X-ray spectroscopy offers an opportunity to study the complex mixture of emitting and absorbing components in the circumnuclear regions of active galactic nuclei, and to learn about the accretion process that fuels AGN and the feedback of material to their host galaxies. We describe the spectral signatures that may be studied and review the X-ray spectra and spectral variability of active galaxies, concentrating on progress from recent Chandra, XMM-Newton and Suzaku data for local type 1 AGN. We describe the evidence for absorption covering a wide range of column densities, ionization and dynamics, and discuss the growing evidence for partial-covering absorption from data at energies > 10 keV. Such absorption can also explain the observed X-ray spectral curvature and variability in AGN at lower energies and is likely an important factor in shaping the observed properties of this class of source. Consideration of self-consistent models for local AGN indicates that X-ray spectra likely comprise a combination of absorption and reflection effects from material originating within a few light days of the black hole as well as on larger scales. It is likely that AGN X-ray spectra may be strongly affected by the presence of disk-wind outflows that are expected in systems with high accretion rates, and we describe models that attempt to predict the effects of radiative transfer through such winds, and discuss the prospects for new data to test and address these ideas.
The cosmic X-ray background (XRB) spectrum and active galaxy number counts encode essential information about the spectral evolution of active galactic nuclei (AGNs) and have been successfully modeled by XRB synthesis models for many years. Recent measurements of the $8$--$24$ keV AGN number counts by NuSTAR and Swift-BAT are unable to be simultaneously described by existing XRB synthesis models, indicating a fundamental breakdown in our understanding of AGN evolution. Here we show that the $8$--$24$ keV AGN number counts can be successfully modeled with an XRB synthesis model in which the ref…
The X-ray spectra of active galactic nuclei (AGNs) often exhibit an excess of emission above the primary power-law at energies <~ $2$ keV. Two models for the origin of this `soft excess' are ionized relativistic reflection from the inner accretion disc and Comptonization of thermal emission in a warm corona. Here, we introduce reXcor, a new AGN X-ray ($0.3$-$100$ keV) spectral fitting model that self-consistently combines the effects of both ionized relativistic reflection and the emission from a warm corona. In this model, the accretion energy liberated in the inner disc is distributed betwee…
A direct comparison of X-ray spectral models for tori in active galactic nuclei
活动星系核中环面的X射线谱模型可以用来限制环面的性质,但是这些模型的准确性还没有得到验证。我们最近使用Geant 4构建了一个用于环面的代码,它可以轻松处理不同的几何形状(Liu & Li 2014)。因此,我们采用与Murphy & Yaqoob(2009,以下简称MY09)和Bennman & Nandra(2011,以下简称BN11)相同的假设,并尝试重现它们的光谱。结果表明,对于$\NH=10^{24}$和$10^{25}$ cm $^{-2}$,我们能很好地再现MY09的Fe K $α$线的反射光谱和强度。然而,我们不能产生BN 11在低能带的强反射分量。该分量的来源是来自环面可见内壁的反射,并且在BN 11的几何形状下,它在边缘方向上应该非常弱。因此,BN11中反射光谱的行为与其几何形状不一致。BN 11的Fe K $α$线的强度也不同于我们的结果和光学薄情况下的分析结果。谱模型的局限性会使X射线谱拟合的参数产生偏差。
We use the publicly available XMM-Newton archive to select a sample of 20 active galactic nuclei (AGN) known to exhibit reverberation signatures caused by the reflection of X-rays from the corona off the accretion disc that feeds the central black hole engine. Inverse Compton scattering by energetic electrons, coupled with accretion disc fluctuations give rise to the highly variable observed X-ray spectrum, the behaviour of which is still not fully understood. We use 121 observations in 3 - 4 distinct spectral states for each source and calculate the time lags as a function of frequency. We fi…
