TransFit-CSM: A Fast, Physically Consistent Framework for Interaction-Powered Transients

TL;DR

TransFit-CSM is a rapid, physically consistent modeling framework for interaction-powered transients that accurately fits observed supernova light curves and infers physical parameters, bridging simple models and detailed simulations.

Contribution

It introduces a novel, efficient framework that self-consistently couples shock dynamics with radiative diffusion, enabling detailed inference of supernova ejecta and CSM properties.

Findings

Successfully models SN 2006gy and SN 2010jl light curves

Reveals the importance of pre-supernova mass loss

Clarifies breakdown of Arnett-like peak scalings in thick CSM

Abstract

We present TransFit-CSM, a fast and physically consistent framework for modeling interaction-powered transients. The method self-consistently couples the ejecta circumstellar medium (CSM) shock dynamics to radiative diffusion from a moving heating boundary tied to the shocks, so that both the photon escape path and the effective diffusion time evolve with radius and time. We solve the mass and momentum equations for the forward and reverse shocks together with the diffusion equation in the unshocked CSM. TransFit-CSM reproduces the canonical sequence of an early dark phase, a diffusion-mediated rise and peak, and a post-interaction cooling tail, and it clarifies why Arnett-like peak scalings break down in optically thick CSM. The framework is well suited for Bayesian inference and constrains physical parameters of the ejecta and CSM from bolometric or joint multi-band light curves. Applications to SN 2006gy and SN 2010jl yield accurate fits and physically interpretable posteriors, highlighting the dominant role of pre-supernova mass loss in shaping the observables. Because it is both computationally efficient and physically grounded, TransFit-CSM bridges simple analytic prescriptions and radiation-hydrodynamic simulations, enabling population-level inference for current and future time-domain surveys.