Early Radiation Field and High-energy Electrons in Supernovae

Abstract

THE discovery of an X-ray source associated with the Crab Nebula^1,2 has prompted an intensive search for X-ray sources associated with other known Type I supernovae, for example, Tycho, and Kepler^3,4. So far this search has proved fruitless. One is thus led to wonder what essential differences between supernovae of the same type might result in the presence or absence of X-ray emission. Morrison and Sartori⁵ have proposed a thermal radiation model to account for this discrepancy. On the other hand, Woltjer⁶ has argued that the observed X-ray emission from the Crab Nebula is due to synchrotron radiation. I suggest that if Woltjer's hypothesis is correct, a critical part is played by the intensity of the early post-explosion radiation field; for this field, by way of the inverse Compton effect, limits the energy of the electrons in the supernova. In fact, I estimate that no extreme relativistic electrons (E > 10¹² eV) can survive the first few weeks after the explosion. The situation is somewhat similar to that which gives rise to an upper bound on the energy of cosmic-ray electrons—the inverse Compton effect from starlight and synchrotron radiation in the galactic magnetic fields forcing a limit on the electron energy⁷.