New Class of High-Energy Transients from Crashes of Supernova Ejecta
  with Massive Circumstellar Material Shells
  A new class of core-collapse supernovae (SNe) has been discovered in recent
years by optical/infrared surveys; these SNe suggest the presence of one or
more extremely dense (~10^5-10^11 cm^-3) shells of circumstellar material (CSM)
on 10^2-10^4 AU scales. We consider the collisions of the SN ejecta with these
massive CSM shells as potential cosmic-ray (CR) accelerators. If ~10% of the SN
energy goes into CRs, multi-TeV neutrinos and/or GeV-TeV gamma rays almost
simultaneous with the optical/infrared light curves are detectable for SNe at
<20-30 Mpc. A new type of coordinated multi-messenger search for such
transients of duration ~1 - 10 months is required; these may give important
clues to the physical origin of such SNe and to CR acceleration mechanisms.
