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The propagation length of high-energy photons through the Universe is limitedby $e^+e^-$ pair production on the extragalactic background radiation. Previousstudies reported discrepancies between predicted and observed attenuation,suggesting explanations in terms of new physics. However, these effects aredominated by a limited number of observed sources, while many do not show anydiscrepancy. Here, we consider the distribution in the sky of these apparentlyanomalous objects, selected in two very different approaches: the study ofunphysical hardenings at distance-dependent energies in deabsorbed spectra ofTeV blazars, and the observation of ultra-high-energy air showers from thedirections of BL Lac type objects. In both cases, directions to the anomaloussources follow the projected local distribution of galaxies: all the distantsources, contributing to the anomalies, are seen through the local filament.This matches the prediction of the proposed earlier explanation of theanomalies based on mixing of photons with axion-like particles in thefilament's magnetic field. For ultra-high energies, this axion interpretationmay be tested by the search of primary gamma rays.

The local-filament pattern in the anomalous transparency of the Universe for energetic gamma rays