标题： 利用V4641 Sgr在低软能谱态时的${\it SWIFT}$和${\it NuSTAR}$观测数据限制其距离和倾角 显示英文标题

标题： Constraining distance and inclination angle of V4641 Sgr using ${\it SWIFT}$ and ${\it NuSTAR}$ observations during low soft spectral state

摘要： 我们展示了V4641人马座在盘主导（软态）以及幂律主导（硬态）状态下，由${\it NuSTAR}$和${\it SWIFT}$/XRT联合光谱分析得到的结果。 软态的光谱可以用相对论模糊盘发射、幂律、宽铁线、两个窄发射线以及两个边缘很好地拟合。 马尔可夫链蒙特卡洛模拟技术和盘及宽铁线中观测到的相对论效应使我们能够自洽地限制内盘半径、盘倾角以及源的距离分别为2.43$^{+0.39}_{-0.17}$R$_g$(GM/c$^2$)，69.5$^{+12.8}_{-4.2}$度和10.8$^{+1.6}_{-2.5}$千秒差距。 对于硬态，光谱表现为具有弱展宽铁线和边缘的幂律。 吸积率的估计给出了爱丁顿比 $L_{2.0 - 80.0 keV}/L_{Edd}$ 的量度，分别为 $\sim$ 1.3 $\times$ 10$^{-2}$ 和 $\sim$ 1.9 $\times$ 10$^{-3}$，分别对应软态和硬态。与大多数其他典型的黑洞系统不同，后者在如此低的吸积率下总是处于硬态，V4641 Sgr 显示出一种以盘为主的软态。 软态光谱在$\sim 6.95$和$\sim 8.31$keV处显示出窄发射线，可以确定它们分别来自X射线辐照风中高度电离的铁和镍的发射。 如果不是由于仪器效应或校准误差，这将是首次在黑洞X射线双星中探测到Ni荧光线。 显示英文摘要

摘要： We present results from ${\it NuSTAR}$ and ${\it SWIFT}$/XRT joint spectral analysis of V4641 Sgr during a disk dominated or soft state as well as a powerlaw dominated or hard state. The soft state spectrum is well modeled by a relativistically blurred disk emission, a powerlaw, a broad Iron line, two narrow emission lines and two edges. The Markov Chain Monte Carlo simulation technique and the relativistic effects seen in the disk and broad Iron line allow us to self-consistently constrain the inner disk radius, disk inclination angle and distance to the source at 2.43$^{+0.39}_{-0.17}$ R$_g$ (GM/c$^2$), 69.5$^{+12.8}_{-4.2}$ degrees and 10.8$^{+1.6}_{-2.5}$ kpc respectively. For the hard state, the spectrum is a power-law with a weakly broad Iron line and an edge. The distance estimate gives a measure of the Eddington fraction, $L_{2.0 - 80.0 keV}/L_{Edd}$, to be $\sim$1.3 $\times$ 10$^{-2}$ and $\sim$1.9 $\times$ 10$^{-3}$ for the soft and hard states respectively. Unlike many other typical black hole systems which are always in a hard state at such low Eddington fraction, V4641 Sgr shows a soft, disk dominated state. The soft state spectrum shows narrow emission lines at $\sim 6.95$ and $\sim 8.31$ keV which can be identified as being due to emission from highly ionized Iron and Nickel in an X$-$ray irradiated wind respectively. If not due to instrumental effect or calibration error, this would be the first detection of a Ni fluorescent line in a black hole X$-$ray binary.