CRPropa Workshop on Astroparticle Propagation

Instituto de Física Teórica UAM-CSIC

Instituto de Física Teórica UAM-CSIC

Universidad Autónoma de Madrid Campus de Cantoblanco C/ Nicolás Cabrera 13-15 28049 Madrid Spain
Rafael Alves Batista (Instituto de Física Teórica, Universidad Autónoma de Madrid (IFT UAM-CSIC))

The landscape of high- and ultra-high-energy astrophysics has changed in the last decade, in large part owing to the inflow of high-quality data collected by present cosmic-ray, gamma-ray, and neutrino observatories. At the dawn of the multimessenger era, the interpretation of these observations within a consistent framework is important to elucidate the open questions in this field.

The "CRPropa Workshop on Astroparticle Propagation" will cover topics related to the propagation of high-energy cosmic messengers, namely cosmic rays, electrons, gamma rays, and neutrinos, from GeV up to ZeV energies. With this workshop we intend to bring together users and developers of CRPropa, and to foster interactions amongst the different communities that make use of it. Its main goals is to discuss recent computational developments related to (but not restricted to) the  code, and more generally, in the theory of astroparticle transport in astrophysical environments and over cosmological distances. We will also have a dedicated discussion session highlighting the synergies with searches of physics beyond the Standard Model.

There will be ample time for discussions and for interactions among the participants, with the goal of promoting new collaborations. Participants who wish to extend their stay by a few days and use the opportunity to work together are welcome do so if arrangements are made well in advance.

The deadline for registration is August 15 August 28.


* All participants must comply with the COVID regulations imposed by the Spanish government at the time of the workshop.


Scientific Organising Committee

  • Rafael Alves Batista (chair)
  • Julia Becker Tjus
  • Karl-Heinz Kampert
  • Lukas Merten
  • Günter Sigl

Local Organising Committee

  • Rafael Alves Batista
  • Mónica Vergel
  • Alberto Saldana-Lopez
  • Alex Kääpä
  • Andrey Saveliev
  • Athy Aravinthan
  • Brandon Khan Cantlay
  • Claire Guepin
  • cynthia ventura
  • Dimitris Kantzas
  • Janning Meinert
  • Jaume Zuriaga Puig
  • Josina Schulte
  • Julien Dörner
  • Jurek Völp
  • Karl-Heinz Kampert
  • Leonel Morejon
  • Lili Yang
  • Lukas Merten
  • Miguel Sánchez-Conde
  • Nicole Araneda Muñoz
  • Prantik Sarmah
  • Quanbu Gou
  • Rafael Alves Batista
  • Silvia Salvatore
  • Simone Rossoni
  • Sophie Aerdker
  • Teresa Bister
  • Vasundhara Shaw
  • Viviana Gammaldi
  • Vladimir Kiselev
  • Xavier Rodrigues
    • 10:00 11:00
      Registration & Coffee 1h
    • 11:00 11:30
      Contributed Talks: Introduction IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

      • 11:00
        CRPropa Workshop: opening and introduction 30m
        Speaker: Rafael Alves Batista (Instituto de Física Teórica, Universidad Autónoma de Madrid (IFT UAM-CSIC))
    • 11:30 12:30
      Invited Talks: Multimessenger Astrophysics IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

      • 11:30
        High-energy particles from astrophysical transients 1h

        Decisive advances in the understanding of explosive transients have been made possible by the development of multi-messenger astronomy and time-domain astronomy. However, the origin of high-energy (HE) to ultra-high-energy (UHE) cosmic rays and neutrinos remain unclear. Deciding between the various source candidates requires a precise modeling of the propagation, acceleration and interactions of cosmic rays, and the subsequent multi-messenger and time-dependent emissions. We will describe the production of HE to UHE particles in the vicinity of transient sources, and highlight some key aspects related to the treatment of multi-messenger predictions, time-dependencies and uncertainties.

