{"paper":{"title":"The NuSTAR view of Ultra-Compact X-ray Binaries","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"Ultra-compact X-ray binaries exhibit spectral properties similar to longer-period low-mass X-ray binaries, indicating comparable conditions in their innermost accretion regions.","cross_cats":[],"primary_cat":"astro-ph.HE","authors_text":"A. Borghese, M. Armas Padilla, T. Mu\\~noz-Darias","submitted_at":"2026-04-14T18:10:26Z","abstract_excerpt":"Ultra-compact X-ray binaries (UCXBs) are a subclass of low-mass X-ray binaries (LMXBs) characterised by tight orbits and hydrogen-poor donor stars. We present a spectral and timing study in the hard X-ray band of 11 of the 20 confirmed UCXBs, based on 37 archival NuSTAR observations. Using both X-ray colours and fractional root mean square values, we show that our sample spans the hard, soft, and intermediate X-ray states. Subsequently, we perform an X-ray spectral analysis using, when data allow it, the three-component model - an approach increasingly adopted for neutron star LMXBs. This work"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"UCXBs exhibit similar spectral properties to their longer-period counterparts, suggesting no major differences in the innermost regions of X-ray binaries, regardless of disc size or chemical composition. A possible exception is found in the soft-state sample, which shows Comptonisation fractions higher than those typically observed in regular LMXBs.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"That the three-component model is the appropriate description for UCXB spectra and that the 11-source archival sample adequately represents the full range of UCXB behavior and states.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"Ultra-compact X-ray binaries exhibit similar hard X-ray spectral properties to standard low-mass X-ray binaries, including typical continuum values per state, with higher Comptonisation fractions in soft states and a very cold hard state discovered in 4U 1626-67.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"Ultra-compact X-ray binaries exhibit spectral properties similar to longer-period low-mass X-ray binaries, indicating comparable conditions in their innermost accretion regions.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"d6accd7e740f23c3dbe2f50cf6101af45c51c97a502550a34205b8ce346eb280"},"source":{"id":"2604.13187","kind":"arxiv","version":1},"verdict":{"id":"1c41f257-a399-43b8-a287-1e2b4595745d","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-10T14:01:25.620221Z","strongest_claim":"UCXBs exhibit similar spectral properties to their longer-period counterparts, suggesting no major differences in the innermost regions of X-ray binaries, regardless of disc size or chemical composition. A possible exception is found in the soft-state sample, which shows Comptonisation fractions higher than those typically observed in regular LMXBs.","one_line_summary":"Ultra-compact X-ray binaries exhibit similar hard X-ray spectral properties to standard low-mass X-ray binaries, including typical continuum values per state, with higher Comptonisation fractions in soft states and a very cold hard state discovered in 4U 1626-67.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"That the three-component model is the appropriate description for UCXB spectra and that the 11-source archival sample adequately represents the full range of UCXB behavior and states.","pith_extraction_headline":"Ultra-compact X-ray binaries exhibit spectral properties similar to longer-period low-mass X-ray binaries, indicating comparable conditions in their innermost accretion regions."},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2604.13187/integrity.json","findings":[],"available":true,"detectors_run":[],"snapshot_sha256":"c28c3603d3b5d939e8dc4c7e95fa8dfce3d595e45f758748cecf8e644a296938"},"references":{"count":2,"sample":[{"doi":"","year":1997,"title":"F., Margon, B., Deutsch, E","work_id":"85c548c3-6e73-4319-a684-c7aa1986e169","ref_index":1,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":1916,"title":"B.3:Left:Spectrum of IGR J16597−3704.Right:Spectrum of 4U 1916−053","work_id":"e865c4d2-9db1-4568-a168-8b4d050c733d","ref_index":2,"cited_arxiv_id":"","is_internal_anchor":false}],"resolved_work":2,"snapshot_sha256":"d1a272de7e7a68ba6ca11cc76719112db98d0413d9758a1b2ebc6cee2317123b","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"}