A MODEL FOR THE CORRELATION OF HARD X-RAY INDEX WITH EDDINGTON RATIO IN BLACK HOLE X-RAY BINARIES

	A MODEL FOR THE CORRELATION OF HARD X-RAY INDEX WITH EDDINGTON RATIO IN BLACK HOLE X-RAY BINARIES
	Qiao, Erlin; Liu, B. F.
刊名	ASTROPHYSICAL JOURNAL
	2013-02-10
卷号	764 期号:1
关键词	accretion, accretion disks black hole physics X-rays: individual (H1743-322) X-rays: stars
英文摘要	Observations show that there is a positive correlation between the Eddington ratio lambda and hard X-ray index Gamma for lambda greater than or similar to 0.01, and there is an anti-correlation between lambda and Gamma for lambda less than or similar to 0.01 in black hole X-ray binaries (with lambda = L-bol/L-Edd). In this work, we theoretically investigate the correlation between Gamma and lambda within the framework of a disk-corona model. We improve the model by taking into account all cooling processes, including synchrotron and self-Compton radiations in the corona, Comptonization of the soft photons from the underlying accretion disk, and the bremsstrahlung radiations. Presuming that the coronal flow above the disk can reach up to the 0.1 Eddington rate at the outer region, we calculate the structure of the two-phase accretion flows and the emergent spectra for accretion rates from 0.003 to 0.1. We find that at accretion rates larger than similar to 0.01 Eddington rate, a fraction of coronal gas condenses into the disk and an inner disk can be sustained by condensation. In this case, the X-ray emission is dominated by the scattering of the soft photon from the underlying disk in the corona. The emission from the inner disk and corona can produce the positive correlation between lambda and Gamma. While at accretion rates lower than similar to 0.01 Eddington accretion rate, the inner disk vanishes completely by evaporation, and the accretion is dominated by advection-dominated accretion flows (ADAFs), in which the X-ray emission is produced by the Comptonization of the synchrotron and bremsstrahlung photons of ADAF itself. The emission from ADAFs can produce the anti-correlation between lambda and Gamma. We show that our model can roughly explain the observed evolution of Gamma(3-25 keV) with L0.5-25 keV/L-Edd for the black hole X-ray transient H1743-322 in the decay of 2003 from the thermal-dominated state to low/hard state.
收录类别	SCI
语种	英语
WOS记录号	WOS:000314335200002
内容类型	期刊论文
源URL	[http://ir.bao.ac.cn/handle/114a11/5965]
专题	国家天文台_空间科学研究部
作者单位	Chinese Acad Sci, Natl Astron Observ, Beijing 100012, Peoples R China
推荐引用方式 GB/T 7714	Qiao, Erlin,Liu, B. F.. A MODEL FOR THE CORRELATION OF HARD X-RAY INDEX WITH EDDINGTON RATIO IN BLACK HOLE X-RAY BINARIES[J]. ASTROPHYSICAL JOURNAL,2013,764(1).
APA	Qiao, Erlin,&Liu, B. F..(2013).A MODEL FOR THE CORRELATION OF HARD X-RAY INDEX WITH EDDINGTON RATIO IN BLACK HOLE X-RAY BINARIES.ASTROPHYSICAL JOURNAL,764(1).
MLA	Qiao, Erlin,et al."A MODEL FOR THE CORRELATION OF HARD X-RAY INDEX WITH EDDINGTON RATIO IN BLACK HOLE X-RAY BINARIES".ASTROPHYSICAL JOURNAL 764.1(2013).