Unusual behavior in radio supernova SN 1993J

Here we present two near-simultaneous spectra of a Type IIb supernova, SN 1993J taken around day similar to 3200 and similar to 3700, observed with the Giant Meterwave Radio Telescope (GMRT) and Very Large Array (VLA). We show the synchrotron cooling break in the optically thin part of both the spectra. Based on these two spectra 1.5 years apart, cooling break frequency seems to be evolving with time. We calculate the magnetic field evolution and put constraints on electron diffusion coefficient from the evolution in break frequency.