未改变的脉冲星：GRO J1750-27，一颗不眨眼的超临界X射线中子星
The unaltered pulsar: GRO J1750-27, a super-critical X-ray neutron star that does not blink an eye
摘要：
当吸积X射线星体（XRP）经历明亮的X射线爆发时，可以详细分析它们的光度依赖的光谱和定时特征。XRP GRO J1750-27最近经历了一次此类事件，在此期间使用$NuSTAR$进行观察，并使用$NICER$进行监测。这样的数据集是很难获得的，因为它在一个多月的时间里以总是超过${\sim}5\times10^{37}\,$ erg/s的光度对爆发进行采样。这个值大于典型的临界光度值，在临界光度值下，辐射激波在中子星表面上方形成。我们的联合光谱的数据分析返回一个高度（$N_H\sim(5-8)\times10^{22}\,$ cm $^{-2}$）吸收光谱，显示一个K $α$铁线，一个软黑体组件可能起源于吸积盘的内边缘，并证实了最深的回旋加速器线之一的发现，在${\sim}44\,$ keV的质心能量对应的磁场强度为$4.7\times10^{12}\,$ G。这个值是独立支持的吸积XRP光谱形成的最佳拟合的物理模型，在最近的研究结果，有利于$14$千秒差距的距离，也反映了散装康普顿为主的吸积流。与理论预期和来自其他类似来源的观测证据相反，$NICER$通过爆发上升、峰值和衰减观测到的脉冲轮廓保持显著稳定。的$NICER$频谱，包括铁K $α$线最佳拟合参数，也几乎保持不变，在所有探测的爆发阶段，类似的脉冲分数的行为。我们认为，所有这些现象都是相互联系的，并解释它们是由于吸积柱的发射，这发生在高光度制度的饱和效应。
英文摘要：
When accreting X-ray pulsars (XRPs) undergo bright X-ray outbursts, their luminosity-dependent spectral and timing features can be analysed in detail. The XRP GRO J1750-27 recently underwent one of such episodes, during which it was observed with $NuSTAR$ and monitored with $NICER$. Such a data set is rarely available, as it samples the outburst over more than a month at a luminosity that is always exceeding ${\sim}5\times10^{37}\,$erg/s. This value is larger than the typical critical luminosity value, where a radiative shock is formed above the neutron star's surface. Our data analysis of the joint spectra returns a highly ($N_H\sim(5-8)\times10^{22}\,$cm$^{-2}$) absorbed spectrum showing a K$α$ iron line, a soft blackbody component likely originating from the inner edge of the accretion disk, and confirms the discovery of one of the deepest cyclotron lines, at a centroid energy of ${\sim}44\,$keV corresponding to a magnetic field strength of $4.7\times10^{12}\,$G. This value is independently supported by the best-fit physical model for spectral formation in accreting XRPs which, in agreement with recent findings, favours a distance of $14$ kpc and also reflects a bulk-Comptonization dominated accretion flow. Contrary to theoretical expectations and observational evidence from other similar sources, the pulse profiles as observed by $NICER$ through the outburst raise, peak and decay remain remarkably steady. The $NICER$ spectrum, including the iron K$α$ line best-fit parameters, also remain almost unchanged at all probed outburst stages, similar to the pulsed fraction behaviour. We argue that all these phenomena are linked and interpret them as resulting from a saturation effect of the accretion column's emission, which occurs in the high-luminosity regime.
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