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

TL;DR

This paper assesses the exposure of the JEM-EUSO space observatory during nadir observations, highlighting its potential to significantly surpass ground-based cosmic ray detectors in annual exposure.

Contribution

It provides a detailed evaluation of the expected annual exposure of JEM-EUSO, considering observational conditions, clouds, and background light effects, which was not comprehensively analyzed before.

Findings

Annual exposure is about ten times higher than ground-based observatories.

Clouds and background light significantly affect observational efficiency.

JEM-EUSO's space-based observation offers a substantial advantage in detecting ultra-high energy cosmic rays.

Abstract

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