CRPropa Workshop 2023

25 Sept 2023, 08:30 → 27 Sept 2023, 18:00 Europe/Berlin

Ruhr University Bochum

The quantity and quality of astrophysical observations have significantly improved during the last years. Today often not only multi-wavelength – from radio to high energy gamma rays – but also multi-messenger – from cosmic rays over photons to neutrinos – data is available for various astrophysical sources. These measurements, which are sometimes showing additional strong time variations, challenge current models of cosmic-ray propagation and interaction.

CRPropa 3.2 is one of several simulation frameworks that can be used to study cosmic-ray transport, including losses and secondary production, in a broad parameter space – from Galactic transport at ~TeV energies up to the propagation of ultra-high energy cosmic rays traveling on the largest scales. 

The CRPropa workshop has been organized on a yearly basis since 2017. It has two main goals: Bringing together users and developers of CRPropa 3.2 to develop prospects of the software and interacting with other astroparticle software developers. More generally, it is our purpose to bring together the whole cosmic-ray transport community, to exchange ideas on bridging the gaps between different propagation tools.

This year’s CRPropa workshop will be organized at Ruhr University Bochum, Germany, from September 25^th to 27^th. We are planning for a mixed format including contributed and invited talks that will be mixed with plenty of time for informal discussions. To kickstart any collaborative project ideas we can provide smaller rooms after the meeting (28.-29.09) if we get notified well in advance.

More information on the organization of the workshop, e.g., abstract submission, registration, or accommodation can be found on this indico page.

Monday, 25 September

08:30 → 09:00 Registration

09:00 → 10:30 Scientific Session

09:00 Introduction Talk

Speakers: Julien Dörner (TP IV RUB), Lukas Merten

20230915_Introduction_CRPropa.pdf

09:30 CRPropa simulations for anisotropy studies

Currently, there is growing evidence of an anisotropic component in the Ultra-High-Energy Cosmic Ray (UHECR) sky with energy greater then a few EeV. However, identifying cosmic accelerators capable of reaching such high energies remains challenging due to interactions with background photons and magnetic deflection caused by cosmic fields (both galactic and extragalactic). Additionally, the strength and spacial structure of the extragalactic magnetic filed (EGMF) are still poorly understood, making the reconstruction of UHECR deflections a non-trivial task. In this study we consider constrained EGMF models within our local Universe to simulate the propagation of UHECRs through such a structured environment. By using the Monte Carlo code CRPropa3, we simulate the propagation, interactions and observation of UHECRs. The deflection of UHECRs within the galactic magnetic field (GMF) is reproduced using a lensing procedure of the UHECR arrival directions at the edge of the galaxy. We consider various combinations of source distributions, EGMF structures and mass compositions to predict the UHECR energy spectrum, mass composition and arrival direction map at Earth. For reference, we also simulate scenarios without the EGMF and with a statistically homogeneous field. We study the feasibility of constraining combinations of source distributions and EGMF models.

Speaker: Simone Rossoni

CRPropaWorkshop-2023-Rossoni.pdf

10:00 Impact of a ΛCDM extension on UHECR propagation

The existing discrepancies between the observation of local and extraction of global cosmological parameters are driving the need for an extension of the ΛCDM cosmological model. A proposed extension called SU(2)CMB describes cosmic microwave background (CMB) photons with an SU(2) instead of a U(1) gauge group. This reduces some of these tensions (such as H0, Ω𝑚, 𝜎8), pushes the recombination epoch to higher redshifts, and thereby effectively reduces CMB photon densities.

Ultra-high energy cosmic ray (UHECR) interactions with CMB photons are critical to our understanding of the observed flux of all cosmic messengers (cosmic rays, neutrinos and photons). The measured and predicted fluxes are the basis used to constrain source properties and rely on the ΛCDM CMB evolution. Thus, a modification of the past CMB densities impacts these flux predictions and possibly the constraints on the sources.

This contribution discusses the impact of the modified CMB evolution on multimessenger studies. In particular, we show the effects of the ΛCDM extension on the UHECR propagation horizon, increased cosmogenic neutrino fluxes, and the changes in source properties inferred from the UHECR spectrum.

