ON THE ROLE AND ORIGIN OF NONTHERMAL ELECTRONS IN HOT ACCRETION FLOWS

	ON THE ROLE AND ORIGIN OF NONTHERMAL ELECTRONS IN HOT ACCRETION FLOWS
	Niedzwiecki, Andrzej 1; Stepnik, Agnieszka 1; Xie, Fu-Guo 2
刊名	ASTROPHYSICAL JOURNAL
	2015-02-01
卷号	799 期号:2 页码:1
关键词	accretion black hole physics galaxies: active accretion disks
英文摘要	We study the X-ray spectra of tenuous, two-temperature accretion flows using a model involving an exact, Monte Carlo computation of the global Comptonization effect as well as a general relativistic description of both the flow structure and radiative processes. In our previous work, we found that in flows surrounding supermassive black holes, thermal synchrotron radiation is not capable of providing a sufficient seed photon flux to explain the X-ray spectral indices as well as the cut-off energies measured in several best-studied active galactic nuclei (AGNs). In this work, we complete the model by including seed photons provided by nonthermal synchrotron radiation and we find that it allows us to reconcile the hot flow model with the AGN data. We take into account two possible sources of nonthermal electrons. First, we consider e(+/-) produced by charged-pion decay, which should always be present in the innermost part of a two-temperature flow due to proton-proton interactions. We find that for a weak heating of thermal electrons (small delta) the synchrotron emission of pion-decay e(+/-) is much stronger than the thermal synchrotron emission in the considered range of bolometric luminosities, L similar to (10(-4)-10(-2)) L-Edd. The small-delta model including hadronic effects, in general, agrees with the AGN data, except for the case of a slowly rotating black hole and a thermal distribution of protons. For large delta, the pion-decay e(+/-) have a negligible effect and, in this model, we consider nonthermal electrons produced by direct acceleration. We find an approximate agreement with the AGN data for the fraction of the heating power of electrons, which is used for the nonthermal acceleration eta similar to 0.1. However, for constant eta and delta, the model predicts a positive correlation of the X-ray spectral index with the Eddington ratio, and hence a fine tuning of eta and/or delta with the accretion rate is required to explain the negative correlation observed at low luminosities. We note a significant difference between the dependence of plasma parameters, T-e and tau, on the Eddington ratio that is predicted by the large- and small-delta models. This may be the key property allowing for the estimation of the value of delta. However, a precise measurement of the spectral cut-off is required, and we note that differences between results available in the literature are similar in magnitude to the difference between the model predictions. In flows surrounding stellar-mass black holes, the synchrotron emission of pion-decay e(+/-) exceeds the thermal synchrotron only above similar to 0.01 L-Edd. Furthermore, in such flows, the nonthermal synchrotron radiation is emitted at energies of greater than or similar to 1 keV, and therefore the Compton cooling is less efficient than in flows surrounding supermassive black holes. This may explain spectral differences between AGNs and black-hole transients around similar to 0.01 L-Edd (the latter being typically much harder).
WOS标题词	Science & Technology ; Physical Sciences
类目[WOS]	Astronomy & Astrophysics
研究领域[WOS]	Astronomy & Astrophysics
关键词[WOS]	ACTIVE GALACTIC NUCLEI ; ADVECTION-DOMINATED ACCRETION ; X-RAY BINARIES ; BLACK-HOLE ; RELATIVISTIC PROTONS ; NGC 5548 ; COMPTONIZATION ; SYNCHROTRON ; MODEL ; SIMULATIONS
收录类别	SCI
语种	英语
WOS记录号	WOS:000348820900104
内容类型	期刊论文
源URL	[http://119.78.226.72/handle/331011/18203]
专题	上海天文台_星系宇宙学重点实验室
作者单位	1.Univ Lodz, Dept Astrophys, PL-90236 Lodz, Poland 2.Chinese Acad Sci, Shanghai Astron Observ, Key Lab Res Galaxies & Cosmol, Shanghai 200030, Peoples R China
推荐引用方式 GB/T 7714	Niedzwiecki, Andrzej,Stepnik, Agnieszka,Xie, Fu-Guo. ON THE ROLE AND ORIGIN OF NONTHERMAL ELECTRONS IN HOT ACCRETION FLOWS[J]. ASTROPHYSICAL JOURNAL,2015,799(2):1.
APA	Niedzwiecki, Andrzej,Stepnik, Agnieszka,&Xie, Fu-Guo.(2015).ON THE ROLE AND ORIGIN OF NONTHERMAL ELECTRONS IN HOT ACCRETION FLOWS.ASTROPHYSICAL JOURNAL,799(2),1.
MLA	Niedzwiecki, Andrzej,et al."ON THE ROLE AND ORIGIN OF NONTHERMAL ELECTRONS IN HOT ACCRETION FLOWS".ASTROPHYSICAL JOURNAL 799.2(2015):1.