        Speaker: Claire Guepin (University of Maryland, NASA GSFC, University of Chicago)
    • 14:30 15:45
      Contributed Talks: Ultra-High-Energy Cosmic Rays IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

      • 14:30
        Fitting an astrophysical model for the UHECR origin 45m

        Three observables of ultra-high-energy cosmic rays can be measured with present-day observatories: the energy spectrum, the distribution of maximum shower depths and the arrival directions. We use all three observables for a combined fit, in which the parameters of possible UHECR sources are constrained. The astrophysical model used in this fit is based on 1-dimensional CRPropa3 simulations, taking into account all known interactions. Then, these 1-dimensional simulations are reweighted to account for the three-dimensional source setup consisting of homogeneous background sources and a variable contribution from nearby source candidates. The signal fraction, as well as the size of a rigidity-dependent local magnetic field blurring, are part of the fit parameters. The influence of the extragalactic magnetic field is investigated, considering the low-energy suppression due to diffusion, as well as a source-distance-dependent beam-widening of the arrival directions.

        Speaker: Teresa Bister (RWTH Aachen University)
      • 15:15
        Inverting UHECR propagation with a normalizing flow 30m

        As shown by the Pierre Auger Collaboration, the combined fit of energy spectrum and depth of shower maximum distributions of ultra-high-energy cosmic rays can provide constraints on the parameters their sources. To this end, a database describing the connection between the shape of the injected energy spectrum and composition at the sources and the observables measured on Earth is built using 1-dimensional CRPropa3 simulations. Here, the injection at the source is described by several free model parameters, namely the spectral index, maximum rigidity and five representative mass fractions.The inference of the free model parameters can be done with, e.g., Markov chain Monte Carlo (MCMC) sampling which allows to reconstruct posterior distributions.
        In this work, we investigate an alternative approach based on normalizing flows, a conditional invertible neural network. We show that the posterior distributions obtained with the network agree with those using MCMC, for a simulation of energy spectrum and shower depth distributions resembling Auger measurements. Additionally, the mapping of the source parameters and the observables as learned by the cINN is investigated. The accuracy of the reconstructed variables on a test dataset is shown to be very good. For different applications, the concept may also be exploited to swiftly generate observables for specific source scenarios after the initial computing-expensive learning phase.

        Speaker: Josina Schulte (RWTH Aachen University)
    • 15:45 16:15
      Coffee break 30m
    • 16:15 17:15
      Invited Talks: Ultra-High-Energy Cosmic Rays IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

      • 16:15
        Efficient UHECR simulations with PriNCe and what they taught us so far 1h

        In this talk I will introduce PriNCe (Heinze et al 2019) as a novel open-source Python software for UHECR propagation. The computational efficiency of PriNCe allows the user to perform vast scans of the source parameters, the emitted spectral shape, and the mass composition. I then discuss recent applications of the code, such as the first joint fit to Auger and Telescope Array (TA) spectral and composition data. The fit favors the presence of a local source of UHECRs in the Northern Hemisphere at the 5.6$\sigma$ level compared to the scenario where both experiments observe only an isotropic source population. I comment on possible source candidates based on the predicted distance and mass composition.

        Speaker: Xavier Rodrigues (Ruhr University Bochum)
    • 17:15 18:00
      Discussions IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

    • 09:30 10:45
      Contributed Talks: Cosmic Rays: from extragalactic to Galactic IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

      • 09:30
        CRPropa high statistic simulations for UHECR anisotropy studies 40m

        Despite the great progress made by modern cosmic ray observatories, the origin and acceleration mechanism of ultra-high-energy cosmic rays (UHECRs) remains an unsolved problem to this day. However, there is experimental evidence for an anisotropic component in the UHECR arrival direction greater then few EeV. The search for UHECR sources is further complicated by two main factors: during extragalactic propagation UHECRs interact with background photon fields (like the CMB and the EBL) and, since they are electrically charged, they are deflected by extragalactic and galactic magnetic fields (EGMF and GMF). Moreover, the strength, structure and origin of the EGMF are still not well known, causing reconstructing the deflection of UHECRs a non-trivial task. In this work we consider several EGMF models obtained from constrained MagnetoHydroDynamics (MHD) simulations of our local Universe to study the propagation of UHECRs through such a structured environment. We simulate propagation, interactions and observation of UHECRs by using the Monte Carlo code CRPropa3. We also take into account the effect of the GMF by adopting a lensing procedure of the arrival UHECR sky map. We explore several combination of source distribution, EGMF structure and mass composition. As a reference, we also simulate scenarios without the EGMF and with a statistically homogeneous field. We use our simulation results to compute UHECR observables, such as the energy spectrum, the angular power spectrum and the arrival direction map (before and after the GMF) in order to obtain constraints on possible combinations of source distributions and EGMF models.

