Abstract
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 the High-Altitude Water Cherenkov Observatory.
Highlights
The search for sources of cosmic rays at energies above 1015 eV remains one of the key challenges in high-energy astrophysics
The exploration of this scenario is important as the reported HAWC ultra-high-energy (UHE) sources exhibit no obvious correlation with target material as would be expected in the hadronic scenario, and all are associated with young and powerful pulsars
As shown in this Letter, hard Inverse Compton (IC) spectra up to and beyond 100 TeV are possible wherever IC losses dominate over synchrotron losses for sufficiently high energies
Summary
The search for sources of cosmic rays at energies above 1015 eV remains one of the key challenges in high-energy astrophysics. In specific circumstances the emission of accelerated electrons may produce spectra compatible with these observations: in particular when electron cooling is dominated by IC losses (Blumenthal & Gould 1970; Zdziarski & Krolik 1993; Hinton & Aharonian 2007). The exploration of this scenario is important as the reported HAWC ultra-high-energy (UHE) sources exhibit no obvious correlation with target material as would be expected in the hadronic scenario, and all are associated with young and powerful pulsars.
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