Extragalactic cosmic ray sources with very small contribution in the particle flux on the Earth and their study

TL;DR

This paper explores the potential existence of extragalactic ultra-high energy cosmic ray sources with minimal particle flux reaching Earth, emphasizing their gamma-ray and neutrino emissions for indirect detection.

Contribution

It introduces a model of small-contribution extragalactic sources with hard injection spectra and highlights the importance of gamma-ray and neutrino observations for their study.

Findings

Diffuse gamma-ray emission from cascades can be significant.

Cascade neutrino spectra depend on injection spectra at high energies.

Low flux sources may be detectable via secondary emissions.

Abstract

Possible existence of extragalactic ultra-high energy cosmic ray sources giving a very small particle flux on the Earth is considered. Accretion discs around supermassive black holes where particles are accelerated in electric fields are discussed as an illustration of such sources. Due to acceleration mechanism particle injection spectra are assumed to be hard. In this case particle flux on the Earth is too low for detection. But particles produce in space a noticeable flux of diffuse gamma-ray emission via electromagnetic cascades. It should be accounted for when analyzing other source models and dark matter models. Also neutrinos are produced in cascades, and at energies E >10^19 eV cascade neutrino spectra depends on injection spectra. Therefore it is proposed to study cosmic ray sources under consideration using data on gamma-ray and neutrino emission.