Grammage of cosmic rays in the proximity of supernova remnants embedded in a partially ionized medium

Abstract

We investigate the damping of Alfvén waves generated by the cosmic ray resonant streaming instability in the context of the cosmic ray escape and propagation in the proximity of supernova remnants. We consider ion-neutral damping, turbulent damping and non linear Landau damping in the warm ionized and warm neutral phases of the interstellar medium. For the ion-neutral damping, up-to-date damping coefficients are used. We investigate in particular whether the self-confinement of cosmic rays nearby sources can appreciably affect the grammage. We show that the ion-neutral damping and the turbulent damping effectively limit the residence time of cosmic rays in the source proximity, so that the grammage accumulated near sources is found to be negligible. Contrary to previous results, this also happens in the most extreme scenario where ion-neutral damping is less effective, namely in a medium with only neutral helium and fully ionized hydrogen. Therefore, the standard picture, in which CR secondaries are produced during the whole time spent by cosmic rays throughout the Galactic disk, need not to be deeply revisited.

Probing the origin of 4FGL J0822.8-4207: cosmic ray illumination from the SNR Puppis A and the Herbig-Haro object HH219

“…The normalization of the diffusion coefficient, as well as δ, could be modified by the amplification of Alfvén waves by cosmic rays (Fujita et al 2011;Malkov et al 2013). A modification is also expected even if the waves suffer from different types of damping (Recchia et al 2021).…”

Enhancement of the non-resonant streaming instability by particle collisions

“…The initial background proton thermal energy was taken as k B T m = m p v 2 A0 = 1 eV. We note that for smaller energies the charge exchange collisions, where the ion takes an electron from the neutral particle, cannot be dissociated from the elastic collisions for proton-hydrogen interactions [30]. In such a case the friction force used in Ref.…”

“…In a collisional plasma, pressure anisotropies may be mitigated if collisions are sufficiently frequent to redistribute the energy in all directions of space. Here we investigate two cases: a fully ionized background plasma such that ion Coulomb collisions are dominant, and a poorly ionized background where collisions with a population of neutrals are dominant, the latter being important for example in the warm neutral medium [30]. Because the NR mode relies on bulk fluid motions to grow, one would expect that intraspecies Coulomb collisions, which conserve momentum and energy [31], do not modify the growth of the instability.…”

Self-confinement of low-energy cosmic rays around supernova remnants

“…Subsequently, Nava et al [10,11] solved the equations numerically including the effect of damping, also providing an estimate for the escape time. Most recently Brahimi et al [12] investigated the propagation into the inhomogeneous interstellar medium and Recchia et al [13] refined the coupling of ions and neutrals for particles down to 10 GeV.…”

“…Answering the above questions thus requires a better modelling of self-confinement of CRs below 10 GeV around SNRs. However, low-energy CRs undergo significant energy losses which the previously used setups could not cover [10,11,13] due to the choice of numerical methods used. Here, we will propose an extended framework which will be able to take into account the energy losses which allows us to model the self-confinement of CRs below 10 GeV.…”