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arXiv 1605.08041astro-ph.HE
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NGC 7674中康普顿厚度AGN的弱中性Fe荧光线和长时X射线演化

The weak neutral Fe fluorescence line and long-term X-ray evolution of the Compton-thick AGN in NGC 7674

P. Gandhi, A. Annuar, G. B. Lansbury, D. Stern, D. M. Alexander, F. E. Bauer, S. Bianchi, S. E. Boggs, P. G. Boorman, W. N. Brandt, M. Brightman, F. E. Christen… 展开作者

P. Gandhi, A. Annuar, G. B. Lansbury, D. Stern, D. M. Alexander, F. E. Bauer, S. Bianchi, S. E. Boggs, P. G. Boorman, W. N. Brandt, M. Brightman, F. E. Christensen, A. Comastri, W. W. Craig, A. Del Moro, M. Elvis, M. Guainazzi, C. J. Hailey, F. A. Harrison, M. Koss, I. Lamperti, G. Malaguti, A. Masini, G. Matt, S. Puccetti, C. Ricci, E. Rivers, D. J. Walton, W. W. Zhang

摘要:

利用$NuSTAR$ X射线方法对NGC 7674活动星系核进行了观测。该源显示出平坦的X射线光谱,表明它被康普顿厚度的气体柱所掩盖。基于长期的通量变暗,以前的工作提出了另一种可能性,即源是一个最近关闭的活动星系核,观测到的X射线是来自环面的滞后回波。我们的高质量数据显示,在硬X射线中,源以反射为主,但具有相对较弱的中性Fe K $α$发射线(等效宽度[EW]为$\approx$ 0.4 keV)和较强的Fe XXVI电离线(EW $\approx$ 0.2 keV)。我们建立了一个更新的长期X射线光变曲线的NGC 7674,发现所观察到的2-10 keV的流量一直保持不变,在过去的$\approx$ 20年,高通量状态探测$Ginga$。光的传播时间参数限制反射器的最小半径为$\sim$ 3.2 pc下关闭AGN的情况下,$\approx$ 30倍以上的预期尘埃升华半径,使这种可能性不大。一个不完整的康普顿厚活动星系核(CTGN)的解是合理的,目前需要的最小视线柱密度($N_{\rm H}$)为3 $\times$ 10 $^{24}$ cm $^{-2}$,并产生一个2-10 keV的本征光度(3-5)$\times$ 10 $^{43}$ erg s $^{-1}$。实际不确定度范围为$\approx$(1-13)$\times$ 10 $^{43}$ erg s $^{-1}$。该源具有最弱的荧光线之间{ \em善意} CTAGN,并可能是一个本地模拟的辐射热发光系统显示复杂的中性和电离铁发射。它阐明了识别的困难和适当的表征的基础上的中性Fe K PDMATHAMN线的强度远CTGN。

英文摘要:

We present $NuSTAR$ X-ray observations of the active galactic nucleus (AGN) in NGC 7674. The source shows a flat X-ray spectrum, suggesting that it is obscured by Compton-thick gas columns. Based upon long-term flux dimming, previous work suggested the alternate possibility that the source is a recently switched-off AGN with the observed X-rays being the lagged echo from the torus. Our high-quality data show the source to be reflection-dominated in hard X-rays, but with a relatively weak neutral Fe K$α$ emission line (equivalent width [EW] of $\approx$ 0.4 keV) and a strong Fe XXVI ionised line (EW $\approx$ 0.2 keV). We construct an updated long-term X-ray light curve of NGC 7674 and find that the observed 2-10 keV flux has remained constant for the past $\approx$ 20 years, following a high flux state probed by $Ginga$. Light travel time arguments constrain the minimum radius of the reflector to be $\sim$ 3.2 pc under the switched-off AGN scenario, $\approx$ 30 times larger than the expected dust sublimation radius, rendering this possibility unlikely. A patchy Compton-thick AGN (CTAGN) solution is plausible, requiring a minimum line-of-sight column density ($N_{\rm H}$) of 3 $\times$ 10$^{24}$ cm$^{-2}$ at present, and yields an intrinsic 2-10 keV luminosity of (3-5) $\times$ 10$^{43}$ erg s$^{-1}$. Realistic uncertainties span the range of $\approx$ (1-13) $\times$ 10$^{43}$ erg s$^{-1}$. The source has one of the weakest fluorescence lines amongst {\em bona fide} CTAGN, and is potentially a local analogue of bolometrically luminous systems showing complex neutral and ionised Fe emission. It exemplifies the difficulty of identification and proper characterisation of distant CTAGN based on the strength of the neutral Fe K$α$ line.

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