Abstract
Exploiting the earth atmosphere as a giant detector for the incoming extraterrestrial fl ux of high energy cosmic rays and cosmic neutrinos, the mission «EUSO-Extreme Universe Space Observatory» is devoted to the exploration of the domain of the highest energy processes occurring in the universe up to its accessible boundaries. The observable is provided by the air nitrogen fl uorescence light emitted in the UV band 300-400 nm by the extensive air showers produced by the cascading processes of the primary cosmic radiation particles interacting with the atmosphere. The EUSO telescope is based on a double Fresnel lens optics (diameter 2.5 m) coupled to a highly pixelized focal surface composed multianode PMTs; the image at the earth surface is detailed at 1 km2 over a total of several hundred thousand of km2. EUSO will fl y on the International Space Station accommodated as external payload of the European Space Agency Columbus module. The mission is scheduled to last 3 years, with the start of operations foreseen for 2007/8. The expectations are of a collection rate of a thousand events/year for cosmic rays at E > 1020 eV together with tens/hundreds of cosmic neutrinos at energy above about 4 ¥ 1019 eV. EUSO is the result of the collaborative effort of several institutions in Europe, Japan and USA and it is conceived within the science program sponsored by various space agencies coordinated by ESA.
Highlights
Cosmic radiation can be considered the «particle channel» complementing the «electromagnetic channel» proper of conventional astronomy.(*) This text is largely derived from contributions made by the author in 2000/2001 to other Workshops and Conferences and from documentation submitted by the EUSO Consortium to the European Space Agency as a part of the EUSO proposal.A classic presentation of the cosmic ray energy spectrum is shown in fig. 1; an unconventional view is given in fig. 2 to illustrate in an anthropomorphic perspective the features conventionally called «knee» and «ankle»
From a Low Earth Orbit (LEO) space platform, the UV fluorescence induced in atmospheric nitrogen by the incoming radiation can be monitored and studied
Other phenomena such as meteors, space debris, lightning, atmospheric flashes, can be observed, while the luminescence coming from the Extensive Air Showers (EAS) produced by the cosmic ray quanta can be disentangled from the general background exploiting its fast timing characteristic feature
Summary
Cosmic radiation can be considered the «particle channel» complementing the «electromagnetic channel» proper of conventional astronomy. A classic presentation of the cosmic ray energy spectrum is shown in fig. 1; an unconventional view (which I borrowed from a colleague of Karlsruhe, where it was first shown at the ceremonial organized in honor of Dr Shatz) is given in fig. 2 to illustrate in an anthropomorphic perspective the features conventionally called «knee» (around 1015 eV) and «ankle» (above 5 ¥ 1018 eV). Today substantial progress has been made in the knowledge of the nature of cosmic rays of the relatively modest energies (up to the «knee» at 1014-1015 eV). On the other hand the cosmic radiation on the higher energy side presents us with the challenge of understanding its origin and its connection with fundamental problems in cosmology and astroparticle physics. EUSO: using high energy cosmic rays and neutrions as messengers from the unknown universe. A direct question arising is: what is the maximum cosmic ray energy, if there is any limit? Addressing the theoretical issue concerning the production and propagation of 1020 eV primary quanta is problematic and involves processes still little known
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