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| Auteur principal: | |
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| Format: | Preprint |
| Publié: |
2026
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| Sujets: | |
| Accès en ligne: | https://arxiv.org/abs/2603.10311 |
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- We propose a variable ADAF disk model for X-ray binary systems. In this model, the accretion flow consists of an outer thin disk and an inner optically thick advection-dominated accretion flow (ADAF) torus. The size of the turbulent ADAF is variable. A complete cycle of ADAF contraction, transition to a thin disk, and subsequent re-expansion corresponds to the rapid rise, peak, and decay phases observed in the X-ray outbursts of black hole binaries. This cycle also tracks the canonical evolution through the low-hard, high-soft, and back to the low-hard state in the hardness-intensity diagram. The model unifies the presence of near-ISCO Fe emission lines with the truncated disk paradigm, as observed in the black hole system GX 339-4. It explains the 35-day period in the neutron star system Her X-1 more effectively through variable ADAF sizes than through a precessing disk. This variable ADAF framework may be extended to explain similar phenomena in active galactic nuclei.