{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/an-electron-scattering-time-delay-in-black","title":"An Electron-Scattering Time Delay in Black Hole Accretion Disks","arxiv_id":"2209.14304","date":"2022-09-28","proceeding":null,"authors":["Greg Salvesen"],"abstract":"Universal to black hole X-ray binaries, the high-frequency soft lag gets longer during the hard-to-intermediate state transition, evolving from ${\\lesssim}1~{\\rm ms}$ to ${\\sim}10~{\\rm ms}$. The soft lag production mechanism is thermal disk reprocessing of non-thermal coronal irradiation. X-ray reverberation models account for the light-travel time delay external to the disk, but assume instantaneous reprocessing of the irradiation inside the electron scattering-dominated disk atmosphere. We model this neglected scattering time delay as a random walk within an $\\alpha$-disk atmosphere, with approximate opacities. To explain soft lag trends, we consider a limiting case of the scattering time delay that we dub the thermalization time delay, $t_{\\rm th}$; this is the time for irradiation to scatter its way down to the effective photosphere, where it gets thermalized, and then scatter its way back out. We demonstrate that $t_{\\rm th}$ plausibly evolves from being inconsequential for low mass accretion rates $\\dot{m}$ characteristic of the hard state, to rivaling or exceeding the light-travel time delay for $\\dot{m}$ characteristic of the intermediate state. However, our crude model confines $t_{\\rm th}$ to a narrow annulus near peak accretion power dissipation, so cannot yet explain in detail the anomalously long-duration soft lags associated with larger disk radii. We call for time-dependent models with accurate opacities to assess the potential relevance of a scattering delay.","url_abs":"https://arxiv.org/abs/2209.14304v2","url_pdf":"https://arxiv.org/pdf/2209.14304v2.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"an-electron-scattering-time-delay-in-black","repo_url":"https://github.com/gregsalvesen/thermdelay","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}