Cosmic Rays from Trans-relativistic Supernovae

We derive constraints which must be satisfied by the sources of ∼ 1015 to ∼ 1018 eV cosmic rays, under the assumption that the sources are Galactic. We show that while these constraints are not satisfied by ordinary supernovae, which are believed to be the sources of . 1015 eV cosmic rays, they may be satisfied by the recently discovered class of trans-relativistic supernovae (TRSNe), supernovae associated with sub-energetic gammaray bursts. A crucial TRSN characteristic, which distinguishes them from ordinary supernovae and allows them to satisfy the derived constraints, is the deposition of a significant fraction, > 10−2, of the explosion energy in mildly relativistic, γβ > 1, ejecta. Galactic TRSNe may therefore be the sources of cosmic rays with energies up to ∼ 1018 eV. Subject headings: acceleration of particles — cosmic rays — gamma-rays: bursts — supernovae: general — supernova remnants