• Supported by DFG (SFB 1491) and the Vector Foundation under grant number P2021-0102

Speaker: Janning Meinert

CRPropa Workshop - Janning Meinert.pdf

10:30 → 11:00 Coffee Break

11:00 → 12:30 Scientific Session

11:00 Normalizing Flows for Parameter Estimation of UHECR Sources with Surface Detector Data of the Pierre Auger Observatory

The combined fit of the energy spectrum and shower maximum depth distributions of ultra-high-energy cosmic rays, as measured at the Pierre Auger Observatory, can yield constraints on source parameters. These parameters include the maximum rigidity, the spectral index of the injected energy spectrum, and the initial mass composition. The relationship between the observables measured at Earth and the injection spectrum of homogeneously distributed sources can be modeled using 1-dimensional CRPropa3 simulations. For the inference of the parameters from the measured distributions, we apply a normalizing flow. We investigate the influence of higher event statistics of the depth of shower maximum distributions, which can be now extracted from the surface detector data of the Pierre Auger Observatory using deep learning. Our results indicate that the increased statistics lead to stronger constraints on the parameters. Moreover, the new dataset significantly enhances the analysis of experimental systematic effects.

Speaker: Frederik Krieger

crpropa_workshop_frederik.pdf

11:30 Population studies of UHECR sources

A key question in the field of UHECR physics is whether the observed flux is produced by a few prominent local sources or a large population of sources with similar contributions to the total flux. We constrain the ensemble of sources by investigating how diverse sources can be in terms of the maximum cosmic ray rigidity while remaining compatible with observations. We additionally study if the observed flux can be explained by two distinct source populations -- one emitting heavier cosmic rays and one producing only UHE protons. To this end, we use 1D CRPropa simulations to predict the UHECR spectrum and composition at Earth after accounting for interactions during propagation. Injection is modelled according to a simple phenomenological description but we allow for non-identical sources or a superposition of two distinct source populations. Our results show that sources contributing to the observed flux must be effectively identical in terms of maximum rigidity, although a large population of low-rigidity "hidden" sources can exist. If a two-population scenario is considered then a proton fraction of up to order of 10% is still compatible with observations.

Speaker: Domenik Ehlert

ehlert_uhecr_population.pdf

12:00 Combined fit of UHECRs with jetted AGN

We present a detailed study of the contribution of low- and high-luminosity jetted Active Galactic Nuclei (AGN) populations to the spectrum and composition of ultra-high-energy cosmic rays (UHECRs) and the corresponding EeV neutrino flux. We find that two AGN populations should have different properties to explain the UHECR data. Our results show that the dominant contribution to the neutrino flux at EeV energies comes from low-luminosity BL Lacs when using the air-shower model EPOS-LHC, while contribution of high-luminosity BL Lacs is required when using SIBYLL 2.3d. We also find that the contribution of flat-spectrum radio quasars (FSRQs) is not constrained by a fit of UHECR, but the inclusion of FSRQ is necessary to detect the neutrino flux from AGN with future instruments.

Speaker: Pavlo Plotko (DESY)

Plotko_Monday_v4.pdf

12:30 → 14:30 Lunch Break

14:30 → 15:00 Scientific Session

14:30 Towards SimProp-Sirente: the new release of the SimProp code

In my talk I will show the new advancements in SimProp development.

Speaker: Carmelo Evoli

simproptalk2023_slides.pdf

15:00 → 15:30 Discussion: UHECRs

15:30 → 16:00 Coffee Break

16:00 → 17:00 Scientific Session

16:00 Hadronic Interactions in CRPropa

The most relevant energy loss channel for Galactic Cosmic rays (GCRs) are the interactions with the ambient gas called hadronic interactions (HI). These interactions produce gamma-rays in the very high energy band as well as neutrinos and secondary leptons, hence establishing a connection between these messengers as observed on Earth. This is especially relevant with the recent observation of the Milky Way in high energy neutrinos where the multi messenger modelling of GCRs provides a more complete picture.

In this talk the implementation of HI for primary protons on a proton target, based on different parametrisations of the production cross-section, is presented. We apply different interaction models to simulate the interactions of GCRs with giant local molecular clouds and compare the results of the parametrised models to directly interfaced event generators.

