X-ray spectral and timing properties of the black hole binary XTE J1859+226 and their relation to jets.

This article focuses on the comprehensive X-ray and soft gamma-ray spectral and timing analysis of the Galactic black hole binary XTE J1859+226 during its 1999–2000 outburst, using data from RXTE, ASCA, BeppoSAX, and CGRO. The study finds that the innermost radius (r_in) and temperature (T_in) of the accretion disk vary significantly during the rising phase, with r_in stabilizing near ~60 km—interpreted as the innermost stable circular orbit (ISCO)—during the decay phase. Low-frequency quasi-periodic oscillations (QPOs) of Types A, B, and C show distinct correlations with r_in: Type-C QPOs occur when r_in is truncated away from the ISCO and their frequency scales approximately as r_in^(-1), while Types A and B appear near the ISCO with nearly constant r_in. The timing of radio jet ejections coincides with rapid inward movement of r_in toward the ISCO and increases in disk flux, suggesting that jet material originates from the inner accretion disk rather than the hot corona or advection-dominated accretion flow (ADAF). Additionally, spectral modeling constrains the black hole mass to about 7.8 solar masses and indicates a relatively low spin parameter, with distance estimates around 7–8 kpc. The study highlights the importance of simultaneous spectral, timing, and radio observations to understand accretion dynamics and jet formation in black hole X-ray binaries.