We explore a disc origin for the highly-blueshifted, variable absorption lines seen in the X-ray spectrum of the Narrow Line Seyfert 1 galaxy IRAS13224-3809. The blueshift corresponds to a velocity of about 0.25c. Such features in other Active Galactic Nuclei are often interpreted as UltraFast Outflows (UFOs). The velocity is of course present in the orbital motions of the inner disk. The absorption lines in IRAS13224-3809 are best seen when the flux is low and the reflection component of the disk is strong relative to the power-law continuum. The spectra are consistent with a model in which t…
A Comparison of Two Methods for Estimating Black Hole Spin in Active Galactic Nuclei
角动量,或自旋,是黑洞(BH)的一个基本属性,但它比质量或吸积率(对于活跃吸积系统)更难估计。近年来,高质量的X射线观测已经允许详细测量Fe K $α$发射线,其中相对论谱线展宽允许对自旋参数进行限制(X射线反射法)。另一种方法使用吸积盘模型来拟合活动星系核的连续辐射(连续拟合法,简称CF法)。虽然每种技术都有依赖于模型的不确定性,但这些都是目前可用的最佳经验工具,应该在两种技术都可以应用的系统中进行审查。对这两种方法的详细比较也是有用的,因为这两种方法都不能适用于所有活动星系核。X射线反射技术主要针对局部(z $\lesssim$ 0.1)系统,而CF方法可以应用于更高的红移,达到和超过活动星系核活动和生长的峰值。在这里,我们应用CF方法与X射线反射测量两个活动星系核。对于高质量活动星系核H1821+643和Seyfert 1 NGC 3783,我们发现了一个与X射线反射测量一致的自旋参数范围。然而,如果我们在模型中加入盘风,NGC 3783的反射方法所支持的接近最大自旋的可能性更大。这些技术的改进,再加上改进的X射线测量和更严格的BH质量约束,将允许在更大的样本AGN的这种比较,并增加我们的信心,这些自旋估计技术。
On the equivalent width of the Fe K$α$ line produced by a dusty absorber in active galactic nuclei
被遮蔽的活动星系核提供了一个研究围绕中心引擎的物质的机会。吸收体上的几何和物理约束可以从再处理的活动星系核辐射中推导出来。特别地,遮蔽气体可以再处理核X射线发射,产生窄的Fe K $α$线和康普顿反射峰。近年来,X射线从模糊环面反射的模型已经被计算出来;然而,尽管反射气体可能是尘埃,模型还没有考虑到尘埃对预测光谱的影响。我们研究这个问题,通过分析两组模型,有和没有灰尘的存在下,使用一维光电离代码多云。对一系列柱密度($22 <{\rm log}[N_H(\rm cm^{-2})]< 24.5$)和氢密度($6 <{\rm log}[n_H(\rm cm^{-3})]< 8$)进行计算。计算结果表明,尘埃的存在下,可以提高的Fe K $α$等效宽度(EW)在反射光谱的因素高达$\approx$ 8康普顿厚(CT)的气体和一个典型的ISM粒度分布。EW相对于反射连续谱的增强是由于由尘埃颗粒的各向异性散射行为引起的反射连续谱强度的降低。这种效应将是最相关的反射,从遥远的,主要是中性气体,是一个可能的解释活动星系核,显示出强大的Fe K $α$ EW和一个相对较弱的反射连续。我们的研究结果表明,它是一个重要的是要考虑到灰尘,而建模的X射线反射光谱,推断CT柱密度从观测到的Fe K $α$ EW可能并不总是有效的。需要多维度模型来充分探索影响的程度。
Both long and short gamma-ray bursts (GRBs) are expected to occur in the dense environments of active galactic nuclei (AGN) accretion disks. As these bursts propagate through the disks they live in, they photoionize the medium causing time-dependent opacity that results in transients with unique spectral evolution. In this paper we use a line-of-sight radiation transfer code coupling metal and dust evolution to simulate the time-dependent absorption that occurs in the case of both long and short GRBs. Through these simulations, we investigate the parameter space in which dense environments lea…
We present a spectral analysis of two XMM-Newton observations of the narrow-line Seyfert 1 galaxy UGC 11763. UGC 11763 shows very different soft X-ray spectral shapes in the two observations separated by 12 years. Three spectral models are considered to explain the multi-epoch X-ray variability of UGC 11763, one based on the relativistic disc reflection model, one based on multiple partially-covering absorbers combined with the warm corona model, and a hybrid model. In the first model, the X-ray variability of UGC 11763 is caused by the emission from a compact coronal region with a variable si…
The standard alpha-disc model predicts an anti-correlation between the density of the inner accretion disc and the black hole mass times square of the accretion rate, as seen in higher mass ($M_{\rm BH}>10^{6} M_{\odot}$) active galactic nuclei (AGNs). In this work, we test the predictions of the alpha-disc model and study the properties of the inner accretion flow for the low-mass end ($M_{\rm BH}\approx 10^{5-6}M_{\odot}$) of AGNs. We utilize a new high-density disc reflection model where the density parameter varies from $n_{\rm e}=10^{15}$ to $10^{20}$ cm$^{-3}$ and apply it to the broadba…
