Ben S. Prather
Interpretation of resolved polarized images of black holes by the Event Horizon Telescope (EHT) requires predictions of the polarized emission observable by an Earth-based instrument for a particular model of the black hole accretion system. Such predictions are generated by general relativistic radiative transfer (GRRT) codes, which integrate the equations of polarized radiative transfer in curved spacetime. A selection of ray-tracing GRRT codes used within the EHT collaboration is evaluated for accuracy and consistency in producing a selection of test images, demonstrating that the various methods and implementations of radiative transfer calculations are highly consistent.
Elad Steinberg
This work generalizes the discrete implicit Monte-Carlo (DIMC) method for modeling the radiative transfer equation from a gray treatment to an frequency-dependent one. The classic implicit Monte-Carlo (IMC) algorithm, that has been used for several decades, suffers from a well-known numerical problem, called teleportation, where the photons might propagate faster than the exact solution due to the finite size of the spatial and temporal resolution. The Semi-analog Monte-Carlo algorithm proposed the use of two kinds of particles, photons and material particles that are born when a photon is absorbed.
Shing-Chi Leung
Ongoing MeV telescopes such as INTEGRAL/SPI and Fermi/GBM, and proposed telescopes including the recently accepted COSI and the e-ASTROGAM and AMEGO missions, provide another window in understanding transients. Their signals contain information about the stellar explosion mechanisms and their corresponding nucleosynthesis of short-lived radioactive isotopes. This raises the need of a radiative transfer code which may efficiently explore different types of astrophysical $γ$-ray sources and their dependence on model parameters and input physics.
Damien Korber
With the advent of the Square Kilometre Array Observatory (SKAO), scientists will be able to directly observe the Epoch of Reionization by mapping the distribution of neutral hydrogen at different redshifts. While physically motivated results can be simulated with radiative transfer codes, these simulations are computationally expensive and can not readily produce the required scale and resolution simultaneously. Here we introduce the Physics-Informed neural Network for reIONization (PINION), which can accurately and swiftly predict the complete 4-D hydrogen fraction evolution from the smoothed gas and mass density fields from pre-computed N-body simulation.
Patrick Chi-Kit Cheong
We present the implementation of two-moment based general-relativistic multi-group radiation transport module in the $\texttt{G}$eneral-relativistic $\texttt{mu}$ltigrid $\texttt{nu}$merical ($\texttt{Gmunu}$) code. On top of solving the general-relativistic magnetohydrodynamics and the Einstein equations with conformally flat approximations, the code solves the evolution equations of the zeroth- and first-order moments of the radiations. Analytic closure relation is used to obtain the higher order moments and close the system. The finite-volume discretisation has been adopted for the radiation moments.
Yuanyuan Yang
In this paper, we present the formalism of simulating Lyman-$α$ emission and polarization around reionization ($z$ = 8) from a plane-parallel ionization front. We accomplish this by using a Monte Carlo method to simulate the production of a Lyman-$α$ photon, its propagation through an ionization front, and the eventual escape of this photon. This paper focuses on the relation of the input parameters of ionization front speed $U$, blackbody temperature $T_{\rm bb}$, and neutral hydrogen density $n_{\rm HI}$, on intensity $I$ and polarized intensity $P$ as seen by a distant observer.
A. Corporaal
(abridged) Stable circumbinary discs around evolved post-Asymptotic Giant branch (post-AGB) binary systems show many similarities with protoplanetary discs around young stellar objects. These discs can provide constraints on both binary evolution and the formation of macrostructures within circumstellar discs. Here we focus on one post-AGB binary system: IRAS08544-4431. We aim to refine the physical model of IRAS08544-4431 with a radiative transfer treatment and continue the near-infrared and mid-infrared interferometric analysis covering the H-, K-, L-, and N-bands.
Rune Strandberg
When the quality of multijunction solar cells becomes sufficiently high, radiative exchange of photons between cells has to be taken into account to properly model these devices. In this work it is shown how this radiative coupling can be accounted for in series connected multi-junction solar cells by constants called transfer coefficients. Under the assumption that the exchanged radiation only travels one way, from higher to lower band gaps, the transfer coefficients allows the relation between the voltage and current of the device to be expressed by a convenient mathematical expression.
First author: Xingzhuo Chen
Following our previous study of Artificial Intelligence Assisted Inversion (AIAI) of supernova analyses \citep{Xingzhuo2020AIAI}, we trained a set of deep neural networks based on the one-dimensional radiative transfer code TARDIS \citep{tardis} to simulate the optical spectra of Type Ia supernovae (SNe~Ia) between 10 and 40 days after the explosion. The neural network can be applied to derive the elemental abundances from the observed spectra. In this paper, we focus on the mass of $^{56}$Ni and its associated spectral features for a sample of 153 well-observed SNe~Ia.
First author: A. Bensberg
Aims. We present an implementation of an algorithm for 3D time-dependent Monte Carlo radiative transfer. It allows one to simulate temperature distributions as well as images and spectral energy distributions of the scattered light and thermal reemission radiation for variable illuminating and heating sources embedded in dust distributions, such as circumstellar disks and dust shells on time scales up to weeks. Methods. We extended the publicly available 3D Monte Carlo radiative transfer code POLARIS with efficient methods for the simulation of temperature distributions, scattering, and thermal reemission of dust distributions illuminated by temporally variable radiation sources.
