# Solving the gamma-ray radiative transfer equation for supernovae

## TL;DR

This paper introduces a new relativistic radiative-transfer code for gamma-rays in supernova ejecta, enabling accurate and fast modeling of gamma-ray transport and energy deposition, with results comparable to Monte Carlo methods.

## Contribution

The paper presents a novel relativistic radiative-transfer code for gamma-ray transport in supernovae, improving accuracy and computational speed over previous methods.

## Key findings

- Code yields results comparable to Monte Carlo simulations.
- Differences observed compared to pure absorption models.
- Synthetic spectra show asymmetric line profiles at early times.

## Abstract

We present a new relativistic radiative-transfer code for $\gamma$-rays of energy less than 5 MeV in supernova (SN) ejecta. This code computes the opacities, the prompt emissivity (i.e. decay), and the scattering emissivity, and solves for the intensity in the co-moving frame. Because of the large expansion velocities of SN ejecta, we ignore redistribution effects associated with thermal motions. The energy deposition is calculated from the energy removed from the radiation field by scattering or photoelectric absorption. This new code yields comparable results to an independent Monte Carlo code. However, both yield non-trivial differences with the results from a pure absorption treatment of $\gamma$-ray transport. A synthetic observer's frame spectrum is also produced from the CMF intensity. At early times when the optical depth to $\gamma$-rays is large, the synthetic spectrum show asymmetric line profiles with redshifted absorption as seen in SN 2014J. This new code is integrated within CMFGEN and allows for an accurate and fast computation of the decay energy deposition in SN ejecta.