发表机构
Montana State University; University of Leicester; Inter-University Centre for Astronomy and Astrophysics; The University of Tokyo（蒙大拿州立大学; 莱斯特大学; 大学间天体物理中心; 东京大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用NICER分析SAX J1808.4-3658两次爆发的X射线光谱，发现~1 keV软X射线特征随源亮度变化，与吸积过程耦合，两次爆发间再处理体密度差异可解释特征强度和形态的不同，为该特征起源提供了更严格约束。
AI 中文摘要
我们利用NICER对吸积毫秒脉冲星SAX J1808.4-3658在2019年和2022年的爆发进行了系统的X射线光谱分析，重点关注存在已久的~1 keV光谱特征的本质。我们报告了首个明确证据，表明0.9-1.0 keV特征随源亮度呈系统性变化，与连续谱和黑体流量均呈现强相关性，这证实该特征与吸积过程直接耦合。该特征的标度和能量分布在两次爆发间存在差异，对应再处理体密度发生了约2个数量级的变化（2019年的电子数密度log n_e≈19.1，2022年约为17.3），这自然解释了2019年更强、更宽的特征，以及2022年更弱、更局域化的~1 keV特征，与高密度反射模型相符。这些结果为确定SAX J1808.4-3658中~1 keV特征的起源提供了迄今为止最严格的约束。
英文摘要
We present a systematic X-ray spectral analysis of the 2019 and 2022 outbursts of the accreting millisecond pulsar SAX J1808.4-3658 with extit{NICER} with a particular emphasis on the nature of the longstanding $\sim$1\,keV spectral feature. We report here the first clear evidence that the 0.9-1.0 keV feature varies systematically with source brightness, exhibiting strong correlations with both continuum and blackbody flux. This establishes that the feature is directly coupled to the accretion process. The scaling and energy distribution of the feature differ between outbursts, corresponding to a $\sim$2\,dex change in reprocessor density (log\,$n_e \approx 19.1$ in 2019 vs. $\sim$17.3 in 2022), which naturally explains the stronger, broader feature in 2019 and the weaker, more localized $\sim$1\,keV feature in 2022, in agreement with high-density reflection models. These results provide the strongest constraints to date on the origin of the $\sim$1\,keV feature in SAX J1808.4-3658.
CommentsAccepted to ApJ
