Changing-look active galactic nuclei (CLAGNs) show the disappearance and reappearance of broad emission lines in a few years, which challenges the orientation-based AGN unification model. We reduce the X-ray data for five well-studied CLAGNs that show a strong change in broad emission lines in the past several decades. We find that the X-ray photon index, $Γ$, and the Eddington-scaled X-ray luminosity, $L_{\rm 2-10 keV}/L_{\rm Edd}$, normally follow negative and positive correlations when the Eddington ratio is lower and higher than a critical value of $\sim 10^{-3}$. We find that the CLAGNs observed with broad H$β$ emission lines stay in the positive part of the $Γ-L_{\rm 2-10 keV}/L_{\rm Edd}$ correlation, while the broad H$β$ lines become weak or disappear in the anticorrelation part of the $Γ-L_{\rm 2-10 keV}/L_{\rm Edd}$ correlation, which suggests that the evolution of the broad lines should be correlated with the evolution of the underlying accretion process. We further find that the CLAGNs are consistent with the other different types of AGNs in the $L_{\rm bol}-L_{\rm bol}/L_{\rm Edd}$ correlation. These results support that the CLAGNs are belong to a special stage of AGNs with a bolometric Eddington ratio $\sim$1\%, where the broad emission lines are easily affected by the strong variation in ionization luminosity that is caused by the transition of accretion modes.
First Observational Evidence for QPO-like Coevolution between Characteristic Damping Timescales and X-ray Time Lags among AGNs
School of Physics and Electronic Engineering, Hanjiang Normal University（汉江师范学院物理与电子工程学院）；Key Laboratory of Astroparticle Physics of Yunnan Province, Yunnan University（云南省天体物理重点实验室，云南大学）；Department of Astronomy, Yunnan University（云南大学天文系）
The discovery of changing-look active galactic nuclei (CLAGNs) with the significant change of optical broad emission lines (optical CLAGNs) and/or strong variation of line-of-sight column densities (X-ray CLAGNs) challenges the orientation-based AGN unification model. We explore mid-infrared (mid-IR) properties for a sample of 57 optical CLAGNs and 11 X-ray CLAGNs based on the {\it Wide-field Infrared Survey Explorer} ({\it WISE}) archive data. We find that Eddington-scaled mid-IR luminosities of both optical and X-ray CLAGNs stay just between low-luminosity AGNs (LLAGNs) and luminous QSOs. Th…
We present results of a long-term optical, UV and X-ray study of variability of the nearby changing-look (CL) Seyfert NGC 1566 which was observed with the Swift Observatory from 2007 to 2020. We summarize our previously published spectroscopic and photometric results and present new observations. We reported on the alteration in the spectral type of NGC 1566 in 2018 (REF1). Moreover, we focused on the exceptional postmaximum behavior after 2018 July, when all bands dropped with some fluctuations (REF2). We observed four significant re-brightenings in the post-maximum period. We have found diff…
Context: Variations in the mass accretion rate appear to be responsible for the rapid transitions in spectral type that are observed in increasingly more active galactic nuclei (AGNs). These objects are now labeled "changing-look" AGNs and are key objects for understanding the physics of accretion onto supermassive black holes. Aims: We aim to complement the analysis and interpretation of changing-look AGNs by modeling the polarization variations that can be observed, in particular, polarized-light echoes. Methods: We built a complex and representative model of an AGN and its host galaxy and r…
22 Newly Identified Repeating Changing-look AGNs and Evidence for Extreme Broad-line Region Breathing
Aryabhatta Research Institute of Observational Sciences (ARIES)（阿亚巴塔观测科学研究所）；Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences（中国科学院天体结构与演化重点实验室）
We analyze the X-ray, optical, and mid-infrared data of a "changing-look" Seyfert galaxy \sdssj15 at $z\simeq0.086$. Over a period of one decade (2009 - 2018), its broad H$α$ line intensity increased by a factor of $\sim$4. Meanwhile, the X-ray emission in 2014 as observed by \chandra\ was about five times brighter than that in 2010 by {\it Suzaku}, and the corresponding emissions in V-band, mid-infrared W1 band brighten by $\sim$ 0.18, 0.32 mag, respectively. Moreover, the absorption in X-rays is moderate and stable, i.e. ${\rm N_{H}}\sim 10^{21} {\rm cm^{-2}}$, but the X-ray spectrum becomes…
