Prospects of detecting a large-scale anisotropy of ultra-high-energy cosmic rays from a nearby source with the K-EUSO orbital telescope

TL;DR

This paper assesses the potential of the K-EUSO orbital telescope to detect large-scale anisotropy in ultra-high-energy cosmic rays from nearby sources, using simulations to estimate detection confidence levels.

Contribution

It provides the first detailed simulation-based estimate of K-EUSO's ability to detect anisotropy from specific nearby sources of UHECRs, considering realistic event counts and source fractions.

Findings

Detection of large-scale anisotropy is possible with ~300 events if source contribution is 10-15%.

The threshold fraction for anisotropy detection decreases with larger sample sizes.

Results are applicable to other future experiments with uniform celestial exposure.

Abstract

KLYPVE-EUSO (K-EUSO) is a planned orbital detector of ultra-high-energy cosmic rays (UHECRs), which is to be deployed on board the International Space Station. K-EUSO is expected to have a uniform exposure over the celestial sphere and register from 120 to 500 UHECRs at energies above 57 EeV in a 2-year mission. We employed the TransportCR and CRPropa 3 packages to estimate prospects of detecting a large-scale anisotropy of ultra-high-energy cosmic rays from a nearby source with K-EUSO. Nearby active galactic nuclei Centaurus A, M82, NGC 253, M87 and Fornax A were considered as possible sources of UHECRs. A minimal model for extragalactic cosmic rays and neutrinos by Kachelriess, Kalashev, Ostapchenko and Semikoz (2017) was chosen for definiteness. We demonstrate that an observation of $\gtrsim300$ events will allow detecting a large-scale anisotropy with a high confidence level providing the fraction of from-source events is $\simeq$10-15%, depending on a particular source. The threshold fraction decreases with an increasing sample size. We also discuss if an overdensity originating from a nearby source can be observed at around the ankle in case a similar anisotropy is found beyond 57 EeV. The results are generic and hold for other future experiments with a uniform exposure of the celestial sphere.