Most precise Auger energy-spectrum measurement to date: ~310,000 events above 2.5 EeV from an exposure of ~104,900 km^2 sr yr, extending declination coverage and confirming the “instep” feature above 5 sigma. relevance_note: current best/most statistically powerful primary flux measurement; the up-to-date normalization for any “collisions absorbed by Earth over billions of years” calculation.
Methodology
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.
Results (§III-IV)
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).
Link to originalMethodology
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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O-16 - Auger energy spectra are declination-independent from -90 to +44.8 degrees apart from the known dipolar modulation
Region-specific checks: excluding or isolating the Centaurus-region overdensity (24-deg window around RA 201 deg, dec -43 deg) leaves the band spectra consistent within statistical fluctuations; the same holds around NGC 253 and NGC 1068.
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Discussion (§V)
H-12 - The instep and steepening reflect overlapping helium and CNO flux components with a narrow source rigidity maximum, not a few foreground sources
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A-16 - Declination-independence of the spectrum disfavors a few-source origin of the instep
Reasoning
- Different declination bands see different celestial regions; a spectral feature produced by a handful of localized sources (e.g. the Centaurus-region overdensity) would appear preferentially in the bands containing them, distorting those bands’ spectra relative to the rest.
- The five band spectra are statistically consistent with the all-sky reference (departure probabilities 13-71%), and targeted checks around Centaurus, NGC 253, and NGC 1068 show no significant feature attributable to those regions; the northernmost band also matches Telescope Array’s independent measurement of the same sky.
- Hence whatever produces the instep operates identically across the sky - consistent with a propagation/composition effect of a broadly distributed source population (narrow rigidity maximum, He/CNO interplay) and inconsistent with a few-foreground-source origin, up to the statistical power available (fluctuations still prevent conclusions inside the 24-degree Centaurus window itself).
Validity verdict (step 6)
Reconstruction: premise = a handful of localized sources with distinctive spectra would imprint declination-dependent band spectra; observation = five bands statistically consistent with the all-sky spectrum (departure probabilities 13-71%) plus targeted null checks. Conclusion is properly hedged (“disfavors”, “favors”). Traced the load-bearing modus-tollens-shaped evidential step. Undercutting probe: a source configuration arranged to mimic isotropy across bands, or sources below the statistical power - both are covered by the explicit “up to the statistical power available” hedge in the body. Valid as stated.
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