Multi-messenger Research on Cosmic Ray Origins


Keep track of the progress of the project.
Here we communicate the latest results and milestones achieved.


The origin of Ultra-High-Energy Cosmic Rays (UHECR) is still an open question despite the strong progress of research over the past 10-20 years. Taking advantage of the newly available high-statistics and high-quality data, most prominently obtained by the Pierre Auger Observatory, MICRO aims at identifying source classes that correlate best with existing observational UHECR data (direction, energy distribution, and primary mass).

A novelty of our multi-messenger approach will be a complete study of bursting sources starting from the modeling of selected source classes, including hadronic interactions within the source and over the propagation down to Earth, to predict the UHECR sky as a function of energy and primary mass.

Confinement constraints

Hillas diagram sorts source classes according to their potential for particle acceleration. The regions stem from the ranges of size, R, and magnetic field strength, B, characteristic of the source class of corresponding color. The product, BR, indicated with solid and dashed lines, represents the limits of confinement of protons (red) and iron (blue) nuclei with energy 100 EeV.are possible for outflows with values of β. This illustrates that multiple source classes have potential to accelerate UHECRs.

Source: A.Batista et al. Astron. Space Sci., Vol. 6, 2019

Luminosity - density

The rate of cosmic ray emission for a source class is governed by both the typical luminosity and the number density. Luminous sources with a lower density can have a combined output comparable to waker sources having a correspondingly higher density. The colored regions in the figure represent source classes with properties limited by the values of the regions' limits. For transient source, the effective luminosity assumes a characteristic time spread of 415 years. The black lines represent different total luminosities that can explain the UHECR energy production (5 × 1044 erg Mpc-3 yr-1). The gray horizontal shows the estimated lower limit to the UHECR source number density.

Source: A.Batista et al. Astron. Space Sci., Vol. 6, 2019

Multiple messengers

The observed fluxes of photons (blue data points) neutrinos (orange data points) and UHECRs (gray data points) are connected through particle interactions. Complex modelling is needed to understand these connections and to provide a common explaination for all messengers. Cosmogenic photon (blue) and neutrino (orange) fluxes were obtained with models that fit the Auger data including spectrum and composition (Alves Batista et al., 2019).

Source: A.Batista et al. Astron. Space Sci., Vol. 6, 2019


MICRO is an international project within the framework of French-German collaboration for research in Natural, Life and Engineering Sciences.The main goal is to understand the origins of Ultra-High Energy Cosmic Rays by using state-of-the-art methods in the field.
By improving the simulation tools, as well as combining experimental data and simulations, we expect to expand the knowledge regarding UHECR origins, the phenomena that produce them, and their connection with other messenger particles like gamma rays and neutrinos.
This project involves multiple scientists from several universities and research centers in France and Germany.


Head Researchers

Experienced Researchers

Postdocs and PhDs