Two major challenges to unification schemes for active galactic nuclei (AGN) are the existence of Narrow-Line Seyfert 1s (NLS1s) and the existence of changing-look (CL) AGNs. AGNs can drastically change their spectral appearance in the optical (changing their Seyfert type) and/or in the X-ray region. We illustrate the CL phenomenon with our multi-wavelength monitoring of NGC 2617 and discuss its properties compared with NLS1s. There are few examples of CL NLS1s and the changes are mostly only in the X-ray region. It has been proposed that some of these could be cases of a tidal-disruption even…
The time-scales of the variabilities in changing look (CL) active galactic nuclei (AGNs) are usually at the order of years to tens of years (some of them are even shorter than one year), which are much shorter than the viscous timescale of a standard thin accretion disk. It implies that the variabilities of CL AGNs cannot be reproduced by varying the mass accretion rate of the thin disk. In this work, we employ a magnetic accretion disk-outflow model to calculate the inflow time of the disk predominantly driven by magnetic outflows. In this model, most angular momentum of the gas in the disk i…
We study the properties of the host galaxies of Changing-Look Active Galactic Nuclei (CL AGNs) with the aim of understanding the conditions responsible for triggering CL activity. We find that CL AGN hosts primarily reside in the so-called green valley that is located between spiral-like star-forming galaxies and dead ellipticals, implying that CL AGNs are activated during distinct periods of quenching and galaxy transformation processes. CL AGN hosts have low galaxy asymmetry indicators, suggesting that secular evolutionary processes (the influence of bars and spirals, and possibly minor merg…
The physical mechanism for triggering the changing-look phenomenon in active galactic nuclei (AGNs) is still unclear. We explore this issue based on the multi-wavelength spectral and flux variations for a changing-look AGN Mrk~1018 with long-term observations in the X-ray, optical/ultraviolet(UV), and radio bands. Both the optical and the X-ray emission experience rapid decay in changing-look phase during 2010--2015, where a re-flare appears in the optical/UV and X-ray bands. We find a time lag of $\sim 20 $ days of optical/UV behind X-ray variations in type 1.9 phase. The 5 GHz radio flux dec…
It is known that the blazar jet emissions are dominated by non-thermal radiation while the accretion disk jets are normally dominated by thermal emission. In this work, our aim is to study the connection between the two types of emission by investigating the correlation between the blazar emission line intensity property, which embodies the nature of accretion disk, and the $γ$-ray flux property, which is the representative of jet emission. We compiled a sample of 656 blazars with available emission line equivalent widths ($EW$), the GeV $γ$-ray flux, and the SED information from the literatur…
Here we report an identification of B3\,0749+460A as a new double-peaked local "changing-look" active galactic nucleus (CL-AGN) in terms of our multi-epoch spectroscopic analysis. By comparing our new spectra taken in 2021 with the ones taken by the Sloan Digital Sky Survey in 2004, BOSS in 2013, and MaNGA in 2016, we reveal type transitions of Seyfert (Sy) 1.9$\rightarrow$Sy1.8$\rightarrow$Sy1.9. In the transitions, the classical broad H$α$ emission fades away since 2013, and disappears in our 2021 spectrum, although the absence of broad H$β$ can be traced back to at least 2016. A follow-up o…
We present new measurements of the evolution of the X-ray luminosity functions (XLFs) of unabsorbed and absorbed Active Galactic Nuclei (AGNs) out to z~5. We construct samples containing 2957 sources detected at hard (2-7 keV) X-ray energies and 4351 sources detected at soft (0.5-2 keV) energies from a compilation of Chandra surveys supplemented by wide-area surveys from ASCA} and ROSAT. We consider the hard and soft X-ray samples separately and find that the XLF based on either (initially neglecting absorption effects) is best described by a new flexible model parametrization where the break …
Discovery of ultra-fast outflows with v$_{\rm out}>0.3 \rm c$ in local bright active galactic nuclei
Università di Bologna（博洛尼亚大学）；INAF – OAS, Osservatorio di Astrofisica e Scienza dello Spazio Bologna（意大利国家天体物理研究所-波伦亚天文与空间科学观测站）；European Space Agency (ESA)（欧洲航天局）；European Space Research and Technology Centre (ESTEC)（欧洲航天研究与技术中心）；INAF – Osservatorio Astronomico di Roma（意大利国家天体物理研究所-罗马天文台）；INAF – Istituto di Astrofisica e Planetologia Spaziali（意大利国家天体物理研究所-空间天体物理学与行星科学研究所）；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）
