{"paper":{"title":"The hydrodynamics of stratified ultra-relativistic outflows and the origin of GRB X-ray plateaus","license":"http://creativecommons.org/licenses/by/4.0/","headline":"Stratified ultra-relativistic outflows produce GRB X-ray plateaus through forward shock emission.","cross_cats":[],"primary_cat":"astro-ph.HE","authors_text":"Gilad Sadeh, Kenta Hotokezaka, Masaru Shibata","submitted_at":"2026-02-27T15:22:03Z","abstract_excerpt":"The origin of the X-ray plateau phase observed in a large fraction of gamma-ray burst afterglows remains debated. We present a novel analytic framework for the hydrodynamics of ultra-relativistic, radially stratified outflows interacting with an external medium. By explicitly accounting for a continuous distribution of Lorentz factors within the ejecta, we derive analytic expressions describing the evolution of a long-lived, mildly relativistic reverse shock and determine its crossing time. Then, we compute the resulting synchrotron emission from both the forward and reverse shocks. The forwar"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"The forward shock naturally produces a shallow, long-lasting X-ray decay consistent with the observed properties of X-ray plateaus, including the Dainotti relation, without requiring prolonged central-engine activity or an additional high-energy emission component.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"Reproducing the observed plateau durations requires a broad distribution of ejecta Lorentz factors extending down to γ_min ∼70-100, which is assumed to be launched as part of the ultra-relativistic outflow powering the prompt emission.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"Stratified ultra-relativistic outflows with broad Lorentz factor distributions explain GRB X-ray plateaus via forward shock emission while producing long-lived reverse shock millimeter radiation.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"Stratified ultra-relativistic outflows produce GRB X-ray plateaus through forward shock emission.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"62b1a7eb017ddd71ecbdb7cbe9cc11a4859d1509d35215d8530065e86721cfed"},"source":{"id":"2602.24085","kind":"arxiv","version":4},"verdict":{"id":"46e80c3e-f039-4c9a-a770-681cffa31506","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-15T18:48:54.979217Z","strongest_claim":"The forward shock naturally produces a shallow, long-lasting X-ray decay consistent with the observed properties of X-ray plateaus, including the Dainotti relation, without requiring prolonged central-engine activity or an additional high-energy emission component.","one_line_summary":"Stratified ultra-relativistic outflows with broad Lorentz factor distributions explain GRB X-ray plateaus via forward shock emission while producing long-lived reverse shock millimeter radiation.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"Reproducing the observed plateau durations requires a broad distribution of ejecta Lorentz factors extending down to γ_min ∼70-100, which is assumed to be launched as part of the ultra-relativistic outflow powering the prompt emission.","pith_extraction_headline":"Stratified ultra-relativistic outflows produce GRB X-ray plateaus through forward shock emission."},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2602.24085/integrity.json","findings":[],"available":true,"detectors_run":[],"snapshot_sha256":"c28c3603d3b5d939e8dc4c7e95fa8dfce3d595e45f758748cecf8e644a296938"},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}