Abstract
The origin and nature of Ultra-High Energy Cosmic Rays (UHECRs) remain unsolved in contemporary astroparticle physics. To give an answer to these questions is rather challenging because of the extremely low flux of a few per km2 per century at extreme energies such as E > 5 × 1019 eV. The objective of the JEM-EUSO program, Extreme Universe Space Observatory, is the realization of a space mission devoted to scientific research of cosmic rays of highest energies. Its super-wide-field telescope will look down from space onto the night sky to detect UV photons emitted from air showers generated by UHECRs in the atmosphere. The JEM-EUSO program includes different missions using fluorescence detectors to make a proof-of-principle of the UHECR observation from space and to raise the technological level of the instrumentation to be employed in a space mission. EUSO-TA, installed at the Telescope Array site in Utah in 2013, is in operation. It has already detected 9 UHECRs in coincidence with Telescope Array fluorescence detector at Black Rock Mesa. EUSO-Balloon flew on board a stratospheric balloon in August 2014. It measured the UV intensity on forests, lakesandthecityofTimminsaswellasprovedtheobservationofUHECR-likeeventsbyshootinglasertracks. EUSO-SPB was launched on board a super pressure balloon on April 25th and flew for 12 days. It proved the functionality of all the subsystems of the telescope on a typical duration of a balloon flight; observed the UV emission on oceans and has a self-trigger system to observe UHECRs with energy E > 3×1018 eV. TUS, the Russian mission on board the Lomonosov satellite in orbit since April 28th 2016, is now included in the JEMEUSO program and has detected so far in the UHECR trigger-mode a few interesting signals. Mini-EUSO is in its final phase of integration in Italy, where several performance tests are being held. Mini-EUSO will be installed inside the International Space Station (ISS) in 2019. The main results obtained so far by such missions are summarized and put in prospect of future space detectors such as K-EUSO and POEMMA.
Highlights
The origin and nature of Ultra-High Energy Cosmic Rays (UHECRs) remain unsolved in contemporary astroparticle physics [1]
Different missions from ground, stratospheric balloon and from space have been developed within the JEM-EUSO program to address relevant key aspects in view of a main mission, such as K-EUSO and POEMMA: a) raise the Technological Readiness Level (TRL) of the different components of the JEM-EUSO detector; b) prove the capability of the JEM-EUSO approach to detect UHECRs from space; c) verify the quality of the reconstruction of Extensive Air Showers (EAS) parameters; d) define methodologies to evaluate the instantaneous exposure of the instrument in different atmospheric and observational conditions
The capability of the JEM-EUSO approach to detect UHECR from space was checked by means of EUSOTA and EUSO-SPB in Utah, as well as EUSO-Balloon in space
Summary
The origin and nature of Ultra-High Energy Cosmic Rays (UHECRs) remain unsolved in contemporary astroparticle physics [1]. The typical time fit of a laser event and the direction reconstruction are shown in Fig. 5 after requiring basic quality cuts: a) a set of events of same energy (15 mJ, equivalent to ∼1020 eV EAS); b) a track lasting at least 4 GTUs. It is important to remember that the read-out period of 2.5 μ is optimised for JEM-EUSO, which is expected to detect EAS at ∼400 km distance, instead of ∼35 km as in case of EUSO-Balloon.
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