scholarly journals Fluorescence in the Active Galactic Nuclei NGC 4151

2012 ◽  
Vol 8 (S295) ◽  
pp. 266-266
Author(s):  
Mattias Eriksson ◽  
Hans Veenhuizen
Keyword(s):  
Active Galactic Nuclei ◽  
Wavelength Region ◽  
Galactic Nuclei ◽  
Collisional Excitation ◽  
Ngc 4151 ◽  
Uv Emission

AbstractThe possibility of UV lines from Fe II formed in the BLR of NGC 4151 has been examined. As a result Fe II emission has been shown to play an important role for the topology of the 2000 to 3000 Å wavelength region of the NGC 4151 spectra. The Fe II UV emission originates from two processes, collisional excitation and PAR (photoexcitation by accidental resonance).

The nature of flux variations in the continua and broad-line regions of selected active galactic nuclei

2020 ◽  
Vol 496 (1) ◽  
pp. 784-800
Author(s):  
A Bewketu Belete ◽  
L J Goicoechea ◽  
B L Canto Martins ◽  
I C Leão ◽  
J R De Medeiros
Keyword(s):  
Active Galactic Nuclei ◽  
Moving Average ◽  
Sampling Rate ◽  
Galactic Nuclei ◽  
Small Sample ◽  
Light Curves ◽  
Ngc 4151 ◽  
The Given ◽  
Ngc 7469 ◽  
The Continuum

ABSTRACT We present a multifractal analysis of the long-term light curves of a small sample of type 1 active galactic nuclei: NGC 4151, Arp 102B, 3C 390.3, E1821+643 and NGC 7469. We aim to investigate how the degrees of multifractality of the continuum and Hβ line vary among the five different objects and to check whether the multifractal behaviours of the continuum and the Hβ line correlate with standard accretion parameters. The backward (θ  = 0) one-dimensional multifractal detrended moving average procedure was applied to light curves covering the full observation period and partial observation periods containing an equal number of epochs for each object. We detected multifractal signatures for the continua of NGC 4151, Arp 102B and 3C 390.3 and for the Hβ lines of NGC 4151 and 3C 390.3. However, we found nearly monofractal signatures for the continua of E1821+643 and NGC 7469, as well as for the Hβ lines of Arp 102B, E1821+643 and NGC 7469. In addition, we did not find any correlations between the degree of multifractality of the Hβ line and accretion parameters, while the degree of multifractality of the continuum seems to correlate with the Eddington ratio (i.e. the smaller the ratio is, the stronger the degree of multifractality). The given method is not robust, and these results should be taken with caution. Future analysis of the sampling rate and other properties of the light curves should help with better constraining and understanding these results.

scholarly journals Non-equilibrium chemistry and destruction of CO by X-ray flares

2019 ◽  
Vol 486 (1) ◽  
pp. 1094-1122 ◽  
Author(s):  
Jonathan Mackey ◽  
Stefanie Walch ◽  
Daniel Seifried ◽  
Simon C O Glover ◽  
Richard Wünsch ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Thermal Evolution ◽  
Galactic Nuclei ◽  
Galactic Centre ◽  
X Rays ◽  
X Ray ◽  
Uv Emission ◽  
Sgr A ◽  
X Ray Binaries ◽  
Fractal Cloud

ABSTRACT Sources of X-rays such as active galactic nuclei and X-ray binaries are often variable by orders of magnitude in luminosity over time-scales of years. During and after these flares the surrounding gas is out of chemical and thermal equilibrium. We introduce a new implementation of X-ray radiative transfer coupled to a time-dependent chemical network for use in 3D magnetohydrodynamical simulations. A static fractal molecular cloud is irradiated with X-rays of different intensity, and the chemical and thermal evolution of the cloud are studied. For a simulated $10^5\, \mathrm{M}_\odot$ fractal cloud, an X-ray flux <0.01 erg cm−2 s−1 allows the cloud to remain molecular, whereas most of the CO and H2 are destroyed for a flux of ≥1 erg cm−2 s−1. The effects of an X-ray flare, which suddenly increases the X-ray flux by 105×, are then studied. A cloud exposed to a bright flare has 99 per cent of its CO destroyed in 10–20 yr, whereas it takes >103 yr for 99 per cent of the H2 to be destroyed. CO is primarily destroyed by locally generated far-UV emission from collisions between non-thermal electrons and H2; He+ only becomes an important destruction agent when the CO abundance is already very small. After the flare is over, CO re-forms and approaches its equilibrium abundance after 103–105 yr. This implies that molecular clouds close to Sgr A⋆ in the Galactic Centre may still be out of chemical equilibrium, and we predict the existence of clouds near flaring X-ray sources in which CO has been mostly destroyed but H is fully molecular.

