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SHAO Astrophysics Colloquium

Title Changing-look AGNs: Discoveries and Challenges

Speaker: Xue-Bing Wu (Peking University)

Location: Lecture hall, 3rd floor

Time: 3:00pm on Thursday (Sept.19)

Abstract:The discovery of changing-look (CL) AGNs, with the appearance or disappearance of broad emission lines in the UV/optical spectra within a few years, challenges our understanding of the AGN unification model. We present a sample of 21 new CL AGNs at redshifts between 0.08 and 0.60, which significantly increases the number of such objects known to date. These new CL AGNs were discovered by several ways, from (1) repeat spectra in the SDSS, (2) repeat spectra in the LAMOST and SDSS, and (3) photometric variability and new spectroscopic observations. We confirm a bluer-when-brighter trend in the optical band. However, the mid-infrared WISE colors become redder when the objects become brighter, possibly due to a stronger hot dust re-radiation when the central AGN activity becomes stronger. The physical mechanism of type transition in CL AGNs is still unknown, but preferred to be related to the accretion rate change in the inner part of accretion disks around supermassive black holes. The analogy of state transitions in CL AGNs and black hole X-ray binaries will be discussed.

 
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The Astrophysics division is the main group engaged in astrophysical research at Shanghai Astronomical Observatory. Research areas include active galactic nuclei and high energy astrophysics, galaxy formation and evolution, cosmology and large scale structure, star clusters and the structure of the Milk Way, star formation, and planetary astrophysics. There are now 45 faculty members, 16 postdocs, and 65 graduate students in the division.

The Astrophysics division maintains close partnerships with many astronomical research institutes, including the joint Key laboratory of research in galaxies and cosmology of CAS with University of Science and Technology of China, the joint astrophysics center with Xiamen University. Members of the astrophysics division also participate in many international and domestic astronomical projects, including LAMOST, HXMT, FAST, the Sloan Digital Sky Survey IV, TMT, LSST, etc.

 

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