An Ultrahigh-Energy Γ-Ray Bubble Powered by a Super PeVatron

We report the detection of a y-ray bubble spanning at least 100 deg2 in ultra-high energy (UHE) up to a few PeV in the direction of the star-forming region Cygnus X, implying the presence super PeVatron(s) accelerating protons to at least 10 PeV. A log-parabola form with the photon index C(E) = (2.71 +/- 0.02) + (0.11 +/- 0.02) x log10(E/10 TeV) is found fitting the gamma-ray energy spectrum of the bubble well. UHE sources, "hot spots" correlated with very massive molecular clouds, and a quasi-spherical amorphous y-ray emitter with a sharp central brightening are observed in the bubble. In the core of - 0.5 degrees, spatially associating with a region containing massive OB association (Cygnus OB2) and a microquasar (Cygnus X-3), as well as previously reported multi-TeV sources, an enhanced concentration of UHE y-rays is observed with 2 photons at energies above 1 PeV. The general feature of the bubble, the morphology, and the energy spectrum, are reasonably reproduced by the assumption of a particle accelerator in the core, continuously injecting protons into the ambient medium. (c) 2023 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.