Observations of black hole and neutron star X-ray binaries in the past few decades have helped shape current knowledge of accretion onto compact objects, which is also important to the understanding of black hole growth and galaxy evolution on the cosmological time scales. Manifestations of popular black hole accretion models, such as standard geometrically thin disk model, advection-dominated accretion flow (ADAF) model and slim disk model, have all been found in X-ray binaries, forming the current framework of accretion regimes in relative to mass accretion rate onto black holes. In this talk, I will first introduce X-ray spectral state transitions observed in black hole and neutron star X-ray binaries, and then show evidence that an additional parameter, other than the mass accretion rate, is needed to describe the observations. The observations of the outbursts of black hole and neutron star LMXB transients imply a 2-D framework of non-stationary accretion regimes in which the rate-of-change of the mass accretion rate is not negligible. In the end, I will show X-ray spectral state transitions observed in black hole and neutron star X-ray binaries corresponding to extremely low and high mass accretion rate, as well as several cases associated with extreme rate-of-change of the mass accretion rate. I will conclude by pointing out that we need to understand non-stationary accretion regimes and the effects of disk mass in black hole accretion theory.

BIO
Dr. Wenfei Yu earned his Ph.D in particle physics in the Institute of High Energy Physics (IHEP) in Beijing. Later on he worked as a postdoctoral scientist in the Astronomical Institute "Anton Pannekoek” of the University of Amsterdam and the Department of Physics of the University of Illinois at Urbana-Champaign. Then he took a professorship through the Hundred Talents Program of the Chinese Academy of Sciences at Shanghai Astronomical Observatory in late 2006. Since then, he has built an active group on observations of X-ray binaries and accretion-powered X-ray transients, making use of space observations primarily with Swift, XMM-Newton and RXTE and coordinated ground observations in the optical or the radio wavelengths. His current research interests are on the physics of accretion onto compact objects and relativistic astrophysics of compact stars through X-ray timing and spectroscopy. He has been involved in the science team of the Chinese X-ray satellite HXMT, and have served in the science working groups of several future space missions or ground facilities, e.g., SKA, eXTP and SVOM. He is also holding a FAST Fellowship administrated by the Center for Astronomical Mega-Science (CAS).