Abstract

Contributed Talk - Splinter NonThermalAccel   (MW-1250)

Spectral variations between different CR species caused by abundancy gradients in the CSM of massive stars

Brose, Robert; Shi, Xin-Yue; Pohl, Martin
Universität Potsdam, DESY

It has been a long-standing paradigm that the bulk of Galactic comic-ray gets accelerated at supernova remnant (SNR) shocks via diffusive shock acceleration. As observations – both direct and indirect – became better, many features appeared in the cosmic-ray spectra at Earth and in the emission spectra of remnants, that require deviations from the expectation of a simple power-law of accelerated particles with a power-law index of s=-2. Here, we demonstrate how the presence of a abundancy-gradients in the circumstellar medium (CSM) around core-collapse SNR can cause slight differences in spectral indices of different CR-species. We use RATPaC to simultaneously model the acceleration of various CR species at an SNR shock expanding in a CSM bubble that shows abundancy gradients. The burning of hydrogen over time leads to an increasing hydrogen-fraction from the vicinity of the star towards the edge of the wind-bubble, while the helium fraction is usually decreasing with distance. Such a situation causes a softening of the hydrogen spectrum with respect to helium - a feature observed for CRs measured at Earth. The relative spectral difference is dependent on the strength of the abundancy gradient and the acceleration time of CRs and provides an alternative channel for constraining the turbulence conditions at SNR shocks.