# hammurabi X: Simulating Galactic Synchrotron Emission with Random Magnetic Fields

## TL;DR

The paper introduces an updated version of the hammurabi simulator for Galactic polarized emission, featuring modern C++ implementation, multi-threading, and new methods for simulating divergence-free Gaussian random magnetic fields, with applications to synchrotron foregrounds.

## Contribution

It presents a fully renewed, multi-threaded version of the hammurabi simulator with new techniques for modeling divergence-free Gaussian magnetic fields in Galactic synchrotron emission.

## Key findings

- Gaussian random magnetic fields can produce B/E polarization ratios below unity.
- New methods enable efficient simulation of divergence-free magnetic fields on Galactic and local scales.
- The updated simulator improves computational performance and modeling accuracy.

## Abstract

We present version X of the hammurabi package, the HEALPix-based numeric simulator for Galactic polarized emission. Improving on its earlier design, we have fully renewed the framework with modern C++ standards and features. Multi-threading support has been built in to meet the growing computational workload in future research. For the first time, we present precision profiles of hammurabi line-of-sight integral kernel with multi-layer HEALPix shells. In addition to fundamental improvements, this report focuses on simulating polarized synchrotron emission with Gaussian random magnetic fields. Two fast methods are proposed for realizing divergence-free random magnetic fields either on the Galactic scale where a field alignment and strength modulation are imposed, or on a local scale where more physically motivated models like a parameterized magneto-hydrodynamic (MHD) turbulence can be applied. As an example application, we discuss the phenomenological implications of Gaussian random magnetic fields for high Galactic latitude synchrotron foregrounds. In this, we numerically find B/E polarization mode ratios lower than unity based on Gaussian realizations of either MHD turbulent spectra or in spatially aligned magnetic fields.