Diffusive shock acceleration of dust grains at supernova remnants

Context. Diffusive shock acceleration (DSA) is a prominent mechanism for energizing charged particles up to very large rigidities at astrophysical collisionless shocks. In addition to ions and electrons, it has been proposed that interstellar dust grains could also be accelerated through diffusive shock acceleration; for instance, at supernova remnants (SNRs). Aims. Considering interstellar dust grains of various sizes and compositions, we investigate the possibility of grain acceleration at young SNR shocks (throughout the free expansion and Sedov-Taylor phases) and the maximum energies reached by the accelerated grains. We investigate the potential implications for the abundance of refractory species relative to volatile elements in the cosmic-ray composition. Methods. We rely on semi-analytical descriptions of particle acceleration at strong shocks, and on self-similar solutions for the dynamics of SNR shock waves. For simplicity, type Ia thermonuclear SNRs expanding in a uniform interstellar medium are considered. Results. We find that the acceleration of dust grains at relativistic speed is possible, up to a Lorentz factor of ∼10 2 and a kinetic energy of E k /nuc ∼ 10 2 GeV/nuc for the smaller grains of size a ∼ 5 × 10 −7 cm. We find that the subsequent sputtering of grains can produce nuclei with a sufficient rigidity to be injected in the process of diffusive shock acceleration. Such a scenario can help naturally account for the overabundance of refractory elements in the Galactic cosmic-ray composition, provided that a fraction, η ∼ 10 −3 − 10 −2 , of dust grains swept up by an SNR are energized through DSA.