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CRPropa 3.3: Toward a Unified Multi-Messenger Framework from GeV to ZeV Energies

Sophie Aerdker, Rafael Alves Batista, Julia Becker Tjus, Gaetano Di Marco, Julien Dörner, Karl-Heinz Kampert, Lukas Merten, Leonel Morejon, Gero Müller, Patrick Reichherzer, Andrey Saveliev, Leander Schlegel, Günter Sigl, Arjen van Vliet

TL;DR

This paper presents CRPropa 3.3, a public Monte Carlo framework for simulating high-energy particle propagation across Galactic and extragalactic environments for multi-messenger astrophysics in the $GeV$–$ZeV$ regime. It introduces time tracking, time-dependent advection, and position-dependent radiation fields, alongside heavy nuclei up to $Z=82$ and spatial ISRF grids, enabling more realistic, time-resolved simulations. Key contributions include new Galactic magnetic field models, updated EBL models, a restart capability, and the integration of moving-shock acceleration and external plugins, all within a modular, extensible platform. The work advances unified modeling of cosmic rays, gamma rays, and secondaries, with practical impact for next-generation multi-messenger studies and broader accessibility to the community.

Abstract

We present CRPropa 3.3, the latest release of the publicly available Monte Carlo framework for simulating the propagation of high-energy particles in astrophysical environments. This version introduces significant extensions that enables multi-messenger studies across a broad energy range, from GeV to ZeV. New features include explicit time tracking, time-dependent advection fields, and support for position-dependent radiation backgrounds, for more realistic simulations of Galactic and extragalactic propagation. Nuclear cross sections have been updated and expanded up to lead (Z=82). We illustrate some of these new features, including acceleration at moving shocks and gamma-ray propagation in the interstellar radiation field. Together, these improvements establish CRPropa 3.3 as a comprehensive tool for modelling cosmic rays, gamma rays, and their secondaries in structured, time-dependent environments, setting the stage for next-generation multi-messenger astrophysics.

CRPropa 3.3: Toward a Unified Multi-Messenger Framework from GeV to ZeV Energies

TL;DR

This paper presents CRPropa 3.3, a public Monte Carlo framework for simulating high-energy particle propagation across Galactic and extragalactic environments for multi-messenger astrophysics in the – regime. It introduces time tracking, time-dependent advection, and position-dependent radiation fields, alongside heavy nuclei up to and spatial ISRF grids, enabling more realistic, time-resolved simulations. Key contributions include new Galactic magnetic field models, updated EBL models, a restart capability, and the integration of moving-shock acceleration and external plugins, all within a modular, extensible platform. The work advances unified modeling of cosmic rays, gamma rays, and secondaries, with practical impact for next-generation multi-messenger studies and broader accessibility to the community.

Abstract

We present CRPropa 3.3, the latest release of the publicly available Monte Carlo framework for simulating the propagation of high-energy particles in astrophysical environments. This version introduces significant extensions that enables multi-messenger studies across a broad energy range, from GeV to ZeV. New features include explicit time tracking, time-dependent advection fields, and support for position-dependent radiation backgrounds, for more realistic simulations of Galactic and extragalactic propagation. Nuclear cross sections have been updated and expanded up to lead (Z=82). We illustrate some of these new features, including acceleration at moving shocks and gamma-ray propagation in the interstellar radiation field. Together, these improvements establish CRPropa 3.3 as a comprehensive tool for modelling cosmic rays, gamma rays, and their secondaries in structured, time-dependent environments, setting the stage for next-generation multi-messenger astrophysics.

Paper Structure

This paper contains 14 sections, 3 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Technical improvements
  3. New Galactic magnetic field models
  4. New EBL models
  5. Explicit time dependence
  6. Other improvements
  7. New features
  8. Inclusion of nuclei up to lead
  9. Position-dependent radiation field
  10. New physics use cases
  11. Position-dependent radiation fields
  12. Acceleration at moving shocks
  13. External plugins
  14. Summary and Outlook

Figures (5)

  • Figure 1: Nuclear species included in version 3.3, compared to the previously implemented ones.
  • Figure 2: Relative difference between thinned and unthinned channel selection for all nuclei included. Photon energy in the rest frame of the nucleus.
  • Figure 3: Nodes at the galactic plane, seen from above, of the ISRF grid from the F98 model. The colour bar refers to the integrated energy density of the radiation field at each node.
  • Figure 4: Observation of the source 1LHAASOJ1825-1256u by LHAASO-KM2A, modelled as a power law with uncertainties cao2024first. The simulated spectra, including Galactic photon backgrounds, are compared to a naive extrapolation without propagation effects.
  • Figure 5: Left: Shock profiles and space-energy histogram in lab frame. Pseudo-particles are injected in the undisturbed medium, the shock is moving through it. Right: Stationary wind profile and space-energy histogram. Pseudo-particles are injected at the shock. For both columns, the top row shows spectra and wind profiles at $T=50$ and the bottom row shows them at $T=90$.