Rayleigh–Taylor Instability in Interacting Supernovae: Implications for Synchrotron Magnetic Fields

Synchrotron emission from a supernova (SN) necessitates a magnetic field, but it is unknown how strong the relevant magnetic fields are, and what mechanism generates them. In this study, we perform high-resolution numerical gas dynamics calculations in axisymmetry to determine the growth of turbulence due to Rayleigh–Taylor (RT) instability, and the resulting kinetic energy in turbulent fluctuations, as a means of inferring how strong magnetic fields can become when amplified by this turbulence. Assuming rough equipartition between kinetic and magnetic energy in the turbulence, we find that RT instability may produce turbulent fluctuations strong enough to amplify magnetic fields to a few percent of equipartition with the thermal energy. This turbulence stays concentrated near the reverse shock, but averaging this magnetic energy throughout the shocked region (weighting by emissivity) sets the magnetic fields at a minimum of 0.3 percent of equipartition. This line of argument predicts a minimum effective magnetic field strength (${ϵ}_B>0.003$) that should be present in all interacting SNe. This provides a prediction for what should be found in highly resolved, three-dimensional magnetohydrodynamics calculations. The strength and spatial distribution of turbulently generated magnetic fields would have implications for the shape and luminosity of SN radio light curves.