{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"8d7aef036771494f2a3fd5787bf457b006edd355ac0d7a800186531876d92d76","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["1b487bd2a57e219f95646aa3ba694016eb080e96dbda690e183584ccb77fd11c","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"b11192fd7c31ecd65aa5eac76a26b56aa097d9f53581923fc6c12d5d55709c2f","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":"2","parents":[],"plain":"The number of cosmic rays falls off faster above about $3 \\times 10^{15}\\,\\mathrm{eV}$, 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 ($E_{\\max}$ 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":"1b487bd2a57e219f95646aa3ba694016eb080e96dbda690e183584ccb77fd11c","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":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"6c8904a85810fb21eba750a9891b4e56c6a7e46a3b2b51b460162e818c6bf524","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"0b0c5571c43bd82d5838205edfb97cfca03727deb4593fe61de99fa27aa310cd","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"6K6spCHtMMrxp54V0RTMJEoXwVCdhBLZLxaDvIeRW4gPx8WigdJfnnBxt285tnAQ6192FfZQwrj0VDauUlpmDQ"},"schema":"pubphys.envelope/1"},"record_hash":"6c8904a85810fb21eba750a9891b4e56c6a7e46a3b2b51b460162e818c6bf524","leaf_index":2334}