Blazar Flares as an Origin of High-Energy Cosmic Neutrinos?

TL;DR

This paper investigates the role of blazar flares in producing high-energy cosmic neutrinos, analyzing their contribution to the diffuse neutrino background and multi-messenger observational constraints.

Contribution

It introduces a two-zone model for blazar flares that aligns with X-ray and gamma-ray observations while explaining neutrino production.

Findings

Blazars contribute less than 10% to the diffuse neutrino flux at sub-PeV energies.

Luminous neutrino flares are likely accompanied by bright X-ray and gamma-ray emission.

Detection rate of energetic blazar flares is estimated to be less than one per year.

Abstract

We consider implications of high-energy neutrino emission from blazar flares, including the recent event IceCube-170922A and the 2014-2015 neutrino flare that could originate from TXS 0506+056. First, we discuss their contribution to the diffuse neutrino intensity taking into account various observational constraints. Blazars are likely to be subdominant in the diffuse neutrino intensity at sub-PeV energies, and we show that blazar flares like those of TXS 0506+056 could make <1-10 percent of the total neutrino intensity. We also argue that the neutrino output of blazars can be dominated by the flares in the standard leptonic scenario for their gamma-ray emission, and energetic flares may still be detected with a rate of <1 per year. Second, we consider multi-messenger constraints on the source modeling. We show that luminous neutrino flares should be accompanied by luminous broadband cascade emission, emerging also in X-rays and gamma-rays. This implies that not only gamma-ray telescopes like Fermi but also X-ray sky monitors such as Swift and MAXI are critical to test the canonical picture based on the single-zone modeling. We also suggest a two-zone model that can naturally satisfy the X-ray constraints while explaining the flaring neutrinos via either photomeson or hadronuclear processes.