标题： 蟹状星云超新星遗迹的小尺度X射线变化 显示英文标题

标题： Small-Scale X-ray Variability in the Cassiopeia A Supernova Remnant

摘要： X射线观测结果的比较显示，使用钱德拉ACIS-S3在2000年、2002年和2004年对仙后座A超新星遗迹的观测揭示了几个小尺度特征（<= 10角秒），这些特征在四年时间范围内显示出显著的强度变化。 在此我们报告了六个特征的变异性，其中四个特征的计数率增加了约10%至超过90%，另外两个特征的计数率减少了约30% - 40%。 虽然提取的1-4.5 keV X射线光谱没有显示出发射线强度的明显变化，但使用非平衡电离、富含金属的等离子体模型进行的光谱拟合表明，计数率增加的特征电子温度升高，而计数率减少的特征电子温度降低。 基于观测到的计数率变化以及假设自由膨胀的抛射物在反向激波前的速度约为5000 km/s，我们估计未受冲击的抛射物的空间尺度变化为0.02 - 0.03 pc，这与X射线发射的抛射物属于比光学发射抛射物更弥散的成分一致，后者空间尺度约为0.001 pc。 显示英文摘要

摘要： A comparison of X-ray observations of the Cassiopeia A supernova remnant taken in 2000, 2002, and 2004 with the Chandra ACIS-S3 reveals the presence of several small scale features (<= 10 arcsec) which exhibit significant intensity changes over a 4 year time frame. Here we report on the variability of six features, four of which show count rate increases from ~ 10% to over 90%, and two which show decreases of ~ 30% -- 40%. While extracted 1-4.5 keV X-ray spectra do not reveal gross changes in emission line strengths, spectral fits using non-equilibrium ionization, metal-rich plasma models indicate increased or decreased electron temperatures for features showing increasing or decreasing count rates, respectively. Based on the observed count rate changes and the assumption that the freely expanding ejecta has a velocity of ~ 5000 km/s at the reverse shock front, we estimate the unshocked ejecta to have spatial scale variations of 0.02 - 0.03 pc, which is consistent with the X-ray emitting ejecta belonging to a more diffuse component of the supernova ejecta than that seen in the optically emitting ejecta, which have spatial scales ~ 0.001 pc.