Changing-look Event in NGC 3516: Continuum or Obscuration Variability?

Mehdipour, M.; Kriss, G. A.; Brenneman, Laura; Costantini, E.; Kaastra, J. S.; Branduardi‐Raymont, G.; Gesu, Laura Di; Ebrero, J.; Mao, Junjie

doi:10.3847/1538-4357/ac42ca

Cited by 22 publications

(28 citation statements)

References 94 publications

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“…We find that an additional absorption component is needed besides the Galactic absorption. We adopt an absorbed power-law model or an absorbed reflected power-law model in this work, where NH is fixed in our fitting because that there is no strong evidence for variable absorption during variability (e.g., Huerta et al 2014;Mehdipour et al 2022). The narrow Fe Kα line components are evident in all observations (see Figure 5).…”

Section: The X-ray Spectral Evolution In Clagnsmentioning

confidence: 99%

Coevolution of Broad Emission Lines and X-Ray Spectrum in Changing-look AGNs

Liu

Lyu

2022

ApJ

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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 2–10 keV/L Edd, normally follow negative and positive correlations when the Eddington ratio is lower and higher than a critical value of ∼10−3. We find that the CLAGNs observed with broad Hβ emission lines stay in the positive part of the Γ–L 2–10 keV/L Edd correlation, while the broad Hβ lines become weak or disappear in the anticorrelation part of the Γ–L 2–10 keV/L 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 bol–L bol/L Edd correlation. These results support that the CLAGNs belong to a special stage of AGNs with a bolometric Eddington ratio ∼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.

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Section: The X-ray Spectral Evolution In Clagnsmentioning

confidence: 99%

Coevolution of Broad Emission Lines and X-Ray Spectrum in Changing-look AGNs

Liu

Lyu

2022

ApJ

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“…Our studies of the intrinsic continuum in NGC 5548 (Mehdipour et al 2015(Mehdipour et al , 2016, as well as NGC 3783 (Mehdipour et al 2017) and NGC 3227 (Mehdipour et al 2021), show that during the obscuration epochs changes in the continuum parameters and the luminosities are moderate and typical of a Seyfert-1 galaxy. This is in contrast to some changing-look AGN, such as NGC 3516 (Mehdipour et al 2022), where the optical/UV emission from the disk and the X-ray emission from the corona have both undergone major transformations. Thus, spectral changes in the obscured UV and optical continuum, as well as the BLR emission lines, underwent significant dimming (Crenshaw et al 2003;Kriss et al 2019a).…”

Section: Modeling Of the Obscuring Windmentioning

confidence: 74%

10 Yr Transformation of the Obscuring Wind in NGC 5548

Mehdipour¹,

Kriss²,

Costantini³

et al. 2022

ApJL

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A decade ago, the archetypal Seyfert-1 galaxy NGC 5548 was discovered to have undergone major spectral changes. The soft X-ray flux had dropped by a factor of 30 while new broad and blueshifted UV absorption lines appeared. This was explained by the emergence of a new obscuring wind from the accretion disk. Here we report on the striking long-term variability of the obscuring disk wind in NGC 5548 including new observations taken in 2021–2022 with the Swift Observatory and the Hubble Space Telescope’s Cosmic Origins Spectrograph. The X-ray spectral hardening as a result of obscuration has declined over the years, reaching its lowest in 2022, at which point we find the broad C iv UV absorption line to have nearly vanished. The associated narrow low-ionization UV absorption lines, produced previously when shielded from the X-rays, are also remarkably diminished in 2022. We find a highly significant correlation between the variabilities of the X-ray hardening and the equivalent width of the broad C iv absorption line, demonstrating that X-ray obscuration is inherently linked to disk winds. We derive for the first time a relation between the X-ray and UV covering fractions of the obscuring wind using its long-term evolution. The diminished X-ray obscuration and UV absorption are likely caused by an increasingly intermittent supply of outflowing streams from the accretion disk. This results in growing gaps and interstices in the clumpy disk wind, thereby reducing its covering fractions.

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“…The fraction of blueshifted broad line Hβ with ∆v + 3σ(∆v) < 0 is about 14% for quasars in Hu et al (2008), and these blueshifted quasars may be explained by additional blueshift of a kinematic origin arising from radial motion, e.g., outflows. Outflows seem exist even if AGNs are during theirs low-flux states (e.g., Mehdipour et al 2022). Larger quasar sample, e.g., SDSS DR7 quasars in Liu et al (2019) who gave the detailed parameters of spectra, will be used in the next work.…”

Section: Discussionmentioning

confidence: 99%

Measuring the Virial Factor in SDSS DR5 Quasars with Redshifted H$β$ and Fe ii Broad Emission Lines

Liu,

Feng,

et al. 2022

Preprint

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Under the hypothesis of gravitational redshift induced by the central supermassive black hole, and based on line widths and shifts of redward shifted Hβ and Fe ii broad emission lines for a sample of 1973 z < 0.8 SDSS DR5 quasars, we measured the virial factor in determining supermassive black hole masses, usually estimated by the reverberation mapping (RM) method or the relevant secondary methods. The virial factor had been believed to be from the geometric effect of broad-line region. The measured virial factor of Fe ii is larger than that of Hβ for 98% of these quasars. The virial factor is very different from object to object and for different emission lines. For most of these quasars, the virial factor of Hβ is larger than these averages that were usually used in determining the masses of black holes. There are three positive correlations among the measured virial factor of Hβ, dimensionless accretion rate and Fe ii/Hβ line ratio. A positive three-dimensional correlation is found among these three quantities, and this correlation indicates that the virial factor is likely dominated by the dimensionless accretion rate and metallicity. A negative correlation is found between the redward shift of Hβ and the scaled size of broad-line region radius in units of the gravitational radius of black hole. This negative correlation will be expected naturally if the redward shift of Hβ is mainly from the gravity of black hole. Radiation pressure from accretion disk may be a significant contributor to the virial factor.Subject headings: Active galactic nuclei (16) -Black hole physics (159) -Emission line galaxies (459) -Quasars (1319) -Supermassive black holes (1663)

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Changing-look Event in NGC 3516: Continuum or Obscuration Variability?

Cited by 22 publications

References 94 publications

Coevolution of Broad Emission Lines and X-Ray Spectrum in Changing-look AGNs

Coevolution of Broad Emission Lines and X-Ray Spectrum in Changing-look AGNs

10 Yr Transformation of the Obscuring Wind in NGC 5548

Measuring the Virial Factor in SDSS DR5 Quasars with Redshifted H$β$ and Fe ii Broad Emission Lines

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