scholarly journals Flux States of Active Galactic Nuclei

Galaxies ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 57
Author(s):  
Daniela Dorner ◽  
Axel Arbet-Engels ◽  
Dominik Baack ◽  
Matteo Balbo ◽  
Adrian Biland ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Time Scales ◽  
Duty Cycle ◽  
Main Part ◽  
Flux Distribution ◽  
Galactic Nuclei ◽  
Quiescent State ◽  
Wide Range ◽  
Multi Wavelength

Blazars are known to show variability on time scales from minutes to years covering a wide range of flux states. Studying the flux distribution of a source allows for various insights. The shape of the flux distribution can provide information on the nature of the underlying variability processes. The level of a possible quiescent state can be derived from the main part of the distribution that can be described by a Gaussian distribution. Dividing the flux states into quiescent and active, the duty cycle of a source can be calculated. Finally, this allows alerting the multi-wavelength and multi-messenger community in case a source is in an active state. To get consistent and conclusive results from flux distributions, unbiased long-term observations are crucial. Only like this is a complete picture of the variability and flux states, e.g., an all-time quiescent state, possible. In seven years of monitoring of bright TeV blazars, the first G-APD Cherenkov telescope (FACT) has collected a total of more than 11,700 hours of physics data with 1500 hours to 3000 hours per source for Mrk 421, Mrk 501, 1ES 1959+650, and 1ES 2344+51.

The Extremes of AGN Variability

2016 ◽  
Vol 12 (S324) ◽  
pp. 168-171 ◽  
Author(s):  
S. Komossa ◽  
D. Grupe ◽  
N. Schartel ◽  
L. Gallo ◽  
J. L. Gomez ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
X Ray ◽  
Accretion Flow ◽  
Multi Wavelength ◽  
Long Term Monitoring ◽  
Term Monitoring ◽  
Spectral States ◽  
Ongoing Monitoring

AbstractWe present results from our ongoing monitoring programs aimed at identifying and understanding Active Galactic Nuclei (AGN) in extreme flux and spectral states. Observations of AGN in extreme states can reveal the nature of the inner accretion flow, the physics of matter under strong gravity, and they provide insight on the properties of ionized absorbers and outflows launched near supermassive black holes (SMBHs). We present new results from our long-term monitoring of IC 3599, WPVS007, and Mrk 335, multi-wavelength follow-ups of the newly identified changing-look AGN HE 1136–2304, and UV–X-ray follow-ups of the binary SMBH candidate OJ 287 after its 2015 optical maximum, now in a new optical-X-ray–high-state.

scholarly journals The Optical Spectral Slope Variability for 17 Palomar-Green QSOs

2006 ◽  
Vol 2 (S235) ◽  
pp. 78-78
Author(s):  
X. Pu ◽  
W. Bian ◽  
K. Huang
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Spectral Variability ◽  
Strong Emission ◽  
Spectroscopic Monitoring ◽  
Central Engine ◽  
Multi Wavelength ◽  
Long Time ◽  
Photometric Monitoring

Variability phenomenon in active galactic nuclei (AGNs) provides a powerful constrain on their central engine. For a long time the long-term multi-wavelength photometric monitoring plays an important role in obtaining the optical variability of QSOs. However, it just monitors the flux variability in a few points in the wavelength which usually consists of many components including continuum and strong emission line (although the photometric data are accurate). So it is necessary to study the optical spectral variability using spectroscopic monitoring data.

scholarly journals X-ray variability in LINERs

2013 ◽  
Vol 9 (S304) ◽  
pp. 399-402
Author(s):  
Josefa Masegosa ◽  
Lorena Hernández-García ◽  
Isabel Márquez ◽  
Omaira González-Martín
Keyword(s):  
Active Galactic Nuclei ◽  
Time Scales ◽  
Galactic Nuclei ◽  
Spectral Variability ◽  
X Ray ◽  
Line Region ◽  
Variability Pattern ◽  
Long Time ◽  
Public Archives

AbstractOne of the most important features in active galactic nuclei (AGN) is the variability of their emission. Variability has been discovered at X-ray, UV, and radio frequencies on time scales from hours to years. Among the AGN family and according to theoretical studies, Low-Ionization Nuclear Emission Line Region (LINER) nuclei would be variable objects on long time scales. Our purpose is to investigate spectral X-ray variability in LINERs and to understand the nature of these kinds of objects, as well as their accretion mechanism. Chandra and XMM–Newton public archives were used to compile X-ray spectra of LINER nuclei at different epochs with time scales of years. To search for variability we fit all the spectra from the same object with a set of models, in order to identify the parameters responsible for the variability pattern. We found that long term spectral variability is very common, with variations mostly related to hard energies (2-10 keV). These variations are due to changes in the soft excess, and/or changes in the absorber, and/or intrinsic variations of the source.