scholarly journals Infrared Line Shapes in Active Galactic Nuclei

1994 ◽  
Vol 159 ◽  
pp. 462-462
Author(s):  
Rodger I. Thompson
Keyword(s):  
Active Galactic Nuclei ◽  
Electron Density ◽  
Galactic Nuclei ◽  
Complete Spectrum ◽  
Line Shapes ◽  
Ngc 4151

This paper presents the complete spectrum of NGC 4151 from 0.87 to 2.5 μm as well as detail of the Paschen α profile in 3C273 at a resolution of about 5000. Analysis of the several observed Fe II lines yields a most probable electron density of 104 and a most likely temperature of 104. The Fe II to H ratio is 2+/− 1 × 10−6 which is 5–7% of the available iron if the Fe/H ratio is solar.

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

2020 ◽  
Vol 637 ◽  
pp. A89 ◽  
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.

scholarly journals X-Ray Properties of Galactic Nuclei

1980 ◽  
Vol 5 ◽  
pp. 623-630
Author(s):  
Daniel W. Weedman
Keyword(s):  
Emission Line ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxy ◽  
Seyfert Galaxies ◽  
Strong Emission ◽  
X Ray ◽  
Ngc 4151 ◽  
Survey Results ◽  
Emission Line Galaxies

Preparing this review was my just punishment for stating only two years ago - in another review (Weedman 1977) - that Seyfert galaxies are not strong X-ray sources. I said that because, as recently as three years ago, NGC 4151 was the only Seyfert galaxy known as an X-ray source. Now we have 36 Seyfert 1 galaxies, along with 12 other galaxies with strong emission-line nuclei, that are X-ray sources. And this is all without even having HEAO-2 data at our disposal yet. The study of active galactic nuclei with X-ray astronomy is progressing so rapidly that a reviewer feels almost hopeless. The best I can do is summarize what is known as of the summer of 1979 and give a simple overview of how X-ray and other properties relate.Some excellent reviews of the X-ray properties of Seyfert and other emission-line galaxies already exist. I especially recommend that by Andrew Wilson (1979). He provides very complete references as of a year ago, but X-ray astronomy is progressing so rapidly that he then had only somewhat more than half the active nuclei now in Tables 1 and 2. It was the group working with the Ariel V SSI that made the initial comprehensive X-ray studies of Seyfert galaxies (Ward et al. 1977, Elvis et al. 1978). The UHURU results for Seyfert galaxies followed soon after and are summarized by Tananbaum et al. (1978); the HEAO-A-2 survey results are now in press (Marshall et al. 1979) I have tried to incorporate these and other recent results in Tables 1 and 2.

scholarly journals Quasars as standard candles II

2019 ◽  
Vol 631 ◽  
pp. A120 ◽  
Author(s):  
F. Salvestrini ◽  
G. Risaliti ◽  
S. Bisogni ◽  
E. Lusso ◽  
C. Vignali
Keyword(s):  
Active Galactic Nuclei ◽  
Rest Frame ◽  
Galactic Nuclei ◽  
Observational Cosmology ◽  
X Ray ◽  
Uv Emission ◽  
Wide Range ◽  
Photon Index ◽  
Lower Redshift

A tight non-linear relation between the X-ray and the optical-ultraviolet (UV) emission has been observed in active galactic nuclei (AGN) over a wide range of redshift and several orders of magnitude in luminosity, suggesting the existence of an ubiquitous physical mechanism regulating the energy transfer between the accretion disc and the X-ray emitting corona. Recently, our group developed a method to use this relation in observational cosmology, turning quasars into standardizable candles. This work mainly seeks to investigate the potential evolution of this correction at high redshifts. We thus studied the LX − LUV relation for a sample of quasars in the redshift range 4 <  z <  7, adopting the selection criteria proposed in our previous work regarding their spectral properties. The resulting sample consists of 53 type 1 (unobscured) quasars, observed either with Chandra or XMM-Newton, for which we performed a full spectral analysis, determining the rest-frame 2 keV flux density, as well as more general X-ray properties such as the estimate of photon index, and the soft (0.5–2 keV) and hard (2–10 keV) unabsorbed luminosities. We find that the relation shows no evidence for evolution with redshift. The intrinsic dispersion of the LX–LUV for a sample free of systematics/contaminants is of the order of 0.22 dex, which is consistent with previous estimates from our group on quasars at lower redshift.

