The Origin of Present Day Cosmic Rays: Fresh SN Ejecta or Interstellar Medium Material ? II Physics of the SNR shock wave acceleration

Abstract

Assuming that refractory elements in cosmic rays originate in dust grains, we examine the viability of cosmic ray origin models wherein the bulk of present day cosmic rays are accelerated out of fresh supernova ejecta material before it mixes with the average interstellar medium (ISM). We conclude that the fresh ejecta scenarios that have been proposed thus far have serious flaws, and are unable to account for known properties of present day cosmic rays. These flaws include: (1) the small fraction of ejecta to ISM mass processed by the forward supernova remnant (SNR) shock; (2) the difficulty fresh ejecta grains have in reaching the forward shock in isolated SNRs, and the small expected sputtering yield, especially ahead of the shock, even if grains do reach the forward shock; (3) the implausibility that fresh ejecta material can dominate cosmic ray production in diffuse superbubbles; and (4) the lack of a connection in fresh ejecta models between the production of cosmic ray refractory and volatile elements. We conclude that the near linear increase in Be abundance with metallicity observed in old, halo stars cannot imply that a significant fraction of the cosmic rays seen today come from fresh supernova ejecta. This conclusion is supported by the analysis of the present day cosmic ray composition, as shown in Meyer & Ellison, this volume.