowing cross-calibration and reduction of systematic effects that may be peculiar to each technique. The Cherenkov detectors use 3 large photomultiplier tubes to detect the Cherenkov radiation produced by high-energy particles passing through water in the tank. The time of arrival of high-energy particles from the same shower at several tanks is used to calculate the direction of travel of the original particle. The fluorescence detectors are used to track the particle shower's glow on cloudless moonless nights, as it descends through the atmosphere.

The Pierre Auger Collaboration has made available (for outreach purposes) 1% of the full ground array data set. This data can be explored at the Public Event Display web site.

In November 2007, it was announced that the observatory had found a correlation between the 27 highest energy events and nearby active galactic nuclei (AGN). This would suggest that these events are triggered by protons that were emitted by objects correlated with the AGN distribution of matter. Acceleration by the large magnetic fields associated with the massive central black holes that form the AGNs is one possibility.

Postage stamps

Argentina issued 100,000 postage stamps honouring the observatory on 14 July 2007. The stamp shows a surface detector tank in the foreground, a building of fluorescence detectors in the background, and the expression "10²⁰ eV" in large lettering.

Further reading

• November 2007 AGN Press Release
• Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects: Science 2007 (subscription required). Arxiv preprint (free but not official).
• Let It Rain Symmetry February 2005

External links

• Official website
• Public Event Display
• Southern site website (Spanish and English)
• COSMUS – visuals for the PAO: includes movies, animated 3d models of cosmic ray showers over the Malargues site, and stereo photographs.
• ASPERA European astroparticle physics network
• Astroparticle.org – European astroparticle physics portal
• Detecting Cosmic Rays: The Auger Observatory and Frontier Science – Interview with Angela Olinto (video)