Combined fit of the energy spectrum and mass composition across the ankle with the data measured at the Pierre Auger Observatory

Ultra-High-Energy Cosmic Rays: The Intersection of the Cosmic and Energy Frontiers

“…It could be the signature of propagation effects in a single (intermediate nuclei) extragalactic component, or a cross-over region between two extragalactic source populations. Notably, a combined fit of Auger measurements of the UHECR energy spectrum and composition across the ankle seems to suggest the presence of two extragalactic components, though an intermediate-mass galactic component might also be present below the ankle [106]. The secondary neutrino and gamma-ray fluxes expected in these scenarios, for each source population model, will provide concrete constraints.…”

“…The shape is thus an object of detailed scrutiny for studying the combined effects of the evolution of the arrival directions and mass composition with primary energy. The precise measurements of the spectrum have been used to put strong constraints on astrophysical models of the sources, particularly when combined with other measurements like X max [106,107] (see Ch. 4).…”

Extragalactic cosmic rays

“…In order to obtain a clean separation of the mass groups, a very hard slope of the injection spectrum into extragalactic space is required: For instance, the fits presented in Ref. [14] use slopes for 𝑑𝑁/𝑑𝐸 ∝ 𝐸 −𝛼 with 𝛼 between −1 and −2. Moreover, the ankle has to be explained by a second extragalactic population which does not show the same Peters cycle but has a dominantly light composition.…”

Constraining ultra-high-energy cosmic ray composition through cross-correlations

“…In order to be able to treat this problem analytically we conservatively smear uniformly across the sky with the maximum value of σ, obtained from b = 0; this gives a displacement of approximately 4.7 deg for 40 EeV protons. 5 Because the magnetic deflections depend not only on Z but also on the energy, we can improve on the analysis by binning the UHECR flux in five logarithmic energy bins with logarithmic width of 0.1, and compute the total flux by adding them up proportionally to the UHECR energy spectrum (see below)-we do this for each UHECR species separately. The kernel Equation 2.3 is generalised as…”

“…More precisely, we know that these UHECRs are charged nuclei-neutral particles can make up only a marginal fraction of the detected UHECR flux at the highest energies (see e.g. [3])-but direct measurements of the UHECR atomic number(s) Z (i.e., their chemical composition) are, to this day, inconclusive [2,4,5]. This is because these measurements are prone to systematics (e.g.…”