Earth is constantly being bombarded by high-energy cosmic rays. While it’s thought cosmic rays with energies up to 1015 eV originate from objects in our own Galaxy, such as colliding supernovae, the origin of ultra-high-energy cosmic rays beyond 5.1019 eV remains a mystery and one of the great challenges facing astrophysics. Ultra-high-energy cosmic particles are protons, nuclei, photons and neutrinos, or new particles with energies in the range of 1018 eV up to tens of 1020 eV, in other words to the very end of the known spectrum. At such ultra-high energies, radiation is generated in the most extreme conditions in the Universe, beyond our current understanding and possibly involving a new kind of physics and astrophysics. These extreme energy cosmic rays (EECR) are very rare, occurring at a rate of no more than one per square kilometre per century. Only 50 such events have been detected by ground telescopes over the last 30 years, no convincing possible source for them has yet been identified and we know nothing about the nature of the particles emitted.
EUSO-Balloon is a prototype of future UV telescopes designed to detect ultra-high-energy cosmic rays from satellites or the International Space Station (ISS), like the JEM-EUSO joint project between 2012 and 2014. JEM-EUSO produced a complete subassembly of the focal plane (composed of 36 multi-anode 64-channel photomultipliers, 36 ASICs, an FPGA board, a telemetry module and other equipment) constituting a science suite intended to validate a range of envisioned technologies and, more broadly, the complete detection system of a future space mission, from the detector to processing electronics, the trigger process for recording of events, electronic and mechanical systems, and data storage.
The EUSO-Balloon mission, with funding for its French partners provided by CNES, conducted a first technological flight of the instrument on a CNES stratospheric balloon during the night of 24-25 August 2014. The flight was a great success, validating the measurement concept, determination of the ground UV signal (which will constitute background noise when observing air showers) and even detection of simulated events (xenon flashes and a laser fired across the field of view more than 30 km below the gondola).
Intensity map of the UV background in photons m-2sr-1ns-1 with a logarithmic scale. Bright zones with high intensity are from artificial light in Timmins and the surrounding area, mines and airport. Red and blue zones indicate cloud cover.
Picture of an event simulated by the helicopter. Signals from the flasher are on the left.
After the success of this flight, EUSO-Balloon is now aiming to detect UV radiation from a giant air shower seen from the sky for the first time. This milestone should be achieved on the second long-duration flight from New Zealand in spring 2017, with a NASA superpressure balloon (SPB).