Open AccessThe relationship between X‐ray variability and the central black hole mass
Author(s) -
Lu Youjun,
Yu Qingjuan
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04344.x
Subject(s) - physics , qsos , astrophysics , black hole (networking) , active galactic nucleus , galaxy , luminosity , astronomy , redshift , stellar mass , supermassive black hole , binary black hole , quasar , intermediate mass black hole , star formation , gravitational wave , routing (electronic design automation) , computer science , link state routing protocol , routing protocol , computer network
We assembled a sample of Seyfert 1 galaxies, quasi‐stellar objects (QSOs) and low‐luminosity active galactic nuclei (LLAGNs) observed by ASCA , the central black hole masses of which have been measured. We found that the X‐ray variability (which is quantified by the ‘excess variance’ σ rms 2 ) is significantly anti‐correlated with the central black hole mass, and it is likely that a linear relationship of σ rms 2 ∝ M bh −1 exists. It can be interpreted that the short time‐scale X‐ray variability is caused by some global coherent variations in the X‐ray emission region, which is scaled by the size of the central black hole. Hence the central black hole mass is the driving parameter of the previously established relation between X‐ray variability and luminosity. Our findings favour the hypothesis that the narrow‐line Seyfert 1 galaxies and QSOs harbour smaller black holes than the broad‐line objects, and can also easily explain the observational fact that high‐redshift QSOs have greater variability than local AGNs at a given luminosity. Further investigations are needed to confirm our findings, and a large sample X‐ray variability investigation can give constraints on the physical mechanisms and evolution of AGNs.