The nature of the rare "Changing-look" (CL) phenomenon in active galactic nuclei (AGNs) is still under debate at current stage. We here present \it Swift/\rm XRT and UVOT follow-up observations of UGC\,3223, a newly discovered repeat CL-AGN with type transitions of $\mathrm{S1.5\rightarrow S2 \rightarrow S1.8}$ occurring in a period of about 30 years. By comparing the values previously reported in the \it ROSAT \rm All-sky Survey and in the second Swift-XRT Point Source catalog, we clearly find that the X-ray flux tightly follows the optical spectral transition, in which a spectral type closer…
NGC 5273 is a known optical and X-ray variable AGN. We analyze new and archival IR, optical, UV, and X-ray data in order to characterize its long-term variability from 2000 to 2022. At least one optical changing-look event occurred between 2011 and 2014, when the AGN changed from a Type 1.8/1.9 Seyfert to a Type 1. It then faded considerably at all wavelengths, followed by a dramatic but slow increase in UV/optical brightness between 2021 and 2022. Near-IR (NIR) spectra in 2022 show prominent broad Paschen lines that are absent in an archival spectrum from 2010, making NGC 5273 one of the few …
Radiation Pressure Instability in the "turn-on" Changing-Look AGN SDSS J1430+2303
Wuhan University（武汉大学）；Czech Academy of Sciences（捷克科学院）；Polish Academy of Sciences（波兰科学院）；University of Geneva（日内瓦大学）；Universidad Diego Portales（迭戈·波特莱斯大学）；Peking University（北京大学）；Zhejiang University（浙江大学）
X-ray eclipse tomography: Resolving the extent of X-ray-emitting region(s) in the Seyfert galaxy ESO362-G18
Universidad de Alcalá（阿尔卡拉大学）；Universidad Complutense de Madrid（马德里康普顿斯大学）；Foundation for Research and Technology-Hellas（希腊研究与技术基金会）；CSIC-INTA（西班牙国家科学技术研究中心-国家航空航天技术研究所）
We have studied the nature and origin of the soft X-ray excess detected in the interesting changing-look AGN (CLAGN) Mrk~590 using two decades of multi-wavelength observations from \xmm{}, \suzaku{}, \swift{} and \nustar{}. In the light of vanishing soft excess in this CLAGN, we test two models, "the warm Comptonization" and "the ionized disk reflection" using extensive UV/X-ray spectral analysis. Our main findings are: (1) the soft X-ray excess emission, last observed in 2004, vanished in 2011, and never reappeared in any of the later observations, (2) we detected a significant variability ($…
Accreting supermassive black holes (SMBHs) can exhibit variable emission across the electromagnetic spectrum and over a broad range of timescales. The variability of active galactic nuclei (AGNs) in the ultraviolet and optical is usually at the few tens of per cent level over timescales of hours to weeks. Recently, rare, more dramatic changes to the emission from accreting SMBHs have been observed, including tidal disruption events, 'changing look' AGNs and other extreme variability objects. The physics behind the 're-ignition', enhancement and 'shut-down' of accretion onto SMBHs is not entire…
We present a detailed timing and spectral study of an extremely variable narrow-line Seyfert~1 galaxy NGC 4748 using observations in the year 2017 and 2014 performed with AstroSat and XMM-Newton, respectively. Both observations show extremely variable soft and hard X-ray emission that are correlated with each other. In the 2014 data set, the source retains its general behaviour of "softer when brighter" while the 2017 observation exhibits a "harder when brighter" nature. Such changing behaviour is rare in AGNs and is usually observed in the black hole binary systems. The "harder when brighter"…
A break in the X-ray loudness of Markarian 590: evidence for an AGN spectral state transition?
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（尼古拉·哥白尼天文中心，波兰科学院）；DARK, Niels Bohr Institute, University of Copenhagen（DARK，哥本哈根大学尼尔斯·玻尔研究所）；Steward Observatory and Department of Astronomy, University of Arizona（亚利桑那大学斯图尔德天文台和天文学系）；Bishop’s University, Department of Physics & Astronomy（主教大学物理与天文学系）；Inter-University Centre for Astronomy and Astrophysics（大学间天文与天体物理中心）
Extreme Variability Reveals How the Eddington Ratio Regulates Coronal Power in Active Galactic Nuclei
SRM University-AP（SRM大学阿帕分校）；University of Geneva（日内瓦大学）；Universidad Diego Portales（迭戈·波特莱斯大学）；Peking University（北京大学）；Universidad de Tarapacá（塔拉帕卡大学）；Liège Université（列日大学）；Universiteit Gent（根特大学）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿基米德天体物理研究所）；Tel Aviv University（特拉维夫大学）；INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（意大利国家天体物理研究所博洛尼亚天文与空间科学观测站）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）
