Early Radiation Field and High-energy Electrons in Supernovae

Abstract

THE discovery of an X-ray source associated with the Crab Nebula1,2 has prompted an intensive search for X-ray sources associated with other known Type I supernovae, for example, Tycho, and Kepler3,4. 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.