Title: Disc reflection in low-mass X-ray binaries 

　　Speaker: Dr. Yanan Wang (王亚楠; University of Groningen) 

　　Location：Middle Conference Room, 3rd floor 

　　Time: 2:00 pm, April 18 (Thursday) 

　　Abstract: X-ray binary systems, with either a black hole or a neutron star, provide a unique window into the physics of strong gravity and ultra-dense matter in a realm that cannot be attained in man-made laboratories. In such binaries, matter from the companion star gets accreted onto the compact object forming an accretion disc and the gravitational energy released in the process is believed to be the main source of their power. However, the observed X-ray energy has been found to be much harder than that expected from the disc emission. This Comptonised emission has been proposed to arise from ‘corona’.
Detailed spectral and timing analysis of disc reflection – a product of the interaction between the disc and the corona – can yield insights into the accretion morphology, in particular, the inner radial extent of the accretion disc as well as of the extent and location of the primary Comptonised source. During the course of my PhD, our detailed studies of X-ray binaries yielded several interesting results. For instance, we found that direct and the reflected emission were related differently on different timescales in the black-hole candidate IGR J17091-3624; we were able to offer a solution to the debated high-inclination issue in the neutron star 4U 1636-53 with the model assuming a lamppost geometry of the corona; in the neutron star 4U 1728-34, the disc iron abundance required by the data is as high as 10 times solar. In this talk, I will present these findings from our study of the three X-ray binaries and discuss the pros and cons of the current disc reflection models.