High-energy cosmic rays and neutrinos from semirelativistic hypernovae

The origin of the ultrahigh-energy (UHE) cosmic rays (CRs) from the second knee (∼6×10¹⁷eV) above in the CR spectrum is still unknown. Recently, there has been growing evidence that a peculiar type of supernovae, called hypernovae, are associated with subenergetic gamma-ray bursts, such as SN1998bw/GRB980425 and SN2003lw/GRB031203. Such hypernovae appear to have high (up to mildly relativistic) velocity ejecta, which may be linked to the subenergetic gamma-ray bursts. Assuming a continuous distribution of the kinetic energy of the hypernova ejecta as a function of its velocity E_k∝(Γβ)^-α with α∼2, we find that (1) the external shock wave produced by the high-velocity ejecta of a hypernova can accelerate protons up to energies as high as 10¹⁹eV; (2) the cosmological hypernova rate is sufficient to account for the energy flux above the second knee; and (3) the steeper spectrum of CRs at these energies can arise in these sources. In addition, hypernovae would also give rise to a faint diffuse UHE neutrino flux, due to pγ interactions of the UHE CRs with hypernova optical-UV photons.