Systematic Investigation into Radio Supernovae with Markov Chain Monte Carlo Analysis: Implications for Massive Stars' Mass Loss and Shock Acceleration Physics

We present a systematic analysis of radio supernovae (SNe) to investigate the statistical tendencies of SN progenitors' mass-loss rates and shock acceleration efficiencies. We conduct parameter estimation through Markov chain Monte Carlo (MCMC) analysis for 32 radio SN samples with a clear peak observed in their light curves, and successfully fit 27 objects with the widely-used radio SN model. We find the inferred mass-loss rates of stripped-envelope SN progenitors are by an order of magnitude greater ($\sim 10^{-3}\,M_\odot{\rm yr}^{-1}$) than those of SN II progenitors ($<10^{-4}\,M_\odot{\rm yr}^{-1}$). The efficiencies of electron acceleration and magnetic field amplification are found to be less than $10^{-2}$, and the possibility of their energy equipartition is not ruled out. On the other hand, we find the following two properties that might be related to limitations of the standard model for radio SNe; one is the extremely high magnetic field amplification efficiency, and the other is the shallower density gradient of the outer ejecta. We suggest the new interpretation that these peculiar results are misleading due to the setup that is not included in our model, and we identify the missing setup as a dense CSM in the vicinity of the progenitor. This means that a large fraction of radio SN progenitors might possess dense CSM in the vicinity of the progenitor, which is not smoothly connected with the outer CSM.