Recently, The Astrophysical Journal published the latest work about the thermal reprocessing of reflected radiation in the active galactic nuclei (AGNs) accretion disk. This work was conducted by Phd. Student ZHONG Xiaogu and Prof. WANG Jiancheng from Yunnan Observatories of the Chinese Academy of Sciences. Their results imply that the General Relativity plays an important role in the reprocessing of reflected radiation in the AGNs accretion disk.

The radiation emitted from AGNs is powered by matter accreting into supermassive black holes at the center of galaxies and almost covers the broadband spectrum from radio to gamma-ray. The X-ray emission is usually considered to be from the hot corona above the disk via Compton scattering, while the optical/ultraviolet (UV) emission is often considered to be from the cool accretion disk via viscosity or reflection.

However, the details of the geometry of the corona and the kinematics of the accretion disk are not well understood. Recently several researchers have shown that the temperature–radius relationship is not consistent with the standard disk model by studying the wavelength-lag relationship. This is a major challenge to the accretion disk theory with implications that are not yet understood.

In order to analyze the disk-corona construction, the researchers suggested that the General Relativity should be considered because strong gravity is prominent near black holes and photons emitted from the corona to the disk or from the disk to the distant observer would be moving in a curved trajectory (null geodesics), which will add extra time from corona to disk or from disk to the distant observer.

Then, some of these photons absorbed by the accretion disk could heat the accretion disk rapidly and reconstruct the disk temperature profile to change the disk blackbody radiation. Based on the above assumptions, the researchers utilized Yun-Nan Observatory Geodesics Kerr (YNOGK), an algorithm developed by Dr. YANG Xiaolin from Yunnan Observatories of the Chinese Academy of Sciences, to calculate the wavelength-lag relationship.

The work considered with the General Relativity effect interpreted successfully the multi-waveband observation data of NGC4151, Mrk509, NGC5548 and NGC4593, which implied the actual geometry of the disk corona is more complex than the lamppost model prediction.

Contact:

ZHONG Xiaogu, Yunnan Observatories, CAS

E-mail: guqian29@ynao.ac.cn