标题： X射线耀斑中κ1猎户座星的冷等离子体延迟发展 显示英文标题

标题： Delayed Development of Cool Plasmas in X-ray Flares from kappa1 Ceti

摘要： 中子星内部组成探测器（NICER）X射线观测台在2019年观测到了附近年轻的类太阳恒星kappa1 Ceti发出的两个相当于超级耀斑的强大X射线爆发。 NICER从耀斑开始到早期衰减阶段都进行了跟踪，峰值附近收集到超过30个计数每秒，使得能够详细研究耀斑上升阶段的光谱变化。 9月份的耀斑在约800秒内迅速变化，而12月份的耀斑具有几倍更长的时间尺度。 在两个耀斑中，硬X射线波段（2-4 keV）的光变曲线表现出典型的恒星X射线耀斑变化，即快速上升和缓慢衰减，而软X射线光变曲线，尤其是9月份的耀斑，具有延长的平坦峰值。 时间分辨光谱需要两个温度等离子体成分，分别为kT ~0.3-1 keV和~2-4 keV。 这两个成分变化相似，但冷成分比热成分滞后约200秒，其发射度（EM）仅为热成分的4-6倍。 与流体力学耀斑环模拟的比较表明，冷成分来源于磁环足点附近的X射线等离子体，主要通过热传导冷却。 时间滞后代表了蒸发气体通过整个耀斑环的传播时间。 冷成分的EM比其模拟对应物小几倍，这表明可能由于环截面积的扩展或湍流波动导致传导冷却受到抑制。 冷成分的时间滞后和较小的EM比值为耀斑环的几何结构提供了重要的约束。 显示英文摘要

摘要： The Neutron star Interior Composition ExploreR (NICER) X-ray observatory observed two powerful X-ray flares equivalent to superflares from the nearby young solar-like star, kappa1 Ceti, in 2019. NICER follows each flare from the onset through the early decay, collecting over 30 cts s-1 near the peak, enabling a detailed spectral variation study of the flare rise. The flare in September varies quickly in ~800 sec, while the flare in December has a few times longer timescale. In both flares, the hard band (2-4 keV) light curves show typical stellar X-ray flare variations with a rapid rise and slow decay, while the soft X-ray light curves, especially of the September flare, have prolonged flat peaks. The time-resolved spectra require two temperature plasma components at kT ~0.3-1 keV and ~2-4 keV. Both components vary similarly, but the cool component lags by ~200 sec with a 4-6 times smaller emission measure (EM) compared to the hot component. A comparison with hydrodynamic flare loop simulations indicates that the cool component originates from X-ray plasma near the magnetic loop footpoints, which mainly cools via thermal conduction. The time lag represents the travel time of the evaporated gas through the entire flare loop. The cool component has several times smaller EM than its simulated counterpart, suggesting a suppression of conductive cooling possibly by the expansion of the loop cross-sectional area or turbulent fluctuations. The cool component's time lag and small EM ratio provide important constraints on the flare loop geometry.