ASGARD: GRB Afterglow Analysis Tool

A Standard GRB afterglow Radiation Diagnoser (ASGARD) is a state-of-the-art simulation code for GRB afterglow.

The code is entirely based on numerical partial differential equation methods to solve the evolution of the afterglow electron spectrum, while precisely handling the cooling process of electrons via Compton scattering. It self-consistently computes synchrotron radiation and synchrotron self-Compton (SSC) radiation using high-order integration schemes and fully accounts for observational effects. The calculated afterglow radiation spectrum covers the entire electromagnetic range from radio to very high energies (VHE), with proper treatment of synchrotron self-absorption (SSA, based on radiative transfer) and $\gamma\gamma$ annihilation (based on scattering cross-sections).

The code's greatest strengths lie in its exceptional computational efficiency and accuracy. When employing the default first-order fully implicit scheme to solve the electron continuity equation, the code can rapidly and stably generate results even under extreme conditions, such as very strong magnetic fields ($\epsilon_B \sim 1$) and high ambient medium particle densities ($n \gg 10^6 , \text{cm}^{-3}$). When using the WENO5 scheme, the code achieves fifth-order accuracy in resolving the electron spectrum. The calculation of synchrotron and SSC radiation is based on the composite Simpson's method (O($N^4$)).

ASGARD is written in Fortran, and its computational processes are highly parallelized using OpenMP. When combined with MPI parallelization schemes employing emcee or pymultinest samplers, the code can operate with extremely high efficiency on personal computers, workstations, and even computing clusters. For instance, in the case of on-axis-viewed top-hat jet synchrotron radiation, sampling a million times on a single-node dual-socket EPYC 9754 system requires only a few hours.

What has been updated recently?

1. The interface for energy injection has been opened, supporting energy injection in the form of black hole accretion.
2. Added density jump behavior in a uniform environment, enabling the modeling of a dense shell (e.g., a gas cloud) or a cavity at a distance R from the progenitor star radius, with a density profile following a log-Gaussian distribution.
3. Added output for the characteristic synchrotron radiation frequencies: $\nu_m$, $\nu_c$, and $\nu_a$.
4. Now we use the meson-based f2py compilation process, which significantly accelerates the build. Moreover, this improvement allows us to lift the previous restrictions on Python versions—only require Python >= 3.8 as a baseline.

Current progress

1. Make $\chi^2$ calculation and extinction correction modules Standardization.

License

Copyright (c) 2025 Jia Ren

This source code is governed by the BSD 3-Clause License.

Attribution Requirement

If you use, adapt, or reference the core algorithms from this project in other software projects (whether open-source or proprietary), you are required to provide explicit attribution to this original code project in your project's documentation, 'About' section, or any publicly published papers.

Recommended Citation Format

@ARTICLE{2024ApJ...962..115R,
       author = {{Ren}, Jia and {Wang}, Yun and {Dai}, Zi-Gao},
       title = "{Jet Structure and Burst Environment of GRB 221009A}",
       journal = {\apj},
       keywords = {Gamma-ray bursts, 629, Astrophysics - High Energy Astrophysical Phenomena},
         year = 2024,
        month = feb,
       volume = {962},
       number = {2},
          eid = {115},
        pages = {115},
          doi = {10.3847/1538-4357/ad1bcd},
       archivePrefix = {arXiv},
       eprint = {2310.15886},
       primaryClass = {astro-ph.HE},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...962..115R},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}

This project name is ASGARD, Retrieved from https://github.com/mikuru1096/ASGARD_GRBAfterglow

Quick Start

The usage of this code is very simple. Ensure you have GNU compilers, python >=3.8, numpy, astropy, scipy, and matplotlib installed on your system. For Ubuntu/Debian systems:

sudo apt install gcc g++ gfortran

Clone this repository to your local machine:

git clone https://github.com/mikuru1096/ASGARD_GRBAfterglow
cd ASGARD_GRBAfterglow

Install dependencies

pip install -r Requirements.txt

Run the installation script:

bash install.sh

After compilation completes, run:

python hand_my.py

If you already have the matplotlib package installed, the program should generate the first multi-band afterglow light curve image for you.

Documentation

In mergered.py, we have provided the basic invocation method of the program, along with simple comments for the keywords.

Current Status

Due to current progress limitations, we are not yet able to provide a complete demonstration of the afterglow fitting workflow. However, please start exploring and try to integrate it into your own fitting framework!

Web Interface

We have a website available at https://hetools.xyz
that requires no installation, for comparing the results of ASGARD and jetsimpy. Feel free to give it a try!