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

TLDR: In this article, the authors 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.

About: This article is published in Astroparticle Physics.The article was published on 2013-04-01 and is currently open access. It has received 148 citations till now. The article focuses on the topics: Nadir & Ultraviolet light.

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Table 1: Parameters of the JEM-EUSO telescope. The values in parenthesis apply at the edge of the FoV, otherwise at the the center of the FoV. The ensquared collection efficiency is the ratio of the number of photons focused within a pixel area to those incident on the entrance aperture of the optics. The ensquared energy is the ratio of photons focused within the area of a pixel to those reaching the FS.

Figure 3: Observational duty cycle η as a function of threshold background level Ithr BG .

Figure 11: Trigger probability as a function of core location with different geometrical and energy cuts: top) E > 3.2 × 1019 eV with θ > 60◦; middle) E > 5.5× 1019 eV and bottom) E > 1020 eV. The last two cases are with no zenith angle cuts.

Table 3: Relative occurrence of clouds over the ISS orbit, taken from the TOVS database for nighttime, are presented as a matrix of cloud-top altitude vs optical depth for all location and only ocean.

Figure 7: Top panel shows the projected tracks on the Earth’s surface for EASs with E = 1020 eV and zenith angles of a) θ = 30◦, b) θ = 60◦ and c) θ = 75◦. The dashed curves indicate the corresponding areas for the FoV of individual PDMs. In the sub-panel, the corresponding area of the plot is represented by solid lines within the entire FoV. Bottom panel shows the image on the FS for the case b). The large squares denotes PMTs. The matrix of pixels are indicated with the integrate counts in discrete scale. The regions enclosed by thick dashed lines in both panels refer to the same PDM.

Figure 15: Exposure in arbitrary unit for different values of maximum acceptable background level.

Frequently asked questions

Q1. What are the contributions in this paper?

In the present work, the authors discuss the particularities of space-based observation and they compute the annual