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arXiv · 2609.35093

Investigating signatures of extinct PeVatron activity in supernova remnants IC 443 and W51 C

Silvia Celli·Giovanni Morlino
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Abstract

Context. Supernova remnants (SNRs) are renewed sources of non-thermal particles and the main contributors of Galactic cosmic rays (CRs). Recent ultra-high energy (UHE) gamma-ray data from middle-aged SNRs, such as IC 443 and W51 C, highlight the key role of these systems for particle acceleration. Understanding SNR contribution to PeV CRs requires a detailed modelling about how accelerated particles escape their shocks and are released inside the Galaxy. Aims. We aim at critically assessing the SNR paradigm for the origin of Galactic CRs by investigating the expected secondary radiation produced by hadronic collisions of confined and escaping protons in SNRs, and compare these to recent UHE observations. Methods. Through a time-dependent analytical model describing particle acceleration at the SNR forward shock, we investigate particle escape from the shock expanding into uniform environment and diffusing inside and outside the SNR. Results. Our results support the interpretation that the gamma-ray emission from W51 C and IC 443 is due to hadronic emission from both confined and escaping protons, allowing us to derive robust constraints on the particle maximum energy, the magnetic field amplification process, and the CR acceleration efficiency in these systems. Conclusions. We find that the acceleration efficiency is in the range 1 - 10% (2 - 12%) when the spectrum of accelerated particles is proportional to p^-4 (p^-4.3) and the in-situ diffusion coefficient is suppressed by a factor of 3-10 compared to the average Galactic value. On the other hand, the particle maximum energy ever achieved falls, by a factor of a few, below the PeV energy required to explain the CR knee in the context of SNRs only.

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Silvia Celli, Giovanni Morlino. 2026-09-28. Investigating signatures of extinct PeVatron activity in supernova remnants IC 443 and W51 C. https://arxiv.org/abs/2609.35093

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