Radius and magnetic field from Synchrotron-self-absorbed radio and   Inverse Compton X-ray observations of Supernovae
  Simple expressions for the radius and magnetic field of a system emitting Synchrotron-self-absorbed radio and Inverse Compton X-rays are derived from first principles which involve observable quantities only. These expressions are useful for analyzing observations of Supernova blastwaves interacting with dense circumstellar material at early times. 
Boaz Katz
astro-ph.HE