Dr. LU Kaixing from Yunnan Observatories of the Chinese Academy of Sciences, together with collaborator, found that the variability of active galactic nuclei (AGN) with different accretion rates may be caused by the same physical mechanism, and they presented a potential method to estimate the size of the broad-line region.

This study, published online in The Astrophysical Journal, enables people to better understand the accretion physics of AGN, and is helpful for developing the correlation research of accretion disk and broad-line region.

Based on the stochastic behavior of AGN continuum variability, the researchers employed damped random walk model to delineate the light curves of AGN, where the model parameters were estimated using Markov Chain Monte Carlo algorithm.

The team found that the underlying signal of AGN optical variability can be recovered by damped random walk model, and the correlations between optical variability characteristics and AGN properties are smooth from sub-Eddington to super-Eddington accretion AGNs, probably implying that the variability of AGN with different accretion rates may be caused by the same physical mechanism.

Another interesting finding is that the time delay of the broad-emission line with respect to AGN continuum variation correlates with characteristic variability timescale. This 1:1 relation provides a new method to estimate the size of broad-line region.

"However, further research from observation and theory is necessary to explore the probable origin of this 1:1 relation," Dr. LU said.

"The variation of AGN continuum emission is a common feature. Many astronomers with increasing interest attempt to understand the physical origin of AGN’s multi-band variability, but we have a long way to go," Dr. LU added.