A large part of the work done in the "UHECR analysis tool" Work Package concerns the “Combined fit”, a tool which evaluates
an astrophysical model aiming at describing the composition and the energy spectrum of
Ultra High Energy Cosmic Rays (UHECR). Nuclei are injected at sources, propagated through
the universe, and the obtained flux spectrum and composition are compared with observed
one to get the best fit scenario. A code has been developed by Antonio Condorelli (IJCLab),
in collaboration with Johan Bregeon (LPSC) and Sullivan Marafico (IJCLab), to perform
the Combined fit, and is available inside the team, with a version being prepared to be
delivered as a public tool. To deal with the propagation of nuclei, a tensor formalism has
been designed by Jonathan Biteau.
Antonio Condorelli and Leonel Morejon (BUW) have initiated a systematic comparison of
tensors obtained with the two main UHECR propagation codes (SimProp and CRPropa).
Combined-fit analysis including moments of log A, where A is the nuclear mass, moments
of Xmax, where Xmax is the mean shower depth, of Xmax distributions have been compared
by Antonio Condorelli, suggesting similar discrimination power although with known
differences in goodness-of-fit estimators. Carla Bleve (LPSC) and Corinne Bérat (LPSC)
are developing a module to account as well for mass observables from the surface detectors
of UHECR observatories.
A beta version of the combined fit including arrival directions has been developed by
Sullivan Marafico, Jonathan Biteau and Olivier Deligny (IJCLab). It will be integrated in
the main software by Sullivan Marafico by the end of 2022. In this beta version, transient
sources follow the distribution of stellar mass and star formation rate as traced by a
recent catalogue of ~400,000 galaxies within a billion lightyears (z~0.08) established by
Jonathan Biteau. The source evolution at larger redshifts follows the cosmic evolution of
these two tracers as inferred from deep-field observations. The best-fit model confirms
earlier findings of the IJCLab group. The magnetic field of clusters should strongly impact
UHECR skymaps. A collaboration between Antonio Condorelli and Remy Adam (LLR), has been
established to account for hadronic interactions and magnetic effects on UHECRs in galaxy
clusters. A publication is planned to be submitted by the end of 2022.
The partners from Bochum and Wuppertal Universities optimized and extended the CRPropa
framework. The new version CRPropa 3.2 (published in Sept 2022 in JCAP) received a major
upgrade as compared to the previously published version CRPropa 3.1. In v3.1, the concept
of diffusive propagation had been added by adding the solver for stochastic differential
equation as an alternative to the solution to the equation of motion. This opens the window
to not only using CRPropa as a tool for extragalactic propagation, but generally allows
for propagation in local and Galactic environments. To be able to do this, however, major
changes were needed. Most importantly, the photon fields relevant for extragalactic
propagation were hard-coded into the software. In a larger effort, the Bochum group
modified the program to be able to deal with custom photon fields. Further additions
led in Bochum were updates to the gas density and magnetic field modules. Further,
proton-proton interactions were added in a simplified approach as a first-order
approximation, only containing the pion and kaon contributions and only working for
large statistics samples. The development of a hadronic interaction module in CRPropa
is lead by the team in Wuppertal.
The development of a new propagation tool AGNPropa has made significant progress. Based on
the CRPropa code, the Bochum team develop the code AGNPropa with the aim to describe AGN
flares in the time, energy and ultimately also the spatial regime. A first working version
of the code exists, where it is possible to model the evolution of instantaneously injected
flares from blazars. A relativistic moving blob is simulated to contain a population of
high-energy cosmic rays that propagate in a magnetic field (so far to be assumed purely
turbulent, a regular field is to be added at a later stage). The blob is moving away from
the coronal radiation field of an AGN disk and photohadronic interactions with the disk
are included. A first performance test shows that gamma-ray absorption is working well.
The partners have further studied the performance of the code with the equation of motion
as compared to the transport equation approach and can show that the codes produce the
same results within numerical errors in the energy range where they both work. This is the
first type of code that can perform three-dimensional transport modeling. It is the goal
to compare this code to the transport codes on the market as a next step. To do so, the
German partners are currently implementing a synchrotron self Compton model, which is
technically challenging, as it is a non-linear process.
The activities in Wuppertal concerns firstly the
implementation of Hadronic Interactions in CRPropa: CRPropa has been equipped with a
module for hadronic interactions which takes input from a variety of existing hadronic
interaction codes (e.g. EPOSLHC, Sybill, QGSJet, and others). The module extends
CRPropa's region of applicability to environments such as bursting sources which
are of interest for this project. Testing of the module's performance and functionality
has been also carried out. A publication is in preparation showcasing it's usage
and presenting the physical predictions of the model in scenarios compatible with
bursting sources. It should be pointed out that the module is also intended for
galactic propagation of lower energy cosmic rays and other scenarios where ballistic
propagation is applicable and hadronic interactions are of relevance.
The BUW team contributes to the propagation framework and related tools in
collaboration with IJCLab. On the BU Wuppertal side, a propagation tensor produced
with simulations from CRPropa has been completed, as an alternative to the on produced
with SimProp in IJCLab. The advantage of such tensors is to allow faster evaluation
of multiple propagation scenarios such as different source distributions and all
possible nuclear compositions of nuclei up to the mass of Iron. Furthermore, an
additional deliverable, the propagation matrix, has been produced as separate
instrument for evaluation of cases where the redshift distribution does not change,
while changes of composition are studied. Furthermore, the propagation matrix is
comparable to previous published results and allows comparison of the current
tensor to those earlier works. The next steps include characterizing the tensors
by comparing them, and employ them in studies of UHECRs propagation.
A website with modern design has been prepared (BUW) and published on the web
to establish an online presence and communicate the progress of the project.
In addition, a logo has been designed and made available in the website for
presentation and download, with the intention of establishing a memorable visual
identity that is coherent over all forms of presentation of the work (slides, webpages, etc.).
The website acknowledges the funding parties, lists the scientists working for
the project, keeps a growing list of references to publications, contributions in
conferences and links to the software and tools produced in the project.
