Non-thermal neutrinos from supernovae leaving a magnetar
Under the fossil field hypothesis of the origin of magnetar magnetic fields, the magnetar inherits its magnetic field from its progenitor. We show that during the supernova of such a progenitor, protons may be accelerated to \sim 10^4 GeV as the supernova shock propagates in the magnetic stellar envelope. Inelastic nuclear collisions of these protons produce a flash of high-energy neutrinos arriving a few hours after thermal (10 MeV) neutrinos. The neutrino flash is characterized by energies up to O(100) GeV and durations seconds to hours, depending on the progenitor: those from smaller Type Ibc progenitors are typically shorter in duration and reach higher energies compared to those from larger Type II progenitors. A Galactic Type Ib supernova leaving behind a magnetar remnant will yield up to \sim 160 neutrino induced muon events in Super-Kamiokande, and up to \sim 7000 in a km^3 class detector such as IceCube, providing a means of probing supernova models and the presence of strong magnetic fields in the stellar envelope.