        Speaker: Mr. Simone Rossoni (University of Hamburg)
      • 10:10
        Neutrinos and gamma rays from clusters of galaxies 35m

        Cosmic rays can be accelerated to high energies by astrophysical objects embedded in clusters of galaxies or by shocks taking place in the intracluster medium. These cosmic rays are trapped within clusters, interacting with the gas and radiation permeating this environment, producing high-energy non-thermal messengers including neutrinos and gamma rays. These messengers can be observed either from individual clusters or as diffuse fluxes resulting from the whole population of these objects. While their fluxes depend on properties of the cosmic-ray emission, this contribution is guaranteed to exist, consequently constraining the parameter space available for other components that could generate them, such as some populations of astrophysical objects and the elusive dark matter. In this talk I will describe the propagation of high-energy cosmic rays in galaxy clusters considering a sample of these objects obtained from cosmological magnetohydrodynamical simulations of structure formation. I will then present estimates for the neutrino and gamma-ray fluxes from individual clusters, followed by estimates of the associated diffuse neutrino and gamma-ray fluxes. Finally, I will discuss these results within a broader astrophysical context, focusing on their importance for high-energy multi-messenger astronomy.

        Speaker: Rafael Alves Batista (Instituto de Física Teórica, Universidad Autónoma de Madrid (IFT UAM-CSIC))
    • 10:45 11:15
      Coffee break 30m
    • 11:15 12:45
      Contributed Talks: Astroparticle Propagation in Various Astrophysical Environments IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

      • 11:15
        Inferring the diffusion coefficient in the heliosheath by time spectra simulations of GCRs in the HelMod framework 30m

        The cosmic rays propagation inside the heliosphere is a very complex physical process, well described by the Parker Transport Equation (PTE). When travelling in the heliosphere, particles undergo convection, diffusion and energy changes as they move in the irregular magnetic fields originated from the Sun, and their flux is therefore modulated. The irregularities are due to the outward flowing solar wind plasma, incapsulating the interplanetary magnetic field within the heliopause. HelMod is a code developed in INFN and Università di Milano-Bicocca solving the PTE in terms of stochastic differential equations and returning the modulated energy spectrum of the particles inside the heliosphere. The extremely turbulent region from the termination shock to the heliopause – the heliosheath - is responsible for a significant part of the modulation, particularly for low energy CRs. In this work, the solar modulation for H, He, C, O, Mg and Si ions is studied in the 2000-2016 time period and compared with the Voyager 1 data, in a ~ 0.5 - 2 GV rigidity range. This procedure allows us to infer the diffusion coefficient function inside the heliosheath area, i.e. a power law with γ=1.4.

        Speaker: Silvia Salvatore
      • 11:45
        Cosmic Ray Electron transport in the external galaxy M51 30m

        Recent measurements of the synchrortron emission of the external galaxy M51 give indirect implication for the cosmic-ray electron (CRE) transport in the interstellar medium.
        By modelling the CRE transport considering all relevant energy loss processes we aim to distinguish the contribution of diffusive and advective transport. The current measurements give insights in the diffusion coefficient, the star formation rate and the magnetic field strength.
        Using these information we use the CRPropa module DiffusionSDE to solve the 3D transport equation for isotropic diffusion and the 3D-advection profile. Additionally we implement the relevant energy loss processes as a continues loss.

        With our best fit model the data can be described well. For the best fit the wind speed followed from the observation of the star formation rate must be decreased by a factor 5. We find that the inner galaxy is dominated by advection and the outer by spatial diffusion.

        In general leads this approach of modelling face-on galaxies insights of the only indirect observable advection profile.

        Speaker: Julien Dörner (Ruhr-University Bochum)
      • 12:15
        Galactic propagation of GCRs and EGCRs in the shin region with CRPropa 30m

        The energy range pertaining to the shin region of the cosmic ray (CR) energy spectrum is noteworthy in that propagation shifts from diffusive to ballistic with increasing energy. At the same time, the transition from Galactic cosmic rays (GCRs) to extragalactic cosmic rays (EGCRs) in this energy range, the details of which hitherto not certain.

        This talk details the approach I employed in the study of the propagation effects of the GMF on GCRs and EGCRs. We begin with a brief comparison of the two numerical approaches utilisable in this energy range (the Transport Equation approach and the Equation of Motion approach), followed by an outline of the simulation setup and a brief discussion of necessary considerations pertaining to it. After this, the arising propagation effects are presented, along with their effects on CR observables, and finally the physical implications for the shin region are drawn.

