AGN Variability

A number of monitoring observations of continuum emission from Active Galactic Nuclei (AGNs) have been made in optical-X-ray bands. The results obtained so far show (i) random up and down on timescales longer than decades, (ii) no typical timescales of variability on shorter timescales and (iii) decreasing amplitudes as timescales become shorter. The second feature indicates that any successful model must produce a wide variety of shot-amplitudes and -durations over a few orders in their light curves. In this sense, we conclude that the disk instability model is favored over the starburst model, since fluctuations on days are hard to produce by the latter model.Inter-band correlations and time lags also impose great constraints on models. Thus, constructing wavelength and time dependent models remains as future work.

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Liverpool-Maidanak monitoring of the Einstein Cross in 2006–2019

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037902 ◽

2020 ◽

Vol 637 ◽

pp. A89 ◽

Cited By ~ 1

Author(s):

L. J. Goicoechea ◽

B. P. Artamonov ◽

V. N. Shalyapin ◽

A. V. Sergeyev ◽

O. A. Burkhonov ◽

...

Keyword(s):

Active Galactic Nuclei ◽

Emission Scenario ◽

Galactic Nuclei ◽

Compact Object ◽

Light Curves ◽

Continuum Emission ◽

Emission Sources ◽

Uv Emission ◽

Source Radius

Quasar microlensing offers a unique opportunity to resolve tiny sources in distant active galactic nuclei and study compact object populations in lensing galaxies. We therefore searched for microlensing-induced variability of the gravitationally lensed quasar QSO 2237+0305 (Einstein Cross) using 4374 optical frames taken with the 2.0 m Liverpool Telescope and the 1.5 m Maidanak Telescope. These gVrRI frames over the 2006–2019 period were homogeneously processed to generate accurate long-term multi-band light curves of the four quasar images A–D. Through difference light curves, we found strong microlensing signatures. We then focused on the analytical modelling of two putative caustic-crossing events in image C, finding compelling evidence that this image experienced a double caustic crossing. Additionally, our overall results indicate that a standard accretion disc accounts reasonably well for the brightness profile of UV continuum emission sources and for the growth in source radius when the emission wavelength increases: Rλ ∝ λα, α = 1.33 ± 0.09. However, we caution that numerical microlensing simulations are required before firm conclusions can be reached on the UV emission scenario because the VRI-band monitoring during the first caustic crossing and one of our two α indicators lead to a few good solutions with α ≈ 1.

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X-ray light curves of active galactic nuclei are phase incoherent

The Astrophysical Journal ◽

10.1086/172148 ◽

1993 ◽

Vol 402 ◽

pp. 432 ◽

Cited By ~ 10

Author(s):

Julian Krolik ◽

Chris Done ◽

Grzegorz Madejski

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Light Curves ◽

X Ray

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A physical model for the X-ray time lags of narrow-line Seyfert type 1 active galactic nuclei

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stu1026 ◽

2014 ◽

Vol 442 (3) ◽

pp. 2456-2473 ◽

Cited By ~ 23

Author(s):

Emma Gardner ◽

Chris Done

Keyword(s):

Active Galactic Nuclei ◽

Physical Model ◽

Galactic Nuclei ◽

Time Lags ◽

Narrow Line ◽

X Ray ◽

Seyfert Type

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Discovery of a relation between black hole mass and soft X-ray time lags in active galactic nuclei

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stt339 ◽

2013 ◽

Vol 431 (3) ◽

pp. 2441-2452 ◽

Cited By ~ 137

Author(s):

B. De Marco ◽

G. Ponti ◽

M. Cappi ◽

M. Dadina ◽

P. Uttley ◽

...

Keyword(s):

Black Hole ◽

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Time Lags ◽

Black Hole Mass ◽

X Ray

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A public relativistic transfer function model for X-ray reverberation mapping of accreting black holes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1720 ◽

2019 ◽

Vol 488 (1) ◽

pp. 324-347 ◽

Cited By ~ 14

Author(s):

Adam Ingram ◽

Guglielmo Mastroserio ◽

Thomas Dauser ◽

Pieter Hovenkamp ◽

Michiel van der Klis ◽

...

Keyword(s):

Black Holes ◽

Black Hole ◽

Active Galactic Nuclei ◽

Radial Profile ◽

Galactic Nuclei ◽

Seyfert Galaxy ◽

Geometric Constraints ◽

Time Lags ◽

X Ray ◽

X Ray Binaries

ABSTRACTWe present the publicly available model reltrans that calculates the light-crossing delays and energy shifts experienced by X-ray photons originally emitted close to the black hole when they reflect from the accretion disc and are scattered into our line of sight, accounting for all general relativistic effects. Our model is fast and flexible enough to be simultaneously fit to the observed energy-dependent cross-spectrum for a large range of Fourier frequencies, as well as to the time-averaged spectrum. This not only enables better geometric constraints than only modelling the relativistically broadened reflection features in the time-averaged spectrum, but additionally enables constraints on the mass of supermassive black holes in active galactic nuclei and stellar-mass black holes in X-ray binaries. We include a self-consistently calculated radial profile of the disc ionization parameter and properly account for the effect that the telescope response has on the predicted time lags. We find that a number of previous spectral analyses have measured artificially low source heights due to not accounting for the former effect and that timing analyses have been affected by the latter. In particular, the magnitude of the soft lags in active galactic nuclei may have been underestimated, and the magnitude of lags attributed to thermal reverberation in X-ray binaries may have been overestimated. We fit reltrans to the lag-energy spectrum of the Seyfert galaxy Mrk 335, resulting in a best-fitting black hole mass that is smaller than previous optical reverberation measurements (∼7 million compared with ∼14–26 million M⊙).

