Highlight: Galactic Cosmic Ray Acceleration with Steep Spectra

Discussion timeslot (ZOOM-Meeting): 20. July 2021 - 16:00
ZOOM-Meeting URL: https://desy.zoom.us/j/92846730262
ZOOM-Meeting ID: 92846730262
ZOOM-Meeting Passcode: ICRC2021
Corresponding Session: https://icrc2021-venue.desy.de/channel/Plenary-Highlight-08/106
Live-Stream URL: https://icrc2021-venue.desy.de/livestream/Plenary-01/1

Abstract:
'Galactic cosmic rays (CRs) are accelerated by astrophysical shocks, primarily supernova remnants (SNRs), via diffusive shock acceleration (DSA), an efficient mechanism that predicts power-law energy distributions of CRs. However, observations of both nonthermal SNR emission and Galactic CRs imply CR spectra that are steeper than the standard DSA prediction, $propto E^{-2}$. Recent kinetic hybrid simulations suggest that such steep spectra may be the result of a ``postcursor”, or drift of CRs and magnetic structures with respect to the thermal plasma behind the shock. Using a semi-analytic model of non-linear DSA, we generalize this result to a wide range of astrophysical shocks. By accounting for the presence of a postcursor, we produce CR energy distributions that are substantially steeper than $E^{-2}$ and consistent with observations. Our formalism reproduces both modestly steep spectra of Galactic SNRs ($propto E^{-2.2}$) and the very steep spectra of young radio supernovae ($propto E^{-3}$).'

Authors: Rebecca Diesing | Damiano Caprioli
Indico-ID: 488
Proceeding URL: https://pos.sissa.it/395/029