An evaluation of the exposure in nadir observation of the JEM-EUSO mission

Abstract

We evaluate the exposure during nadir observations with JEM-EUSO, the Extreme Universe Space Obser-\ud vatory, on-board the Japanese Experiment Module of the International Space Station. Designed as a mis-\ud sion to explore the extreme energy Universe from space, JEM-EUSO will monitor the Earth’s nighttime\ud atmosphere to record the ultraviolet light from tracks generated by extensive air showers initiated by\ud ultra-high energy cosmic rays. In the present work, we discuss the particularities of space-based obser-\ud vation and we compute the annual exposure in nadir observation. The results are based on studies of the\ud expected trigger aperture and observational duty cycle, as well as, on the investigations of the effects of\ud clouds and different types of background light. We show that the annual exposure is about one order of\ud magnitude higher than those of the presently operating ground-based observatories

Preliminary results from the first EUSO-Balloon flight

“…estimate the exposure curve as a function of energy [15]. Measurements have been performed in the past by BaBy [16], NIGHTGLOW [17] and Sakaki et al [18], however, EUSO-Balloon uses an optical refractive system with very fine spatial and temporal resolutions which allows a much better determination of the space and time variations of the UV intensity.…”

Calibration of photo sensors for the space-based cosmic ray telescope JEM-EUSO

“…Typically an EAS signature has a lifetime of roughly 200 µs. The maximum number of photons at the aperture per time bin (2.5 µs) is according to simulations in the order of a few hundred photons [1]. Therefore, the used detectors must be sensitive to single photons.…”

“…The first and the third lense are focusing, the second lens is a diffusing lense. The optics are made to correct for aberrations and have a focal point of roughly 2 mm in diameter [1].…”

A Cockcroft-Walton High-Voltage Power Supply for the EUSO Instruments

“…The Japanese Experiment Module-Extreme Universe Space Observatory (JEM-EUSO) telescope is intended to measure the highest energy cosmic rays (so called Ultra-High Energy Cosmic rays (UHECR)) by monitoring the Earth's atmosphere from the International Space Station (ISS) [1]. The advantage of this approach is the huge geometrical factor, as an area with a radius of about 200 km would be monitored.…”