A toy model for the X-ray spectral variability of active galactic nuclei

	A toy model for the X-ray spectral variability of active galactic nuclei
	Cao, Xinwu1,2,3 ; Wang, Jun-Xian 4
刊名	MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
	2014-10-11
卷号	444 期号:1 页码:L20-L24
关键词	accretion black hole physics galaxies: active accretion discs
通讯作者	曹新伍
英文摘要	Investigations into the long-term X-ray spectral variability of 10 active galactic nuclei (AGNs) revealed a positive spectral index-flux correlation for each object. An inner advection-dominated accretion flow (ADAF) may connect to a thin disc/corona at a certain transition radius. Both these structures are responsible for the hard X-ray emission in AGNs. The ADAF is hot and its X-ray spectrum is hard, while the corona above the disc is relatively cold and its X-ray spectrum is therefore soft. The radiation efficiency of the ADAF is usually much lower than that of the thin disc. An increase in the transition radius may lead to a decrease in the spectral index (i.e. a hard spectrum) and the X-ray luminosity even if the accretion rate is fixed, and a decrease of transition radius leads to an increase in spectral index. We propose that such X-ray variability is caused by a change in the transition radius. Our model calculations can reproduce the observed index-flux correlations, if the transition radius fluctuates around an equilibrium position and the radiation efficiency of ADAFs is similar to 5 per cent of that for a thin disc. The average spectral index-Eddington ratio correlation for these ten AGNs sample can also be reproduced by our model calculations, if the equilibrium transition radius increases with decreasing mass accretion rate.
WOS标题词	Science & Technology ; Physical Sciences
类目[WOS]	Astronomy & Astrophysics
研究领域[WOS]	Astronomy & Astrophysics
关键词[WOS]	ADVECTION-DOMINATED ACCRETION ; BLACK-HOLE MASS ; K-ALPHA LINE ; SEYFERT-1 GALAXIES ; DISK-CORONA ; ENERGY-DISTRIBUTIONS ; EDDINGTON RATIO ; NGC 4579 ; EMISSION ; BINARIES
收录类别	SCI
语种	英语
WOS记录号	WOS:000344181600003
公开日期	2015-02-14
内容类型	期刊论文
源URL	[http://119.78.226.72//handle/331011/15718]
专题	上海天文台_星系宇宙学重点实验室
作者单位	1.Chinese Acad Sci, Shanghai Astron Observ, Key Lab Res Galaxies & Cosmol, Shanghai 200030, Peoples R China 2.Xiamen Univ, Dept Astron, Xiamen 361005, Fujian, Peoples R China 3.Xiamen Univ, Inst Theoret Phys & Astrophys, Xiamen 361005, Fujian, Peoples R China 4.Univ Sci & Technol China, Dept Astron, Key Lab Res Galaxies & Cosmol, Hefei 230026, Anhui, Peoples R China
推荐引用方式 GB/T 7714	Cao, Xinwu,Wang, Jun-Xian. A toy model for the X-ray spectral variability of active galactic nuclei[J]. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY,2014,444(1):L20-L24.
APA	Cao, Xinwu,&Wang, Jun-Xian.(2014).A toy model for the X-ray spectral variability of active galactic nuclei.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY,444(1),L20-L24.
MLA	Cao, Xinwu,et al."A toy model for the X-ray spectral variability of active galactic nuclei".MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 444.1(2014):L20-L24.