(I) X-ray relativistic Fe line and black hole spin in Narrow-Line Seyfert 1 galaxies  

   (II) New frontiers in wide-field time-domain high-energy astrophysics　　 

　　Speaker: Weimin Yuan (NAOC)  

　　Time: Thursday, 3:00pm, November 20th　　 

　　Location: Lecture Hall, 3rd floor 　　 

　　Abstract: (I) Relativistic Fe emission line observed in the X-ray spectra of typical Seyfert galaxies is a powerful diagnostic of the spin and surroundings of the central black holes. A long-standing question is whether such a feature is also present in Narrow-Line Seyfert 1 (NLS1) galaxies, which are thought to be at an early phase of black hole growth. By stacking the XMM-Newton X-ray spectra of a large sample, we show that a relativistic Fe line may in fact be common in NLS1s. We find, for the first time, that the black holes are likely spinning at averagely low or moderate rates for NLS1 galaxies as a population. The implications of the results are discussed in the context of the black hole growth scenario. 　　 

　　(II) Transients and variable sources pervade the X-ray universe, some as spectacular outbursts. The study of high-energy transients has greatly advanced our understanding of the dynamic Universe. In recent years new phenomena continue to be discovered and appeal for observations on a large scale for characterization, while others are highly expected and await discovery. I will discuss the key science questions presented by these new developments in wide-field time-domain high-energy astrophysics, as well as the technology needed to open up new frontiers. Last, I will introduce briefly the Einstein Probe, which is a candidate mission in the CAS Pilot Space Science Program, as well as its promise to expand new frontiers in this exciting field.