发表机构
The University of Utah; NASA Goddard Space Flight Center; The University of Virginia; California Institute of Technology; Wayne State University; Arizona State University; Space Telescope Science Institute; NASA Marshall Space Flight Center（犹他大学; 美国国家航空航天局戈达德太空飞行中心; 弗吉尼亚大学; 加州理工学院; 韦恩州立大学; 亚利桑那州立大学; 太空望远镜科学研究所; 美国国家航空航天局马歇尔太空飞行中心）
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NuSTAR和XMM-Newton在JWST北黄极时域场的巡天数据，首次对52个源进行光谱建模并对112个源进行变化研究，发现约1000计数和多个历元可探测变化，且$N_H$变化在长时标上略常见，环面对微弱AGN变化驱动作用有限。
AI 中文摘要
作为硬X射线波段首批深度时域巡天之一，JWST北黄极时域场（NEP-TDF）中的NuSTAR观测活动为测量中高红移宇宙中微弱活动星系核（AGN）群体的变化提供了绝佳机会。在X射线波段，AGN的变化通常由日冕亮度变化（$F_{int}$变化）或SMBH附近遮蔽物质柱密度的变化（$N_H$变化）引起。需要宽带光谱（约0.5-24 keV）才能可靠地区分这两种现象。凭借NuSTAR和XMM-Newton的同时覆盖——以及1.8 Ms的Chandra监测——NEP-TDF中的X射线巡天非常适合这一目的。这项工作首次对活动后半期发现的52个NuSTAR识别源进行了光谱建模，并对整个112个源的NuSTAR NEP-TDF星表进行了光谱变化研究。识别出七个变化候选体。我们发现，需要分散在多个（约10个）历元中的约1000个总计数才能探测到变化。此外，将变化源与巡天灵敏度进行比较，以告知种群合成模型变化如何影响微弱AGN的可探测性，这些微弱AGN主导着SMBH吸积历史。最后，研究了$N_H$变化的时间尺度作为遮蔽物位置的探针。显著变化在大于100天的时间尺度上略更常见，这表明在微弱AGN中，环面可能仅对驱动$N_H$变化有轻微主导作用。
英文摘要
As one of the first deep time-domain surveys in the hard X-ray band, the NuSTAR campaign in the JWST North Ecliptic Pole Time Domain Field (NEP-TDF) offers a prime opportunity to measure variability in a faint population of Active Galactic Nuclei (AGN) in the medium-to-high redshift universe. In the X-ray band, AGN variability is generally caused by changes in the brightness of the corona ($F_{int}$ variability) or changes in the column density of obscuring material near the SMBH ($N_H$ variability). Broad-band spectroscopy ($\sim$0.5-24 keV) is required to reliably disentangle these two phenomena. With simultaneous NuSTAR and XMM-Newton coverage---as well as 1.8 Ms of Chandra monitoring---the X-ray surveys in the NEP-TDF are ideally situated for this purpose. This work presents the first spectral modeling of the 52 NuSTAR-identified sources discovered in the latter half of the campaign, as well as a spectroscopic variability study of the entire 112-source NuSTAR NEP-TDF catalog. Seven variable candidates are identified. We find that $\gtrsim 1000$ total counts split across many ($\gtrsim 10$) epochs are needed in order to detect variability. Additionally, variable sources are compared to the survey sensitivity in order to inform population synthesis models of how variations can affect the detectability of faint AGN, which dominate the SMBH accretion history. Lastly, the timescale of $N_H$ variability is investigated as a probe for the obscurer location. Significant variability is slightly more common on $> 100$ day timescales, suggesting that the torus may have only slight dominance in driving $N_H$ variability in faint AGN.
Comments36 pages, 13 figures; accepted by ApJ
