CRPropa

CRPropa is a numerical framework developped mostly at the APC, and whose goal is to simulate the propagation of UHECRs and their secondaries on large distances. It has been conceived in order to interpret the expected flow of data from UHECR experiments (in particular Auger), as well as neutrino and VHE astronomy. It can follow the propagation of cosmic nucleons in magnetic fields, their interactions on photon backgrounds, and the propagation of secondary neutrinos and electromagnetic cascades.

Presentation and physical motivations

To understand the origin of ultra-high energy cosmic rays (UHECRs), it is required to modelize in a realistic way their propagation in the Universe. UHECRs can interact with low energy radio, microwave, infrared and optical photons to produce electron/positron pairs or pions. The latter decay and give rise to neutrinos and electromagnetic cascades extending down to MeV energies. In addition, deflections in cosmic magnetic fields can influence the spectrum and sky distribution of primary cosmic rays and, due to the increased propagation path length, the secondary neutrino and gamma-ray fluxes. Neutrino, gamma-ray, cosmic ray physics and extra-galactic magnetic fields are, therefore, strongly linked subjects and should be considered together to extract maximal information from existing and future data, like the one expected from the Auger Observatory. For that purpose, we have developed CRPropa, a publicly-available numerical package which takes into account interactions and deflections of primary UHECRs as well as propagation of secondary electromagnetic cascades and neutrinos. CRPropa allows to compute the observable properties of UHECRs and their secondaries in a variety of models for the sources and propagation of these particles. CRPropa inherits from various codes that have been previously developped: a Fortran code for the propagation in magnetic fields, by M. Lemoine and G. Sigl; a C code for the development of electromagnetic cascade, by S. Lee; and the public SOPHIA event generator for pion production.

General structure of the framework

Simple examples of simulations

We present here simple examples of configuration files that allow to simulate some basic physical effects. These configuration files can also play the role of standard tests of the code (these are only quick simulations). The configuration files are made of xml markers and are quite intuitive, so that you can imagine what is happening for each simulation by reading these files. The output (in ASCII or FITS) are arrays of "events" or "trajectories", which you can use with your favorite data processing utility to produce various results (the plots presented here are made with IDL).

Documentation and download

The following documentation is available:

A paper accompanying the package. Please cite this paper (Astropart. Phys. 28, 463-471, astro-ph/0603675) if you use the code. Accompanying paper (.pdf)
The current user guide in pdf
The internship report by Sébastien Renaux-Petel in ps (in french), which provides examples of use of the code in the framework of GZK neutrino studies and technical details on the "reweighting" method which is useful for simulations.

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Authors

Eric Armengaud

Tristan Beau

Günter Sigl

We acknowledge various people for many helps and the development of former cosmic ray propagation codes from which this package is inspired: Cyril Lachaud, Sébastien Renaux-Petel, Martin Lemoine, Gianfranco Bertone, Claudia Isola, Sangiin Lee.

We use the packages SOPHIA (Mücke et al., Comput. Phys. Commun. 124, 290), TinyXML, CLHEP and CFITSIO.