Black hole X-ray binaries are bright accreting systems that can undergo apparent state changes on the reasonable timescales for human. These systems are good analogy to their supermassive counterparts: active galactic nuclei. X-ray reflection spectroscopy is a powerful tool to study the accretion geometry under different regimes. In this talk, I will present how we use X-ray reflection spectroscopy to study the inner disk radius during the state transition. I also address the importance to consider high-density models when fitting the reflection spectra of XRBs. In the end, the implementation of this method to test gravity theories will be discussed.
Host: Junjie Mao
