Radiative Transfer
Finding optical signals of supernovae
After the supernova explodes, the very hot ejecta and radioactive isotopes decays and emit photons. The photons interact with surrounding electrons and nuclei, and also photons themselves. The process exchanges energy between radiation and matter due to atomic physics.
My recent project includes building a Monte-Carlo radiative transfer code to understand the gamma-ray photons. I use the code to predict the gamma ray spectra and light curve of different types of supernovae. The code is comprehensively tested for all components to make sure they reproduce known results or works in the literature.
The code are openly available on Zenodo.
The flowchart of the Monte-Carlo radiative transfer code
Gamma ray spectra of C+O nova
I post-process my C+O nova model (See Nova section) after the thermonuclear runaway takes place. The nova is weak compared to classical nova model. Still it produces an observable amount of 7Be, 13N, 18F and 22Na which can decay by electron capture or beta-plus decay. The beta-plus decay emits a positron, which recombines with surrounding electrons and forms Positronium. The Positronium later decays into 2 or 3 -photons. The 511 keV line corresponds to this process.
Gamma ray spectra of Type ia supernova
I post-process the classical W7 Type Ia supernova model to capture the interaction of gamma-ray photon in the ejecta medium after explosion. Different from a nova, most radioactive isotopes are synthesized deep inside the star. It takes a longer time for the gamma-ray signal to emerge. Once it emerges, we observe the complicated line structure from the decay of 56Ni and 56Co, and some minor contribution from 48Cr. The circles are the data point from the literature using a similar approach.