O-15 - Auger combined spectrum from 310,000 events - ankle 5.1 EeV, instep 13 EeV above 5.5 sigma, suppression 48 EeV
The dominant systematic is the 14% absolute energy-scale uncertainty common to all Auger flux results (calorimetric fluorescence calibration); bin-to-bin flux correlations from it are 0.75-0.99 (Table VI). Combined-spectrum normalization J0 = 1.271 +/- 0.004 km^-2 sr^-1 yr^-1 EeV^-1 with indices gamma1 = 3.26, gamma2 = 2.51, gamma3 = 2.99 (Table I).
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Combined vertical and inclined surface-detector spectrum from the Pierre Auger Observatory, 2004-2022: ~310,000 events above 2.5 EeV, exposure 104,900 +/- 3,100 km^2 sr yr — the largest UHECR exposure to date. Energy scale set calorimetrically by the fluorescence detector; dominant systematic the 14% absolute energy-scale uncertainty, inducing bin-to-bin flux correlations of 0.75-0.99 (Table VI). Declination dependence tested by measuring spectra in five declination bands spanning -90 to +44.8 deg; feature significances from a test statistic over 10^8 Monte Carlo realizations, robust under +/-14% energy-scale shifts.
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Why this is evidence
The instep is the discriminator: H-12 predicts a feature between ankle and suppression from the crossover of helium and CNO components, while a pure extragalactic-proton spectrum (H-9) and a Galactic-to-extragalactic transition (H-21) predict a featureless power law there. The instep’s establishment above 5.5 sigma is expected under H-12 and surprising under H-9 and H-21.