Implications of aging in young supernovae

We present here the combined radio spectrum from the Giant Metrewave Radio Telescope (GMRT) and Very Large Array (VLA) of type-IIb SN 1993J (age 11 years) and a type-Ic SN 2003bg (age 1 year). In SN 1993J, we find a break in the spectrum at 4 GHz and associate it with Synchrotron cooling break. Hence, we determine the magnetic field independent of equipartition assumption between relativistic electrons and magnetic energy. We also see a hint of break in the spectrum of SN 2003bg between 22-40 GHz. The spectrum of SN 2003bg is well described by the synchrotron self absorption model.