Where are Milky Way's Hadronic PeVatrons?

TL;DR

This paper develops a new approach to identify the sources of high-energy hadronic cosmic rays in the Milky Way by analyzing gamma-ray and neutrino data, exploring scenarios where sources are either detectable or hidden.

Contribution

It introduces a population-based method to constrain the nature of Milky Way hadronic PeVatrons using multi-messenger data, considering different source scenarios.

Findings

Two extreme scenarios for PeVatrons are identified: detectable neutrino sources or hidden sources.

Current data constrains the column densities of potential hadronic accelerators.

Future observations could distinguish between the scenarios and reveal the true nature of PeVatrons.

Abstract

Observations of the Milky Way at TeV-PeV energies reveal a bright diffuse flux of hadronic cosmic rays and also bright point sources of gamma rays. If the gamma-ray sources are hadronic cosmic-ray accelerators, then they must also be neutrino sources. However, no neutrino sources have been detected. Where are they? We introduce a new population-based approach to probe Milky Way hadronic PeVatrons, demanding consistency between diffuse and point-source PeV-range data on cosmic rays, gamma rays, and neutrinos. For the PeVatrons, two extreme scenarios are allowed: (1) the hadronic cosmic-ray accelerators and the gamma-ray sources are the same objects, so that bright neutrino sources exist and improved telescopes can detect them, versus (2) the hadronic cosmic-ray accelerators and the gamma-ray sources are distinct, so that there are no detectable neutrino sources. The latter case is possible if hadronic accelerators have sufficiently thin column densities. We quantify present constraints and future prospects, showing how to reveal the nature of the hadronic PeVatrons.