论文标题
NGC 4395 ULX1的硬X射线耀斑和光谱变化
Hard X-ray flares and spectral variability in NGC 4395 ULX1
论文作者
论文摘要
我们使用最近的XMM-Newton观测值，首次报告了附近超X射线源（ULX）NGC 4395 ULX1中燃烧事件的检测。耀斑的发作比稳定的发射间隔要硬，从而导致高能量状态的分数变异性更高。一个薄的开普勒式和纤细的积聚磁盘为XMM-Newton Spectra提供了最佳的连续体。所有观察结果均显示出较宽的驼峰状功能左右$ \ sim 0.9 $ keV，可以与混合发射线的集合相关联，并通过与其他显示出类似功能的ULX进行比较，暗示了该ULX中的风/流出。耀斑的光谱对应于较高的细盘温度，这是由于较高的质量吸积率在以对流为主的积聚场景下。不同通量状态中的亮度温度（L-T）值显示出积极的趋势。当以PowerLaw关系为特征时，L-T配置文件与分析数据的$ l \ propto t^2 $和$ l \ propto T^4 $关系均广泛一致。在超级埃德丁顿（Super-Eddington）上积聚到恒星质量的紧凑型物体的情况下，纤薄积聚磁盘的经验预测是$ l \ propto t^2 $，这是ULX1中可能的情况。耀斑事件的起源被理解为吸积率的固有变化或吸积盘内部区域可变的块状风的存在。
We report the detection of flaring events in NGC 4395 ULX1, a nearby ultraluminous X-ray source (ULX), for the first time, using recent XMM-NEWTON observations. The flaring episodes are spectrally harder than the steady emission intervals, resulting in higher fractional variability in the high energy regime. A thin Keplerian and a slim accretion disk provide the best-fit continuum for XMM-NEWTON spectra. All observations show a broad hump-like feature around $\sim 0.9$ keV, which can be associated with a collection of blended emission lines, and suggests the presence of a wind/outflow in this ULX through comparison with other ULXs that show a similar feature. The flaring spectra correspond to higher slim disk temperatures due to higher mass accretion rate under an advection-dominated accretion scenario. The luminosity-temperature (L-T) values in different flux states show a positive trend. When characterized with a powerlaw relation, the L-T profile is broadly consistent with both $L\propto T^2$ and $L\propto T^4$ relations for the analysed data. The empirical predictions for a slim accretion disk in the case of super-Eddington accretion onto a stellar-mass compact object is $L \propto T^2$ which is a possible scenario in ULX1. The origin of the flaring events is understood as an intrinsic change of accretion rate or presence of variable clumpy wind in the inner region of the accretion disk.