scholarly journals Variability in Active Galactic Nuclei

1993 ◽  
Vol 134 ◽  
pp. 245-547
Author(s):  
M. Matsuoka
Keyword(s):  
Active Galactic Nuclei ◽  
Time Scales ◽  
Galactic Nuclei ◽  
Wide Band ◽  
Seyfert Galaxies ◽  
Time Variability ◽  
X Ray ◽  
Central Engine ◽  
Nearby Region ◽  
Wide Range

AbstractAGN (Active Galactic Nuclei) have their profound time variability over a wide range of time scales. Although many results of AGN variability have been provided from wide band wavelength observations, I would like to concentrate the recent problems concerning a nearby region of their central engine based on the X-ray observations which are most efficient to investigate this region. In this paper we will investigate mainly the result of Seyfert galaxies which would be generalized to other AGN.

scholarly journals Polarimetric Properties of Blazars Caught by the WEBT

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 42
Author(s):  
Claudia M. Raiteri ◽  
Massimo Villata
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Plasma Jets ◽  
Line Of Sight ◽  
Optical Behaviour ◽  
Relativistic Jets ◽  
Comprehensive Picture ◽  
Multi Wavelength ◽  
Extreme Variability ◽  
Continuous Range

Active galactic nuclei come in many varieties. A minority of them are radio-loud, and exhibit two opposite prominent plasma jets extending from the proximity of the supermassive black hole up to megaparsec distances. When one of the relativistic jets is oriented closely to the line of sight, its emission is Doppler beamed and these objects show extreme variability properties at all wavelengths. These are called “blazars”. The unpredictable blazar variability, occurring on a continuous range of time-scales, from minutes to years, is most effectively investigated in a multi-wavelength context. Ground-based and space observations together contribute to give us a comprehensive picture of the blazar emission properties from the radio to the γ-ray band. Moreover, in recent years, a lot of effort has been devoted to the observation and analysis of the blazar polarimetric radio and optical behaviour, showing strong variability of both the polarisation degree and angle. The Whole Earth Blazar Telescope (WEBT) Collaboration, involving many tens of astronomers all around the globe, has been monitoring several blazars since 1997. The results of the corresponding data analysis have contributed to the understanding of the blazar phenomenon, particularly stressing the viability of a geometrical interpretation of the blazar variability. We review here the most significant polarimetric results achieved in the WEBT studies.

SDSS J154751.94+025550 with double-peaked broad H β but single-peaked broad H α: a candidate for central binary black hole system?

2021 ◽  
Vol 507 (4) ◽  
pp. 5205-5213
Author(s):  
XueGuang Zhang
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Emission Lines ◽  
Broad Line ◽  
Line Profiles ◽  
Physical Conditions ◽  
Binary Black Hole ◽  
Sinusoidal Function

ABSTRACT In this manuscript, an interesting blue active galactic nuclei (AGNs) SDSS J154751.94+025550 (=SDSS J1547) is reported with very different line profiles of broad Balmer emission lines: double-peaked broad H β but single-peaked broad H α. SDSS J1547 is the first AGN with detailed discussions on very different line profiles of the broad Balmer emission lines, besides the simply mentioned different broad lines in the candidate for a binary black hole (BBH) system in SDSS J0159+0105. The very different line profiles of the broad Balmer emission lines can be well explained by different physical conditions to two central BLRs in a central BBH system in SDSS J1547. Furthermore, the long-term light curve from CSS can be well described by a sinusoidal function with a periodicity about 2159 d, providing further evidence to support the expected central BBH system in SDSS J1547. Therefore, it is interesting to treat different line profiles of broad Balmer emission lines as intrinsic indicators of central BBH systems in broad line AGN. Under assumptions of BBH systems, 0.125 per cent of broad-line AGN can be expected to have very different line profiles of broad Balmer emission lines. Future study on more broad line AGN with very different line profiles of broad Balmer emission lines could provide further clues on the different line profiles of broad Balmer emission lines as indicator of BBH systems.