Reprocessed X-ray radiation carries important information about the structure and physical characteristics of the material surrounding the supermassive black hole (SMBH) in active galactic nuclei (AGN). We report here on a newly developed simulation platform, RefleX, which allows to reproduce absorption and reflection by quasi-arbitrary geometries. We show here the reliability of our approach by comparing the results of our simulations with existing spectral models such as pexrav, MYTorus and BNTorus. RefleX implements both Compton scattering on free electrons and Rayleigh scattering and Compt…
The condensation of the corona for the correlation between the hard X-ray photon index $Γ$ and the reflection scaling factor $\Re$ in active galactic nuclei
A three bright X-ray non-target sources are detected in the field of the seyfert 1 galaxy MKN 205. These sources are classified as optically Early-type galaxy, BLAGN, and NELG (NED, SIMBAD, and AXIS). The spectrum analysis is made for these objects using thermal models and non-thermal models, modified by interstellar absorption. In some objects we can not distinguish between the thermal and non-thermal models of the hard components from the spectrum alone. The presence of intrinsic absorption is tested by photoelectric absorption at the redshift of the sources, and we assumed the flux distribu…
We present the broadband (0.3-40.0 keV) X-ray analysis of a unique intermediate polar Paloma using simultaneous data from XMM-Newton and NuSTAR observatories. The X-ray power spectra show strong modulations over orbital period compared to spin period. The orbit folded lightcurves show single broad hump like structure with strong dips for soft to medium X-rays (0.3-10.0 keV). The energy dependent dips at $ϕ\sim 0.16$ and $0.5$ arise due to complex intrinsic absorber, strong enough to have effect well around 15 keV. The absorber could potentially be contributed from accretion curtain/ accretion …
Unveiling the X-ray/UV properties of disk winds in active galactic nuclei using broad and mini-broad absorption line quasars
本文对Palomar-Green类星体目录中的6个BAL类星体和7个mini-BAL类星体的46个XMM-Newton观测数据进行了统一分析。使用EPIC-pn进行中等质量的X射线光谱,并允许将一般源光谱形状描述为复杂的,显著偏离幂律发射。在不同能带中的简单幂律分析强烈地表明吸收在形成光谱方面比反射更重要。如果允许吸收气体部分覆盖连续谱发射源或被电离,则推断出$10^{22-24}$ cm $^{-2}$量级的大柱密度。当统计数据足够高时,几乎每一个源都被发现在不同的时间尺度上(从几年到几小时)有不同的光谱形状。总而言之,这些观测结果与辐射驱动的吸积盘风形成这些有趣的宇宙源的光谱是一致的。
X-ray reflection in oxygen-rich accretion discs of ultra-compact X-ray binaries
我们给出了两个候选超致密X射线双星4U~0614+091和4U~1543 $-$ 624的光谱X射线数据。我们使用2012年和2013年获得的{ \it XMM-牛顿}和{ \it钱德拉}观测结果确认了宽O VIII Ly $α$反射线(在$\approx18\ Å$)的存在。这些来源中的施主星是碳-氧或氧-氖-镁白矮星。因此,吸积盘富含氧,这使得O VIII Ly $α$线特别强。我们还证实了一个强大的吸收边在$\approx14$的存在,到目前为止,在文献中解释为由于中性氖在拱星和星际介质的吸收。然而,要获得一个很好的拟合到这个边缘所需的丰度是$\approx3-4$倍太阳,提出了一个问题,这种解释。此外,用假设太阳成分的模型对富含碳和氧、氢和氦贫乏的盘的X射线反射进行建模可能会使几个最佳拟合参数偏置。为了自洽地描述X射线反射谱,我们修改了现有的{ \sc xillver}反射模型。我们提出了初始网格,可以用来模拟X射线反射光谱的UCXB与富碳氧吸积盘。结果表明,与假设太阳丰度的反射模型相比,新的反射模型能更好地描述4U~0614+091和4U~1543 $-$ 624的反射谱.除了强O VIII Ly $α$线外,新的反射模型还显示出强O VIII K边缘(在$14.23$线处)。我们发现,在$\approx 14$的吸收边的数据中存在的O VIII K-边缘形成由于在吸积盘…
In a previous paper, one of us calculated iron K$α$ line profiles emitted from possible accretion disks around traversable wormholes as a first step to use X-ray reflection spectroscopy to search for astrophysical wormholes in active galactic nuclei. In the present paper, we extend that work and construct an XSPEC model for the whole relativistic reflection spectrum. We apply our model to XMM-Newton and NuSTAR observations of the supermassive object in MCG-6-30-15 and we check whether these observations prefer the hypothesis that the central body is a Kerr black hole or a traversable wormhole.…