How to turn a supernova into a PeVatron

¹ Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany
² School of Physical Sciences and Centre for Astrophysics & Relativity, Dublin City University, Glasnevin, D09 W6Y4, Ireland
³ Dublin Institute for Advanced Studies, Astronomy & Astrophysics Section, DIAS Dunsink Observatory, Dublin D15 XR2R, Ireland
⁴ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), E-28040 Madrid, Spain
⁵ Gran Sasso Science Institute, Via F.Crispi 7, 67100 L’Aquila, Italy
⁶ INFN-Laboratori Nazionali del Gran Sasso, Via G. Acitelli 22, Assergi (AQ), Italy
⁷ Centre for Space Research, North-West University, 2520 Potchefstroom, South Africa
⁸ Astronomical Observatory of Ivan Franko National University of Lviv, Kyryla i Methodia 8, 79005 Lviv, Ukraine

^⋆ Corresponding author: robert.brose@desy.de

Received: 6 December 2024
Accepted: 25 April 2025

Abstract

Context. It is important to determine which Galactic cosmic-ray (CR) sources have the ability to accelerate particles to the knee of the CR spectrum at a few peta-electronvolt (PeV). In particular, we need to consider whether supernova remnants (SNRs) could also be contributors to this process. Current models for particle acceleration in very young remnants assume the circumstellar material (CSM) consists of smooth, freely expanding winds. There is strong evidence that some supernovae (SNs) expand into much denser CSM, including dense shells ejected by eruptions shortly before explosion.

Aims. We investigate the effects of dense circumstellar shells on particle acceleration in SN shocks during the first few years post-explosion to quantify whether SNs resulting from interactions may act as PeVatrons.

Methods. We used the PION code to model the CSM around luminous blue variables (LBVs) after having a brief episode with a mass-loss rate of up to Ṁ = 2 M_⊙yr. Consequently, we performed spherically symmetric 1D simulations using our time-dependent acceleration code RATPAC, where we simultaneously solved the transport equations for CRs, magnetic turbulence, and the hydrodynamical flow of the thermal plasma in the test-particle limit.

Results. We find that the interaction with the circumstellar shells can significantly boost the maximum energy by enhancing particle escape during the onset of the shock-shell interaction, followed by the reacceleration of the shock propagating into a medium with a preamplified field. Early interactions boost the maximum energy to a greater degree and interactions within the first five months after explosion can increase E_max to levels over 1 PeV.