Speaker: Julien Dörner (TP IV RUB)

Doerner_HadronicInteraction.pdf

16:30 Simulating UHECR sources with CRPropa using updated interaction modules

The study of the origin of Ultra-High-Energy Cosmic Rays (UHECRs) involves understanding how they interact and escape the sources. The escape is determined by the magnetic fields and the acceleration at the source, whereas the composition is affected by interactions which also lead to very high energy photons and neutrinos. CRPropa is well suited for studying these scenarios with the addition of dedicated modules. Two additional modules are discussed in this contribution: the recently developed Hadronic Interaction Module (HIM) which equips CRPropa with an additional means of handling hadronic interactions; and the Photohadronic Module (PHM) which implements an improved photomeson model previously published. The physical implications of these new additions are shown in the context of CRPropa simulations relevant to UHECR sources.

Speaker: Leonel Morejon

CRPropa Meeting 25.09.2023.pdf

17:00 → 17:30 Discussion: Hadronic Interactions

Tuesday, 26 September

09:00 → 10:30 Scientific Session

09:00 Time dependent particle injection to investigate the local source behaviour of flaring AGN

Since their discovery over a century ago, the origin of cosmic rays of the highest energies is still widely uncertain. A promising class of potential sources are Active Galactic Nuclei (AGN), that appear in quiescent and flaring states. To numerically modelate their local-source behaviour in detail, in foregoing work the software CRPropa was extended, to be able to capture the jet-physics on local scales, propagating a relativistic plasma blob along a jet axis. The goal of this work is trying to further extend this model accounting for a temporal variability of the source. For this purpose, a new source feature was introduced, allowing for a time dependent particle injection and therefore the finite lifetime of sources. Using a Monte-Carlo-Sampling approach, different luminosity profiles can be realized. In a next step, it is planned trying to modelate with this framework the multimessenger signatures of flaring AGN sources.

Speaker: Mr Leander Schlegel (Ruhr-Universität Bochum)

LS_CRPropa Meeting 25.09.2023.pdf

09:30 Synchrotron radiation in CRPropa

Speakers: Athithya Aravinthan, Jonas Hellrung, Julien Dörner (TP IV RUB), Lukas Merten

Synchrotron Module CRPropa 3.2 - 26.09.2023.pdf

10:00 On numerical Simulations of Intergalactic Electromagnetic Cascades with Lorentz Invariance Violation Using CRPropa

Lorentz invariance violation (LIV) is a proposed phenomenon where Lorentz symmetry is violated at high energies, potentially affecting particle dynamics and interactions. We use numerical simulations with the CRPropa framework to investigate LIV in gamma-ray-induced electromagnetic cascades, specifically studying how it impacts cascading electrons and photons undergoing pair production and inverse Compton scattering. Our detailed analysis of the simulation results, compared with existing theoretical models, reveals that LIV can significantly alter the behavior of both components of the cascade, photons and electrons, resulting in specific signatures in measured fluxes that could be observed in high-energy gamma-ray observations. These insights are crucial for ongoing searches for LIV and for the development of theoretical models incorporating LIV effects.

Speaker: Andrey Saveliev

Saveliev_CRPropa.pdf

10:30 → 11:00 Coffee Break

11:00 → 12:00 Scientific Session

11:00 Coupling axion-like particles to photons during propagation: the ALPinist plug-in

Axion-like particles (ALPs) are hypothetical entities often invoked to solve various problems in particle physics and cosmology. They are one of the most promising candidates to explain the elusive dark matter. A way to search for ALPs is through their effects on photons. In the presence of external magnetic fields, ALPs and photons can convert into one another, leading to measurable signals. Here we present results of Monte Carlo simulations of ALP-photon interconversion in magnetised environments using the ALPinist plug-in for the CRPropa framework. We illustrate its applications in the context of TeV gamma-ray propagation over cosmological distances.

