In this work, we study the correlation between the photon index (Γ) of the X-ray spectrum and the 2-10 keV X-ray luminosity (LX) for black hole X-ray binaries (BHBs). The BHB sample is mainly from the quiescent, hard and intermediate states, with values of LX ranging from ~ 1030.5 to 1037.5 erg s-1. We nd that the photon index Γ is positively or negatively correlated with the X-ray luminosity LX, for LX above or below a critical value, ~ 1036.5 erg s-1. This result is consistent with previous works. Moreover, when LX ≤ ~ 1033 erg s-1, we found that the photon index is roughly independent of the X-ray luminosity. We interpret the above correlations in the framework of a coupled hot accretion flow - jet model. Besides, we also find that in the moderate-luminosity region, different sources may have different anti-correlation slopes, and we argue this diversity is caused by the different value of δ, which describes the fraction of turbulent dissipation that directly heats electrons.

Observations show that the accretion ows in low-luminosity active galactic nuclei (LLAGNs) probably have a two-component structure with an inner hot, optically thin, advection dominated accretion flow (ADAF) and an outer truncated cool, optically thick accretion disk. As shown by Taam et al. (2012), within the framework of the disk evaporation model, the truncation radius as a function of mass accretion rate is strongly affected by including the magnetic field. We define the parameter β as pm = B2=8π = (1 - β)ptot, (where ptot = pgas + pm, pgas is gas pressure and pm is magnetic pressure) to describe the strength of the magnetic field in accretion ows. It is found that an increase of the magnetic field (decreasing the value of β) results in a smaller truncation radius for the accretion disk. We calculate the emergent spectrum of an inner ADAF + an outer truncated accretion disk around a supermassive black hole by considering the effects of the magnetic field on the truncation radius of the accretion disk. By comparing with observations, we found that a weaker magnetic field (corresponding to a bigger value of β) is required to match the observed correlation between L2-10keV/LEdd and the bolometric correction K2-10keV, which is consistent with the physics of the accretion ow with a low mass accretion rate around a black hole.

The symbiotic star V1016 Cygni, a detached binary system consisting of a hot white dwarf and a mass-losing Mira variable, shows very broad emission features at around 6825 °A and 7082 °A, which are Raman scattered Ovi  1032, 1038 by atomic hydrogen. In the high resolution spectrum of V1016 Cyg obtained with the Bohyunsan Optical Echelle Spectrograph these broad features exhibit double peak profiles with the red peak stronger than the blue counterpart. However, their profiles differ in such a way that the blue peak of the 7082 feature is relatively weaker than the 6825 counterpart when the two Raman features are normalized to exhibit an equal red peak strength in the Doppler factor space. Assuming that an accretion flow around the white dwarf is responsible for the double peak profiles, we attribute this disparity in the profiles to the local variation of the flux ratio of Ovi  1032, 1038 in the accretion flow. A Monte Carlo technique is adopted to provide emissivity maps showing the local emissivity of Ovi 1032 and Ovi 1038 in the vicinity of the white dwarf. We also present a map indicating the differing flux ratios of Ovi  1032 and 1038. Our result shows that the flux ratio reaches its maximum of 2 in the emission region responsible for the central trough of the Raman feature and that the flux ratio in the inner red emission region is almost 1. The blue emission region and the outer red emission region exhibit an intermediate ratio around 1.5. We conclude that the disparity in the profiles of the two Raman Ovi features strongly implies accretion flow around the white dwarf, which is azimuthally asymmetric.

We present Spitzer IRS spectroscopy of CO2 ice toward 19 young stellar objects (YSOs) with luminosity lower than 1L⊙ . Pure CO2 ice forms only at elevated temperatures, T > 20 K, and thus at higher luminosities. Current internal luminosities of YSOs with L < 1L⊙ do not provide such conditions out to radii of typical envelopes. Significant amounts of pure CO2 ice would signify a higher past luminosity. We analyze 15.2 μm CO2 ice bending mode absorption lines in comparison to the laboratory data. We decompose pure CO2 ice from 12 out of 19 young low luminosity sources. The presence of the pure CO2 ice component indicates high dust temperature and hence high luminosity in the past. The sum of all the ice components (total CO2 ice amount) can be explained by a long period of low luminosity stage between episodic accretion bursts as predicted in an episodic accretion scenario. Chemical modeling shows that the episodic accretion scenario explains the observed total CO2 ice amount best.

열적으로 불안정한 강착원반의 비선형 유체역학적 모형에 기초하여 블랙홀 마이크로케이사의 광폭발 한계 순환주기에 대한 원반 질량의 시간적 진화 모형을 계산하였다. 블랙홀의 질량, 원반 크기 및 질량 유입률과 같은 물리적인 매개변수들은 블랙홀 X선 신성의 원형인 A0620-00에서 관측된 역사적인 1975 광폭발을 재현하도록 선택되었다. 중심부에서 원반으로 쪼여지는 조사(照射)의 시간에 따른 효과는 직접 조사와 원반위의 뜨거운 강착 흐름으로부터 굴절되어 원반에 쪼여지는 간접조사의 두 가지 방법이 고려되었다. 우리의 강착원반 열적 불안정성 모형은 광폭발의 순환과정 전반에 걸쳐 X-선 변광체들에서 관측된 광도의 전형적인 복사 광도를 설명할 수 있다. 강착원반의 최대질량 ∼4.03×1024g은 광폭발의 점화 때에 얻어지며, 최소질량 ∼8.54×1023g은 차가운 쇠퇴기와 정지기(靜止期) 때에 이루어진다. 원반의 질량은 광폭발 한계 순환주기에 걸쳐 약 5배 정도 변한다.

Our examination of the relations of spherically symmetric accretion on a massive point object to viscous drag, neglecting gas pressure and using self-similar transformation, shows the behaviors of the asymptotic solutions? in the regions near to and far from the center. The viscosity reduces the free-fall velocity by the factor (1+ζ)−1, and causes flattening in the density distribution. Therefore, the viscosity leads to the reduction of the mass accretion rate.

An elliptical accretion disk may be formed by tidally disrupted debris of a flying-by star in an active galactic nucleus (AGN) or by tidal perturbation due to a companion in a binary black hole system. We investigate the iron Kα line profiles expecting from a geometrically thin, relativistic, elliptical disk in terms of model parameters, and find that a broad and skewed line profile can be reproduced well. Its shape is variable to the model parameters, such as, the emissivity power-law index, the ellipticity of the disk, and the major axis orientation of the elliptical accretion disk. We suggest that our results may be useful to search for such an elliptical disk and consequently the tidal disruption event.

Radiation hydrodynamics in high. velocity or high optical-depth flow should be treated under rigorous relativistic formalism. Relativistic radiation hydrodynamic moment equations are summarized, and its application to the near-critical accretion onto neutron star is discussed. The relativistic effects can dominate the dynamics of the flow even when the gravity is weak and the velocity is small. First order equations fail to describe the intricate relativistic effects correctly.