More than softer-when-brighter: The X-ray powerlaw spectral variability in NGC 4051

作     者：Yun-Jing Wu Jun-Xian Wang Zhen-Yi Cai Jia-Lai Kang Teng Liu Zheng Cai Yun-Jing Wu;Jun-Xian Wang;Zhen-Yi Cai;Jia-Lai Kang;Teng Liu;Zheng Cai

作者机构：CAS Key Laboratory for Research in Galaxies and CosmologyDepartment of AstronomyUniversity of Science and Technology of ChinaHefei 230026China School of Astronomy and Space ScienceUniversity of Science and Technology of ChinaHefei 230026China Department of AstronomyTsinghua UniversityBeijing 100084China Max-Planck-Institut für Extraterrestrische PhysikGarching bei Munchen D-85748Germany 

出 版 物：《Science China(Physics,Mechanics & Astronomy)》 (中国科学：物理学、力学、天文学（英文版）)

年 卷 期：2020年第63卷第12期

页      面：102-112页

核心收录：

学科分类：07[理学] 070302[理学-分析化学] 070401[理学-天体物理] 0703[理学-化学] 0704[理学-天文学] 

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.11421303,11890693,and 12033006) CAS Frontier Science Key Research Program(Grant No.QYZDJ-SSW-SLH006) 

主　　题：active galaxies X-ray Seyfert galaxies 

摘      要：The powerlaw X-ray spectra of active galactic nuclei at moderate to high accretion rates normally appear softer when they brighten,for which the underlying mechanisms are yet *** XMM-Newton observations and excluding photons2 keV to avoid contamination from the soft excess,in this work we scrutinize the powerlaw spectral variability of NCG 4051 from two new *** first find that a best-fitsofter-when-brighterrelation is statistically insufficient to explain the observed spectral variabilities,and intervals deviated from the empirical relation are clearly visible in the light curve of 2-4 ke V/4-10 keV count rate *** deviations are seen not only between but also within individual XMM-Newton exposures,consistent with random variations of the corona geometry or inner structure(with timescales as short as^1 ks),in addition to those behind the smoothsofter-when-brighter*** further find thesofter-when-brightertrend gradually weakens with the decreasing timescale(from^100 ks down to 0.5 ks).These findings indicate that the powerlaw spectral slope is not solely determined by its *** propose a two-tier geometry,including flares/nano-flares on top of the inner disc and an embedding extended corona(heated by the flares,in analogy to solar corona)to explain the observations together with other observational clues in *** spectral variabilities could be due to individual flares/nano-flares,while slow ones are driven by the variations in the global activity of inner disc region(akin to the variation of solar activity,but not the accretion rate)accompanied with heating/cooling and inflation/contraction of the extended corona.