Speaker: Rafael Alves Batista

RAB-20230926-CRPropa.pdf

11:30 Characterisation of gamma-ray propagation in our Galaxy

Motivated by recent observations of Galactic TeV gamma-ray sources and their uncertain origins, we investigate the propagation of gamma rays in our Galaxy.
TeV and PeV gamma rays produce electron-positron pairs over Galactic length scales due to interactions with background radiation fields, i.e. Cosmic Microwave Background (CMB) and Intra Stellar Radiation Field (ISRF). The highly energetic charged particles are deflected by the Galactic Magnetic Field (GMF) and, in turn, they might scatter background photons up to several TeVs, the well-known inverse Compton process. These processes trigger lectromagnetic cascades, which can eventually be detected by an observer at Earth.
Employing the latest tools of CRPropa 3.2, we simulate the emission from sources located at different position in our Galaxy, trying to spot hints of extended emission and spectral features in dependence to the galactic environment properties (GMF and the spatial-dependent ISRF). We find that the combination of CMB and ISRF can affect the observables from Galactic gamma-ray sources.
The preliminary results will be presented concurrently with future perspectives and possible improvements to this work.

Speaker: Gaetano Di Marco

CRPropa23_GDiMarco_def.pdf

12:00 → 12:05 Conference Picture

12:05 → 14:00 Lunch Break

14:00 → 15:30 Scientific Session

14:00 Probing the intergalactic magnetic field through gamma-ray observations

The origin of magnetic fields in galaxies and clusters of galaxies are generally explained via amplification mechanisms of weak seed fields. However, the nature of these seeds is still unknown. Two different hypotheses exist: the astrophysical and the cosmological origins. In the latter case a residual magnetic field is expected in the cosmic voids. For this reason it is crucial to look for signatures of magnetization in regions devoid of structures.

A possible way to constrain the Intergalactic Magnetic Field (IGMF) is based on gamma ray observations of extragalactic sources. Very High Energy (VHE, E>100 GeV) photons from an extragalactic source interact with the intergalactic medium producing an electromagnetic cascade at lower energies. The presence of a not negligible IGMF induced observable effects in the cascade signal that can be used to measure or constrain the IGMF configuration. In this talk I review the most important results achieved in the last years and give a future perspective in the context of CTA (Cherenkov Telescope Array)

Speaker: Paolo Da Vela

IGMF_from_gamma.pdf

15:00 Very-high-energy gamma ray propagation with CRPropa, CRbeam and ELMAG

We asses the precision of the modeling of electromagnetic cascades using model calculations with publicly available Monte-Carlo codes CRPropa, CRbeam and ELMAG and compare their predictions with theoretical expectations. We find that model predictions of different codes differ by up to 50% for low-redshift sources, with discrepancies increasing up to order-of-magnitude level with the increasing source redshifts. We identify the origin of these discrepancies and demonstrate that after eliminating the inaccuracies found, the discrepancies between the three codes are reduced to 10% when modeling nearby sources with z~0.1. Our corrections were taken into account and implemented by developers of ELMAG and CRPropa in the new versions of their codes: CRPropa 3.2 and ELMAG 3.03. We argue that the CRbeam code provides reliable predictions for spectral, timing and imaging properties of the secondary gamma-ray signal for both nearby and distant sources with z~1. Finally, we use CRbeam and corrected CRPropa to set a lower bound on IGMF from time variability of 1ES 0229+200 and Fermi/LAT observations of the "pair echo" of GRB 221009A.

Speaker: Alexander Korochkin

korochkin_slides.pdf

15:30 → 16:00 Coffee Break

16:00 → 17:00 Scientific Session

16:00 Influence of plasma instabilities on the propagation and spectrum of extragalactic electromagnetic cascades

The role of plasma instabilities in the development of electromagnetic cascades from extragalactic sources has gained importance as an alternative theory that seeks to explain the deviation of observed photon flux results from theoretical predictions at the GeV scale. This phenomenon is the result of the interaction between electron-positron pairs with the intergalactic medium (IGM). The development of these instabilities could cool down the electron-positron pairs more efficiently
than the inverse Compton scattering, being a possible cause of the observed suppression in the photon flux. For this reason, we studied the impact of instabilities in electromagnetic cascades through a parametric study in computer simulations, performed with the Monte Carlo code CRPropa. We developed a new interaction module in CRPropa for electrons and positrons that accounts for the energy losses due to these instabilities. A numerical methodology was created for the study
of the photon spectrum at Earth generated in electromagnetic cascades, coming from a blazar emitting very-high energy gamma-rays (VHEGR) with a given emission spectrum. This framework was used to reconstruct the spectrum at Earth for specific blazar emission and parametrization of the plasma instabilities. The results suggest a non-negligible effect of instabilities for the suppression of GeV-photon flux for some plasma parameters and injected spectra. This approach could also be used to
reformulate the preexisting bounds on intergalactic magnetic field (IGMF).

