{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"ec24027b8ac583cf3e62546490315158ce0c2f2fc7686c73d0be29e78a2ede02","created":"2026-10-03T07:17:55Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"3cc14bc5612f3e3cb3ba1134cfc9554e541d12b0c8d39100f8048d70b3a31670","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"classification","assisted_by":[],"external_id":"astro.grb-engines-jets.ep-fast-xray-transients","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Since 2024 the Einstein Probe satellite has found many short X-ray flashes from distant galaxies, some with no gamma rays; they may be gamma-ray bursts seen from the side, weaker jets, or something new.","posed_since":"2024","precise":"Einstein Probe (launched 2024) detects extragalactic fast X-ray transients lasting $\\sim 1\\mathrm{e}2\\ \\text{to}\\ 1\\mathrm{e}4\\,\\mathrm{s}$, several with redshifts, some followed by broad-lined type Ic supernovae, and many without gamma-ray detection. Determine the fractions due to off-axis classical jets, intrinsically slow (low-Lorentz-factor or choked) jets, and shock breakout, and the rate relative to long GRBs. Answer: class fractions and rates from a sample with redshifts and counterparts.","problem_ref":null,"references":"","settled_by":"A complete Einstein Probe sample with redshifts, afterglow modeling and supernova searches, compared with predicted off-axis and low-Lorentz-factor populations.","status_note":"2024-2025: some Einstein Probe transients, for example EP240414a, were followed by broad-lined type Ic supernovae, linking them to collapsing stripped stars.","title":"What are the fast X-ray transients found by Einstein 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