PeV-EeV neutrinos from gamma-ray blazars due to ultrahigh-energy cosmic-ray propagation

TL;DR

This paper investigates how gamma-ray blazars contribute to PeV-EeV neutrinos through cosmic-ray interactions, analyzing their impact on the diffuse neutrino background and related electromagnetic cascades.

Contribution

It models the neutrino flux from blazars considering cosmic-ray interactions with EBL and CMB, incorporating redshift distribution and unresolved sources, providing new insights into their contribution to high-energy neutrinos.

Findings

Up to 10% of the PeV neutrino flux may originate from cosmic-ray interactions with EBL.

Electromagnetic cascades from secondary particles are constrained by gamma-ray observations.

The baryonic loading factor depends on the maximum cosmic-ray energy and observed fluxes.

Abstract

Blazars are potential candidates of cosmic-ray acceleration up to ultrahigh energies ($E\gtrsim10^{18}$ eV). For an efficient cosmic-ray injection from blazars, $p\gamma$ collisions with the extragalactic background light (EBL) and cosmic microwave background (CMB) can produce neutrino spectrum peaks near PeV and EeV energies, respectively. We analyze the contribution of these neutrinos to the diffuse background measured by the IceCube neutrino observatory. The fraction of neutrino luminosity originating from individual redshift ranges is calculated using the distribution of BL Lacs and FSRQs provided in the \textit{Fermi}-LAT 4LAC catalog. Furthermore, we use a luminosity dependent density evolution to find the neutrino flux from unresolved blazars. The results obtained in our model indicate that as much as $\approx10\%$ of the flux upper bound at a few PeV energies can arise from cosmic-ray interactions on EBL. The same interactions will also produce secondary electrons and photons, initiating electromagnetic cascades. The resultant photon spectrum is limited by the isotropic diffuse $\gamma$-ray flux measured between 100 MeV and 820 GeV. The latter, together with the observed cosmic-ray flux at $E>10^{16.5}$ eV, can constrain the baryonic loading factor depending on the maximum cosmic-ray acceleration energy.