Speaker: Luis Enrique Espinosa Castro

LuisEnriqueEspinosaCastro.pdf

16:30 Local Source Physics with CRPropa - Extending Test Particle Simulations for Modelling Leptohadronic AGN Jets

Active galactic nuclei (AGN) and the accompanying jets are candidates for the engine of ultra-high-energy cosmic rays, gamma rays, and neutrinos. In 2017, IceCube observed an extragalactic high-energy neutrino event with a strong hint of a directional coincidence with the position of a known jetted AGN TXS0506+056. A deep understanding of the processes related to jets will fuel the field of high-energy cosmic rays, fundamental plasma, astro, and particle physics. However, an AGN jet’s physical and mathematical modelling is challenging, with ambiguous signatures that need to be understood by numerical simulations of cosmic-ray transport and interactions.

In this context, we present a simulation framework based on CRPropa 3.1 for hadronic constituents and their interactions inside a plasmoid propagating along the AGN jet axis. Consequently, with the ability to fully resolve particle propagation in three spatial dimensions, the framework was utilised to investigate the impact of spacetime-dependent photonic and hadronic target fields on hadronic interactions. In addition, we discuss the time dependence of these interactions and the resulting secondary particle spectra from blazar jets. Furthermore, we will present the results of our simulations and discuss how to implement non-linear leptonic radiation processes into our test particle simulation framework, enabling us to construct an improved physical description of AGN jets with spatially and temporally resolved interactions inside them.

Speaker: Marcel Schroller

Slides_Schroller_Marcel_CRPRopa_WS.pdf

17:00 → 17:30 Discussion: Leptonic/gamma ray interactions

19:00 → 21:30 Coffee Break: Conference Dinner

Wednesday, 27 September

09:00 → 10:30 Scientific Session

09:00 Ensemble Averaged Transport with CRPropa

Ensemble averaged transport modelling has become one of the key ingredients in the CRPropa framework. It is nowadays used to describe the propagation of Galactic cosmic rays, simulate the spatial transport in sources or to test analytical predictions of particle acceleration.

CRPropa’s DiffusionSDE module was originally developed as a low energy extension of the existing ultra-high energy cosmic ray propagation code, focused on Galactic cosmic rays. This physics case strongly influenced the design of the implementation, which was optimized to describe anisotropic spatial diffusion in complicated coherent magnetic field models. However, the current structure of the DiffusionSDE module makes it difficult to allow for spatially varying Eigenvalues of the diffusion tensor or include momentum diffusion.

This contribution will discuss our ongoing work to generalize the solvers for stochastic differential equations, leading to more efficient simulations and allowing to solve more realistic transport equations. The new implementation will be demonstrated with examples for first and second order particle acceleration.

Speaker: Lukas Merten

20230927_CRPropa_SDE-Solver.pdf

09:30 Diffusion of Energetic Particles in Turbulent Magnetic Fields

Spatial and momentum diffusion are important transport processes for
energetic particles in various astrophysical environments. A lot has been
learned from studying the transport conditions in the heliosphere, where
in-situ measurements provide comparatively detailed insights. In the talk
different approaches to quantitatively describe these processes and how
to test the corresponding models will be discussed.

Speaker: Horst Fichtner

crpropa_all.pdf

10:00 Investigating Charged Particle Transport in Non-Gaussian Magnetic Turbulence Models

Quasilinear theory has dominated the description of charged particle transport in magnetic turbulence since the 1960s.
While it leads to important insights, one should keep in mind that it characterizes the turbulent magnetic field solely
by the power spectrum, which has lead to a wide range of models describing the magnetic field by a simple self-similar
random field with a prescribed two-point correlation structure.
That this is not sufficient for a more realistic model can be concluded from magneto-hydrodynamic (MHD) simulations and
solar wind observations that exhibit multifractal behaviour and coherent structures such as current sheets.
Recently, there has been an increased interest in the transport of charged particles in non-Gaussian random magnetic fields
as well as MHD fields, however the exact processes are not yet fully understood.
We investigate how certain features of such fields modify the transport behaviour by comparing test particle simulations in
simple self-similar random fields, unstructured multifractal random fields, a variant of the minimal multi-scale Lagrangian
mapping procedure, and full 3D MHD fields.
The statistics and the structures of the employed fields are studied via their structure functions and occurrence of different magnetic features including field line curvature.

