SNART: Synchrotron Self Absorption Model For Non-relativistic Transients

Abstract

We present SNART (DeMarchi & Finstad ), software for radio synchrotron self-absorption analysis, a generalized version of the model introduced in Chevalier, Chevalier & Fransson. SNART ingests flux density and frequency observations, fits them jointly, and outputs system physical parameters: magnetic field B, shock radius R, post shock energy U, electron number density n e , circumstellar density ρ CSM, and mass loss degenerate with wind velocity . SNART is written in Python and is publicly available via GitHub. The repository hosts an in-depth derivation of the model and a detailed description of parameter definitions in the literature. SNART is a generalized treatment of synchrotron self absorption that leaves the choice of values for p (the power-law index of the electron distribution), q (shock front acceleration), θ (electron pitch angle, commonly π/2), and f (the “filling factor,” often 0.5) explicit.