# Progress towards characterizing ultrahigh energy cosmic ray sources

## TL;DR

This paper advances understanding of ultrahigh energy cosmic ray sources by integrating cosmic ray, neutrino, and gamma-ray data to constrain source models, composition, and evolution, revealing potential two-component cosmic ray models.

## Contribution

It extends the UFA15 model by exploring source evolution, photon field temperature constraints, and the possibility of a mixed or two-component cosmic ray composition.

## Key findings

- Good fit with narrow nuclear mass range or Milky Way-like composition
- Nearest source should be 30-50 Mpc for Milky Way-like composition
- Two-component model improves fit and aligns with multimessenger data

## Abstract

We use a multimessenger approach to constrain realistic mixed composition models of ultrahigh energy cosmic ray sources using the latest cosmic ray, neutrino, and gamma-ray data. We build on the successful Unger-Farrar-Anchordoqui 2015 (UFA15) model which explains the shape of the spectrum and its complex composition evolution via photodisintegration of accelerated nuclei in the photon field surrounding the source. We explore the constraints which can currently be placed on the redshift evolution of sources and the temperature of the photon field surrounding the sources. We show that a good fit is obtained to all data either with a source which accelerates a narrow range of nuclear masses or a Milky Way-like mix of nuclear compositions, but in the latter case the nearest source should be 30-50 Mpc away from the Milky Way in order to fit observations from the Pierre Auger Observatory. We also ask whether the data allow for a subdominant purely protonic component at UHE in addition to the primary UFA15 mixed composition component. We find that such a two-component model can significantly improve the fit to cosmic ray data while being compatible with current multimessenger data.