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Cosmic evolution of AGN with moderate-to-high radiative luminosity in the COSMOS field

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318000030 ◽

2017 ◽

Vol 12 (S333) ◽

pp. 195-198

Author(s):

L. Ceraj ◽

V. Smolčić ◽

I. Delvecchio ◽

J. Delhaize ◽

M. Novak

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Radio Continuum ◽

Continuum Emission ◽

Number Density ◽

X Ray ◽

Cosmic Evolution ◽

Luminosity Functions ◽

Multi Wavelength ◽

First Time

AbstractWe study the moderate-to-high radiative luminosity active galactic nuclei (HLAGN) within the VLA-COSMOS 3 GHz Large Project. The survey covers 2.6 square degrees centered on the COSMOS field with a 1σ sensitivity of 2.3 μJy/beam across the field. This provides the simultaneously largest and deepest radio continuum survey available to date with exquisite multi-wavelength coverage. The survey yields 10,830 radio sources with signal-to-noise ratios ≥5. A subsample of 1,604 HLAGN is analyzed here. These were selected via a combination of X-ray luminosity and mid-infrared colors. We derive luminosity functions for these AGN and constrain their cosmic evolution out to a redshift of z ∼ 6, for the first time decomposing the star formation and AGN contributions to the radio continuum emission in the AGN. We study the evolution of number density and luminosity density finding a peak at z ∼ 1.5 followed by a decrease out to a redshift z ∼ 6.

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Dust reverberation mapping of type 2 AGN NGC 2110 realized with X-ray and 3–5 μm IR monitoring

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1376 ◽

2020 ◽

Vol 495 (3) ◽

pp. 2921-2929

Author(s):

Hirofumi Noda ◽

Taiki Kawamuro ◽

Mitsuru Kokubo ◽

Takeo Minezaki

Keyword(s):

Time Lag ◽

Galactic Nuclei ◽

Light Curves ◽

Time Lags ◽

X Ray ◽

Reverberation Mapping ◽

Promising Tool ◽

Best Fitting

ABSTRACT The dust reverberation mapping is one of powerful methods to investigate the structure of the dusty tori in active galactic nuclei (AGNs), and it has been performed on more than a hundred type 1 AGNs. However, no clear results have been reported on type 2 AGNs because their strong optical/UV extinction completely hides their accretion disc emission. Here, we focus on an X-ray-bright type 2 AGN, NGC 2110, and utilize 2–20 keV X-ray variation monitored by MAXI to trace disc emission, instead of optical/UV variation. Comparing it with light curves in the WISE infrared (IR) W1 band ($\lambda =3.4~\mu$m) and W2 band ($\lambda =4.6~\mu$m) with cross-correlation analyses, we found candidates of the dust reverberation time lag at ∼60, ∼130, and ∼1250 d between the X-ray flux variation and those of the IR bands. By examining the best-fitting X-ray and IR light curves with the derived time lags, we found that the time lag of ∼130 d is most favoured. With this time lag, the relation between the time lag and luminosity of NGC 2110 is consistent with those in type 1 AGNs, suggesting that the dust reverberation in NGC 2110 mainly originates in hot dust in the torus innermost region, the same as in type 1 AGNs. As demonstrated by the present study, X-ray and IR simultaneous monitoring can be a promising tool to perform the dust reverberation mapping on type 2 AGNs.

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Emission of Accretion Disks

Symposium - International Astronomical Union ◽

10.1017/s0074180900175138 ◽

1994 ◽

Vol 159 ◽

pp. 261-270 ◽

Cited By ~ 1

Author(s):

B. Czerny

Keyword(s):

Active Galactic Nuclei ◽

Accretion Disks ◽

Ad Hoc ◽

Broad Band ◽

Galactic Nuclei ◽

Continuum Emission ◽

Massive Black Hole ◽

Disk Model ◽

Nuclear Activity ◽

X Ray

Accretion disks surrounding massive black hole is an attractive scenario of nuclear activity. A number of arguments support it although there is no unquestionable proof of the existence of accretion disks in active galactic nuclei. Meaningful comparison of the disk model prediction with the data can only be made if emission of accretion disks is calculated taking into account the existence of optically thin parts responsible for the emission of x-ray radiation. Nonlocal reprocessing phenomena have to be also included. Since we have no real understanding of the viscous processes operating in accretion disks some ad hoc parameterization of these processes has to be used and its applicability should be checked by broad band comparison of predictions for continuum emission and spectral features with available data.

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