scholarly journals X-ray variability time scales in active galactic nuclei

2009 ◽  
Vol 504 (1) ◽  
pp. 61-66 ◽  
Author(s):  
W. Ishibashi ◽  
T. J.-L. Courvoisier
Keyword(s):  
Active Galactic Nuclei ◽  
Time Scales ◽  
Galactic Nuclei ◽  
X Ray

scholarly journals AGN polarization modeling with Stokes

2006 ◽  
Vol 2 (S238) ◽  
pp. 375-376 ◽  
Author(s):  
René W. Goosmann ◽  
C. Martin Gaskell ◽  
Masatoshi Shoji
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Dust Grains ◽  
Free Electrons ◽  
Wide Range ◽  
Polarization Spectra

AbstractWe introduce a new, publicly available Monte Carlo radiative transfer code, Stokes, which has been developed to model polarization induced by scattering of free electrons and dust grains. It can be used in a wide range of astrophysical applications. Here, we apply it to model the polarization produced by the equatorial obscuring and scattering tori assumed to exist in active galactic nuclei (AGNs). We present optical/UV modeling of dusty tori with a curved inner shape and for two different dust types. The polarization spectra enable us to clearly distinguish between the two dust compositions. The Stokes code and its documentation can be freely downloaded from http://www.stokes-program.info/.

scholarly journals Proper motion in lensed radio jets at redshift 3: A possible dual super-massive black hole system in the early Universe

2019 ◽  
Vol 630 ◽  
pp. A108 ◽  
Author(s):  
C. Spingola ◽  
J. P. McKean ◽  
D. Massari ◽  
L. V. E. Koopmans
Keyword(s):  
Active Galactic Nuclei ◽  
Early Universe ◽  
Gravitational Lensing ◽  
Proper Motion ◽  
Galactic Nuclei ◽  
Massive Black Hole ◽  
Radio Jets ◽  
Long Baseline ◽  
Multi Wavelength ◽  
Low Probability

In this paper, we exploit the gravitational lensing effect to detect proper motion in the highly magnified gravitationally lensed source MG B2016+112. We find positional shifts up to 6 mas in the lensed images by comparing two Very Long Baseline Interferometric (VLBI) radio observations at 1.7 GHz that are separated by 14.359 years, and provide an astrometric accuracy of the order of tens of μas. From lens modelling, we exclude a shift in the lensing galaxy as the cause of the positional change of the lensed images, and we assign it to the background source. The source consists of four sub-components separated by ∼175 pc, with proper motion of the order of tens μas yr−1 for the two components at highest magnification (μ ∼ 350) and of the order of a few mas yr−1 for the two components at lower magnification (μ ∼ 2). We propose single active galactic nuclei (AGN) and dual AGN scenarios to explain the source plane. Although, the latter interpretation is supported by the archival multi-wavelength properties of the object. In this case, MG B2016+112 would represent the highest redshift dual radio-loud AGN system discovered thus far, and would support the merger interpretation for such systems. Also, given the low probability (∼10−5) of detecting a dual AGN system that is also gravitationally lensed, if confirmed, this would suggest that such dual AGN systems must be more abundant in the early Universe than currently thought.

scholarly journals Swift/XRT, Chandra, and XMM–Newton observations of IGR J17091–3624 as it returns into quiescence

2020 ◽  
Vol 497 (1) ◽  
pp. 1115-1126
Author(s):  
M Pereyra ◽  
D Altamirano ◽  
J M C Court ◽  
N Degenaar ◽  
R Wijnands ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Time Scales ◽  
Strong Evidence ◽  
Spectral Properties ◽  
X Ray ◽  
Term Evolution ◽  
Wide Range ◽  
Low Mass

ABSTRACT IGR J17091–3624 is a low-mass X-ray binary (LMXB), which received wide attention from the community thanks to its similarities with the bright black hole system GRS 1915+105. Both systems exhibit a wide range of highly structured X-ray variability during outburst, with time-scales from few seconds to tens of minutes, which make them unique in the study of mass accretion in LMXBs. In this work, we present a general overview into the long-term evolution of IGR J17091–3624, using Swift/XRT observations from the onset of the 2011–2013 outburst in 2011 February till the end of the last bright outburst in 2016 November. We found four re-flares during the decay of the 2011 outburst, but no similar re-flares appear to be present in the latter one. We studied, in detail, the period with the lowest flux observed in the last 10 yr, just at the tail end of the 2011–2013 outburst, using Chandra and XMM-Newton observations. We observed changes in flux as high as a factor of 10 during this period of relative quiescence, without strong evidence of softening in the spectra. This result suggests that the source has not been observed at its true quiescence so far. By comparing the spectral properties at low luminosities of IGR J17091–3624 and those observed for a well-studied population of LMXBs, we concluded that IGR J17091–3624 is most likely to host a black hole as a compact companion rather than a neutron star.

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