{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"f0f6b65dbe19e39dbf48c774e81ba40c941e5b6d1c26ebc73f37b0da78af8c1b","created":"2026-10-03T07:17:54Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"6196fee46794b06db468e197877b7411e9b56451bd61fc53329b2ba15f7e49cd","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"astro.cosmic-ray-origins.knee-origin","kind":"phenomenon","literature_status":"partially-resolved","n":"1","parents":[],"plain":"The number of cosmic rays falls off faster above about $3e15\\,\\mathrm{eV}$, a feature called the knee, which may mark the highest energy the Milky Way's particle accelerators reach.","posed_since":"1958","precise":"The all-particle spectrum steepens from dN/dE ~ E^-2.7 to ~E^-3.1 near $E \\sim 3-4\\,\\mathrm{PeV}$, and LHAASO finds that the proton spectrum hardens and then breaks sharply near 3 PeV. Determine which Galactic source class (supernova remnants, young massive star clusters, microquasars, the Galactic center) accelerates protons to at least 3 PeV, and whether the knee is a source maximum-rigidity feature ($E_{\\mathrm{max}}$ proportional to charge $Z$) or a propagation feature. Answer: an identified PeVatron class with an acceleration model reproducing the proton and helium knee positions.","problem_ref":null,"references":"","settled_by":"Composition-resolved spectra of protons, helium and heavier groups up to 100 PeV showing rigidity-ordered breaks, plus spatial identification of PeV proton sources through hadronic gamma rays above 100 TeV or neutrinos.","status_note":"2025: LHAASO measured a proton-only knee at about 3 PeV after a spectral hardening, supporting a rigidity-dependent source cutoff; the source class is unidentified.","title":"What produces the cosmic-ray knee near 3 PeV?","topic_ref":"f43296f47e522e13af620cd00eea18765794669715c801e5fb034a7d89800844"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"1b487bd2a57e219f95646aa3ba694016eb080e96dbda690e183584ccb77fd11c","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"9ad71290b004c04e66eea09e6e11b3b61b8c533ab0bff53262578f8d290038f3","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"RU4EFZquTt6IxBzd8tXeePkWVM7Lll-dp376VnpcA01I07e9s0unnFxm9HzC-VAHb5jrE-X4I6vRRubtTMtUDA"},"schema":"pubphys.envelope/1"},"record_hash":"1b487bd2a57e219f95646aa3ba694016eb080e96dbda690e183584ccb77fd11c","leaf_index":514}