        Speaker: Alex Kääpä (Ruhr Universität Bochum)
    • 14:45 15:45
      Invited Talks: High-Energy Gamma Rays IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

      • 14:45
        Gamma-ray attenuation from extragalactic background light in the Fermi and CTA era 1h

        The diffuse extragalactic background light (EBL) is formed by ultraviolet (UV), optical, and infrared (IR) photons mainly produced by star formation processes over the history of the Universe and contains essential information about galaxy evolution and cosmology. The EBL also attenuates gamma-ray fluxes that travel cosmological distances through pair-production interactions, leaving a signature in the gamma-ray spectra of extragalactic sources. In this talk, we present a new determination of the evolving EBL spectral energy distribution using a novel approach purely based on galaxy data aiming to reduce current uncertainties on the higher redshifts and IR intensities. Our results are based in one of the most comprehensive and deepest multi-wavelength galaxy datasets ever obtained, which allow us to derive the overall EBL evolution up to z~6 and its uncertainties. We will also discuss the gamma-ray optical depths that are obtained from our EBL approximation, and how we can measure galaxy evolution and other cosmological properties such as the cosmic star-formation rate and the expansion rate of the Universe using gamma-ray observations of blazars.

        Speaker: Alberto Saldana-Lopez (University of Geneva)
    • 15:45 16:15
      Coffee break 30m
    • 16:15 17:00
      Contributed Talks: High-Energy Gamma Rays IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

      • 16:15
        Deriving Constraints on Intergalactic Magnetic Fields 45m

        Intergalactic Magnetic Fields (IGMFs) are one of the most important phenomena in astrophysics and cosmology, as a lot of information concerning the evolution and the present state of the Universe may be derived using them. In order to put constraints on IGMFs, one needs to consider a variety of their interactions with different environments: On the one hand, they influence the propagation of charged particles, of which Ultra High Energy Cosmic Rays (UHECRs) and electromagnetic cascades initiated by TeV-gamma rays are of particular interest since their trajectories are highly sensitive to IGMF parameters (such as their average field strength, correlation length, spectrum and helicity). On the other hand, IGMFs directly interact with the Intergalactic Medium (IGM), the understanding of which requires numerical and (semi-)analytical large-scale simulations. In case one assumes that they have been created in the Early Universe, one has also to consider cosmological aspects such as their impact on the Cosmic Microwave Background (CMB), which might be used to derive further constraints. In this talk we will discuss all these different methods for a coherent and comprehensive view on IGMFs.

        Speaker: Andrey Saveliev
    • 17:00 18:00
      Discussions IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

    • 09:30 11:00
      Contributed Talks: CRPropa developments IFT, Sala Roja (red room)

      IFT, Sala Roja (red room)

      • 09:30
        Hadronic interactions with CRPropa 30m


        Speaker: Leonel Morejon (Wuppertal University)
      • 10:00
        Modelling Diffusive Shock Acceleration with CRPropa 30m

        Cosmic ray particles reach energies as high as $10^{21}\,$eV, and most likely they are accelerated in varying electromagnetic fields present in astrophysical sources and the interstellar medium. Most promising acceleration mechanisms are the First and Second Order Fermi acceleration: Cosmic ray particles repeatedly scatter on moving magnetic field turbulences and on average they gain energy from these collisions.
        I present how the First order mechanism, also referred to as Diffusive Shock Acceleration, can be modelled with CRPropa using the DiffusionSDE Module. Particles are accelerated when they diffuse over the shock and experience a changing flow velocity. Changes in the advective field and the diffusion coefficient over the shock are approximated by differentiable functions that can be handled by DiffusionSDE. With this approach, the resulting CR spectrum highly depends on the choice of the "shock width" and the step length of the simulation.
        In addition, I give an outlook how the Second order mechanism, also referred to as Momentum Diffusion, can be modelled by stochastic differential equations. The modelling of Diffusive Shock Acceleration and Momentum Diffusion extend CRPropa's Acceleration Module to diffusive transport.

        Speakers: Lukas Merten (Ruhr University Bochum) , Sophie Aerdker (Ruhr-University Bochum)
      • 10:30
        Momentum diffusion 30m
    • 11:00 11:30
      Coffee break 30m
    • 11:30 13:00
      Discussions: The Future of CRPropa: ideas, developments, and community input
    • 14:30 17:30
      CRPropa Core Team Meeting
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