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.

Cores of globular clusters are an ideal place for close encounters between stars. The outcome of tidal capture can be stellar mergers, close binaries between normal stars (W UMa type), cataclysmic variables composed of white dwarf and normal star pairs, or low-mass X-ray binaries consisting of a neutron star and a normal star pairs. Stellar mergers can be the origin of blue stragglers in dense globular clusters although they are hard to observe. Low mass X-ray binaries would eventually become binary pulsars with short pulse periods after the neutron stars accrete sufficient amount of matter from the companion. However, large number of recently discovered, isolated millisecond pulsars (as opposed to binary pulsars) in globular clusters may imply that they do not have to gain angular speeds during the X-ray binary phase. We propose that these isolated millisecond pulsars may have formed through the disruptive encounters, which lead to the formation of accretion disk without Roche lobe filling companion, between a neutron star and a main-sequence star. Based on recently developed multicomponent models for the dynamical evolution of globular clusters, we compute the expected numbers of various systems formed by tidal capture as a function of time.

We present the Hilbert-Huang transform (HHT) analysis on the quasi-periodic modulation of SMC X-1. SMC X-1, consistingof a neutron star and a massive companion, exhibits superorbital modulation with a period varying between ~40 d and ~65 d.We applied the HHT on the light curve observed by the All-Sky Monitor onboard Rossi X-ray Timing Explorer (RXTE) to obtainthe instantaneous frequency of the superorbital modulation of SMC X-1. The resultant Hilbert spectrum is consistent with thedynamic power spectrum while it shows more detailed information in both the time and frequency domains. According to theinstantaneous frequency, we found a correlation between the superorbital period and the modulation amplitude. Combiningthe spectral observation made by the Proportional Counter Array onboard RXTE and the superorbital phase derived in theHHT, we performed a superorbital phase-resolved spectral analysis of SMC X-1. An analysis of the spectral parameters versusthe orbital phase for different superorbital states revealed that the diversity of nH has an orbital dependence. Furthermore,we obtained the variation in the eclipse profiles by folding the All Sky Monitor light curve with orbital period for differentsuperorbital states. A dip feature, similar to the pre-eclipse dip of Her X-1, can be observed only in the superorbital ascendingand descending states, while the width is anti-correlated with the X-ray flux.