Modeling the Optical Cherenkov Signals by Cosmic Ray Extensive Air Showers Directly Observed from Sub-Orbital and Orbital Altitudes

Abstract

Future experiments based on the observation of Earth's atmosphere from sub-orbital and orbital altitudes plan to include optical Cherenkov cameras to observe extensive air showers produced by high-energy cosmic radiation via its interaction with both the Earth and its atmosphere. As discussed elsewhere [1, 2], particularly relevant is the case of upward-moving showers initiated by astrophysical neutrinos skimming and interacting in the Earth. The Cherenkov cameras, by looking above Earth's limb, can also detect cosmic rays with energies starting from less than a PeV up to the highest energies (tens of EeV). Using a customized computation scheme to determine the expected optical Cherenkov signal from these high-energy cosmic rays, we estimate the sensitivity and event rate for balloon-borne and satellite-based instruments, focusing our analysis on the Extreme Universe Space Observatory aboard a Super Pressure Balloon 2 (EUSO-SPB2) and the Probe of Extreme Multi-Messenger Astrophysics (POEMMA) experiments. We find the expected event rates to be larger than hundreds of events per hour of experimental live time, enabling a promising overall test of the Cherenkov detection technique from sub-orbital and orbital altitudes as well as a guaranteed signal that can be used for understanding the response of the instrument.

Ultra High Energy Cosmic Rays an overview

“…2.11. Though the published measurements of X max [74,75,196] at TA [30] seem to be in tension with this picture, they are compatible with the results of Auger within the current statistical and systematic uncertainties [190][191][192].…”

“…We conclude stating that a complete picture of the ultra high energy universe needs to account for all messengers till the highest energies. The sensitivity required to detect UHE neutrinos and gamma rays, as well as the highest energy tail of CR, is still far from being reached, new technologies are needed and future space observatories, with improved photon detection techniques, allowing the needed statistics, might open a new era in the physics of UHE cosmic radiation [29,30,31].…”

Characterization of atmosphere-skimming cosmic-ray showers in high-altitude experiments

“…The peculiar characteristics of the longitudinal and lateral development of AS showers presented in this work have been shown to influence the properties of optical Cherenkov emission in this type of showers [22], and they are expected to have an important influence on the properties of the radio pulses in the MHz-GHz frequency range as well [32,34]. Detailed modelling of these pulses [21] is crucial for the interpretation of the signals recorded at balloon-borne experiments exploiting the radio technique.…”

“…Limited progress has been done in understanding the influence that the peculiar geometry, the propagation in a rarefied atmosphere, and the significant particle deflection in different magnetic field configurations have on the properties of the showers [20]. These properties will in turn largely determine their emission in radio wavelengths [21], as well as in the optical and UV [22,23]. Some general characteristics of atmosphere-skimming showers were first pointed out in [24] and studied in [25].…”