Speaker: Frederic Effenberger

Effenberger_CRPropa_WS_2023.pdf

10:30 → 11:00 Coffee Break

11:00 → 12:00 Scientific Session

11:00 The Galactic diffuse gamma-ray and neutrino emission at the PeV frontier

The LHAASO collaboration recently reported a robust measurement of the diffuse gamma-ray emission from the Galactic plane at energies from $\sim10$~TeV up to the PeV. This observation represents a clear evidence of a higher diffuse gamma-ray flux from the Galaxy than the expected from traditional models of CR interactions.
On top of this, the recent detection of neutrinos from the Galactic plane by the IceCube collaboration show a similar excess with respect to previous estimations, which further supports a larger rate of hadronic interactions in the Galaxy that would explain both observations. However, the uncertainties in the contribution from sources are still too high to discard this as the origin of these excesses.

Here, we present updated comparisons of a model of inhomogeneous propagation of cosmic rays in the Galaxy that is tuned to reproduce the Fermi-LAT measurements across the Galactic plane in the GeV range. We show further proof that the predictions from this model reproduce the observed gamma-ray diffuse emission from few GeV up to the PeV, which indicate that these emissions are dominated by the emission from cosmic-ray interactions in the Galaxy.
Finally, we show how this model perfectly reproduces the measurements from LHAASO in the inner and outer parts of the Galactic plane, as well as the IceCube best-fit measurement.

Speaker: Pedro De la Torre Luque (Oskar Klein Centre, Stockholm University)

PedroDeLaTorre_CRPropaWorkshop.pdf

11:30 Modeling Superdiffusive Particle Transport with CRPropa3.2

In the heliosphere, power laws in space and time profiles of energetic particles are observed. It has been proposed that they result from superdiffusive transport. Such anomalous, non-Gaussian, transport regimes may arise as consequence of intermittent magnetic field structures.

Superdiffusive particle transport can be described by a space-fractional Fokker-Planck equation. Numerical solutions can be obtained by solving the corresponding Stochastic Differential Equation (SDE). In case of Gaussian diffusion, the SDE is driven by a normal distribution, for superdiffusion it is driven by a symmetric stable Lévy distribution.
We solve the fractional diffusion-advection equation with a modified version of CRPropa3.2 and obtain the time-dependent solution of the cosmic-ray density. Our simulations lead to results that are compatible with the expected power law particle distribution upstream of a shock. Furthermore, we compare the SDE approach to a Fourier series approximation of the solution to the space-fractional Fokker-Planck equation.

Speaker: Sophie Aerdker

Modeling_Superdiffusive_Particle_Transport.pdf

12:00 → 12:30 Discussion: Diffusion

12:30 → 14:00 Lunch Break

14:00 → 14:45 Scientific Session

14:00 The IMAGINE magnetic field library

The IMAGINE Consortium aims to coordinate and facilitate research in the broad areas of the interstellar medium (ISM), in particular the Galactic magnetic field and cosmic rays. Our goal is to develop more comprehensive insights into the structures and roles of interstellar magnetic fields and their interactions with cosmic rays. One of the backbones of the consortium is a model library, which aims to collect available parametric models of the Galactic magnetic field and related ISM fields and to cast them into a unified interface.
In my talk, I will give a short overview over this library and discuss its current and planned features. My goal is to gauge interest of the CRPropa community in this library and to discuss possible conceptual and technical requirements for interoperability of the two frameworks.

Speaker: Sebastian Hutschenreuter (University of Vienna)

SHutschenreuter.pdf

14:45 → 15:30 Discussion: The future of CRPropa

15:30 → 16:00 Coffee Break

16:00 → 17:00 Developer Meeting: Developer Meeting (closed)