Ultra-high energy Inverse Compton emission from Galactic electron accelerators

TL;DR

This paper proposes that under certain environmental conditions, high-energy electrons can produce >100 TeV inverse Compton emission, challenging the assumption that such emission indicates PeV protons, and explains recent observations.

Contribution

It introduces a scenario where electron cooling allows for ultra-high energy inverse Compton emission in star-forming regions, expanding the understanding of high-energy astrophysical sources.

Findings

Hard ultra-high energy sources are likely in star-forming regions.

The scenario explains recent 100 TeV sources observed by HAWC.

Environmental conditions enable electrons to produce >100 TeV emission.

Abstract

It is generally held that >100 TeV emission from astrophysical objects unambiguously demonstrates the presence of PeV protons or nuclei, due to the unavoidable Klein-Nishina suppression of inverse Compton emission from electrons. However, in the presence of inverse Compton dominated cooling, hard high-energy electron spectra are possible. We show that the environmental requirements for such spectra can naturally be met in spiral arms, and in particular in regions of enhanced star formation activity, the natural locations for the most promising electron accelerators: powerful young pulsars. Our scenario suggests a population of hard ultra-high energy sources is likely to be revealed in future searches, and may also provide a natural explanation for the 100 TeV sources recently reported by HAWC.