Spectral curvature and breaks from Fermi acceleration at oblique shocks

Asma Shirin T; Brian Reville; Nils W. Schween; Florian Schulze; John G. Kirk

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arXiv · 2511.01635

Spectral curvature and breaks from Fermi acceleration at oblique shocks

Asma Shirin T·Brian Reville·Nils W. Schween·Florian Schulze·John G. Kirk

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Abstract

A major attraction of diffusive shock acceleration is the prediction of power-law spectra for energetic particle distributions. However, this property is not fundamental to the theory. We demonstrate that for planar shocks with an oblique magnetic field the generation of power-law spectra critically requires the particles' scattering rate to be both directly proportional to their gyro radius (Bohm scaling) and spatially uniform. Non-Bohm scaling results in curved spectra at oblique shocks, while abrupt changes in the spatial profile of the scattering upstream introduces spectral breaks. Using the publicly available code Sapphire++, we numerically explore the magnitude of these effects, which are particularly pronounced at fast shocks, as expected in active galactic nuclei and microquasar jets, or young supernova remnants.

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Asma Shirin T, Brian Reville, Nils W. Schween, Florian Schulze, John G. Kirk. 2025-11-03. Spectral curvature and breaks from Fermi acceleration at oblique shocks. https://arxiv.org/abs/2511.01635

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