Cosmogenic gamma-ray and neutrino fluxes from blazars associated with IceCube events

TL;DR

This paper investigates the potential of blazars associated with IceCube neutrino events to produce detectable cosmogenic gamma-ray and neutrino fluxes, which could reveal sources of ultrahigh-energy cosmic rays with upcoming telescopes.

Contribution

It provides the first calculations of guaranteed cosmogenic gamma-ray and neutrino fluxes from specific blazars linked to IceCube events, highlighting their detectability with future observatories.

Findings

Detection of neutrino fluxes requires UHECR luminosity about 10 times the neutrino luminosity.

Certain blazars like TXS 0506+056 are prime targets for upcoming telescopes.

Detection prospects depend on the UHECR luminosity relative to neutrino emission.

Abstract

Blazars constitute the vast majority of extragalactic $\gamma$-ray sources. They can also contribute a sizable fraction of the diffuse astrophysical neutrinos detected by IceCube. In the past few years, the real-time alert system of IceCube has led to multiwavelength follow-up of very high-energy neutrino events of plausible astrophysical origin. Spatial and temporal coincidences of these neutrino events with the high-activity state of $\gamma$-ray blazars can provide a unique opportunity to decipher cosmic-ray interactions in the relativistic jets. Assuming that blazars accelerate cosmic rays up to ultrahigh energies ($E>10^{17}$ eV), we calculate the "guaranteed" contribution to the line-of-sight cosmogenic $\gamma$-ray and neutrino fluxes from four blazars associated with IceCube neutrino events. Detection of these fluxes by upcoming $\gamma$-ray imaging telescopes like CTA and/or by planned neutrino detectors like IceCube-Gen2 may lead to the first direct signature(s) of ultrahigh-energy cosmic-ray (UHECR) sources. We find that detection of the cosmogenic neutrino fluxes from the blazars TXS~0506+056, PKS~1502+106 and GB6~J1040+0617 would require UHECR luminosity $\gtrsim 10$ times the inferred neutrino luminosity from the associated IceCube events. Blazars TXS~0506+056, 3HSP~J095507.9+355101 and GB6~J1040+0617 can be detected by CTA if the UHECR luminosity is $\gtrsim 10$ times the neutrino luminosity inferred from the associated IceCube events. Given their relatively low redshifts and hence total energetics, TXS~0506+056 and 3HSP~J095507.9+355101 should be the prime targets for upcoming large neutrino and $\gamma$-ray telescopes.