Black hole X-ray binaries (BHXBs) are key laboratories for studying accretion physics, relativistic jets, and strong gravity. Since its launch in 2017, NASA’s Neutron Star Interior Composition Explorer (NICER) has provided unprecedented X-ray timing and spectral data, enabling new insights into accretion phenomenology and the physics behind. In this talk, I will review what we have learned...
Low-frequency quasi-periodic oscillations (LFQPOs) are among the most striking timing features in black hole X-ray binaries, yet their physical origin and diversity remain unresolved. In this talk, I will present a new framework that naturally explains the transition from type C to type B QPOs through the progressive warping of the accretion disk. I will show that when the transition radius of...
Based on the AGNSED model (Kubota & Done 2018), we developed a spectral model, SSsed, which describes the disc–corona geometry in stellar-mass black hole binaries. We applied this model to RXTE spectral datasets of XTE J1550–564 and compared the estimated coronal radii
$R_{\rm cor}$ with independently determined centroid frequencies of low-frequency QPOs in their power density spectra. In...
In recent years, fast optical-infrared (O-IR) variability of LMXBs has opened a new window in the study of the jet and accretion flow properties. All objects observed thus far are known to have an intermediate-high inclination, biasing our interpretations and hampering the possibility of adequately testing models. Here, I present the first sub-second multiwavelength analysis of low inclination...
It is widely accepted that Type-B quasi-periodic oscillations (QPOs) are causally connected to discrete ejections of relativistic jets in black hole X-ray binaries. Here, I present new results from a bright flare of Swift J1727.8−1613, during which the source evolved from the hard intermediate state (HIMS) into the soft intermediate state (SIMS) and almost immediately back to the HIMS, without...
Fast multi-wavelength studies of black hole transients are revealing a complex and rich phenomenology, opening a new era in the study of disc-jet coupling. In this talk, I will show the latest results regarding an X-ray/Optical and infrared (O-IR) campaign on the bright transient Swift J1727.8-1613. By following the source with NICER, Ultracam HAWKI, and HIPERCAM, for the first time, we were...
