Unmasking the ultrahigh-energy cosmic ray origin

Understand

The sharp change in slope of the ultrahigh-energy cosmic ray spectrum around 10^{9.6} GeV (the ankle), combined with evidence of a light but extragalactic component near and below the ankle which evolves to intermediate/heavy composition above, has proved exceedingly challenging to understand theoretically.

• Recently, we introduced a very general model in which, for a range of source conditions, photo-disintegration of ultrahigh-energy nuclei in the region surrounding the accelerator naturally accounts for the observed spectrum and composition of the entire extragalactic component, which dominates above about 10^{8.5} GeV.
• In this communication we review the generalities of the model and show that starburst galaxies provide a compelling source example.