scholarly journals 1–3-Day Variations of the Broad Emission Lines of Seyfert Nuclei

1987 ◽  
Vol 121 ◽  
pp. 219-222
Author(s):  
Nikolay G. Bochkarev
Keyword(s):  
Active Galactic Nuclei ◽  
Angular Size ◽  
Galactic Nuclei ◽  
Photometric Data ◽  
Emission Lines ◽  
Line Profiles ◽  
Physical Processes ◽  
Ngc 4151 ◽  
Broad Emission ◽  
Broad Emission Line

One of the principal problems of investigation of AGNs is to understand the nature of the central objects and the physical processes which yield their gigantic luminosities. This requires us to consider the innermost parts of AGNs (3–30 gravitational radii, i.e. ≲ 1016 cm: angular size less than 1 milliarcsecond).1–3d variations of the relative shape of broad emission line profiles of active galactic nuclei (AGN) are perhaps the most informative probe of the innermost parts of AGNs (r = 1015–16 cm from the centre). Optimal objects for these observations are Sy 1.5 with strong variations of the non-thermal continuum (e.g. NGC 4151). The expected amplitude of the variations ranges from a few percent to 10–20%. The optimal spectral resolution is 0.5–5 Å. It is very desirable to complement spectral observations with photometric data. The results of the first set of such observations with the 6-meter telescope are reported.

scholarly journals Analyzing temporal variations of AGN emission line profiles in the context of (dusty) cloud structure formation in the broad line region

2019 ◽  
Vol 621 ◽  
pp. A46 ◽  
Author(s):  
J. Esser ◽  
J.-U. Pott ◽  
H. Landt ◽  
W. D. Vacca
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Galactic Nuclei ◽  
Temporal Variations ◽  
Cloud Formation ◽  
Broad Line ◽  
Ngc 4151 ◽  
Broad Line Region ◽  
The Past ◽  
Line Region

The formation processes and the exact appearance of the dust torus and broad line region (BLR) of active galactic nuclei (AGN) are under debate. Theoretical studies show a possible connection between the dust torus and BLR through a common origin in the accretion disk. However observationally the dust torus and BLR are typically studied separately. NGC 4151 is possibly one of the best suited Seyfert 1 galaxies for simultaneous examinations because of its high number of both photometric and spectroscopic observations in the past. Here we compare changes of the dust radius to shape variations of broad emission lines (BEL). While the radius of the dust torus decreased by almost a factor of two from 2004 to 2006 shape variations can be seen in the red wing of BELs of NGC 4151. These simultaneous changes are discussed in a dust and BEL formation scheme. We also use the BEL shape variations to assess possible cloud distributions, especially in azimuthal direction, which could be responsible for the observed variations. Our findings can best be explained in the framework of a dust inflated accretion disk. The changes in the BELs suggest that this dusty cloud formation does not happen continuously, and over the whole accretion disk, but on the contrary in spatially confined areas over rather short amount of times. We derive limits to the azimuthal extension of the observed localized BEL flux enhancement event.

scholarly journals Broad UV Emission Lines in Type-1 Active Galactic Nuclei: A Note on Spectral Diagnostics and the Excitation Mechanism

Atoms ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 94
Author(s):  
Paola Marziani ◽  
Ascension del Olmo ◽  
Jaime Perea ◽  
Mauro D’Onofrio ◽  
Swayamtrupta Panda
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
General Purpose ◽  
Emission Lines ◽  
Impact Excitation ◽  
Ionization Degree ◽  
Uv Emission ◽  
Spectral Diagnostics ◽  
Ionization Parameter

This paper reviews several basic emission properties of the UV emission lines observed in the spectra of quasars and type-1 active galactic nuclei, mainly as a function of the ionization parameter, metallicity, and density of the emitting gas. The analysis exploits a general-purpose 4D array of the photoionization simulations computed using the code CLOUDY, covering ionization parameter in the range 10−4.5–10+1.0, hydrogen density nH∼107–1014 cm−3, metallicity Z between 0.01 and 100 Z⊙, and column density in the range 1021–1023 cm−2. The focus is on the most prominent UV emission lines observed in quasar spectra, namely Nvλ1240, Siivλ1397, Oiv]λ1402, Civλ1549, Heiiλ1640, Aliiiλ1860, Siiii]λ1892, and Ciii]λ1909, and on the physical conditions under which electron-ion impact excitation is predicted to be the dominant line producer. Photoionization simulations help constrain the physical interpretation and the domain of applicability of spectral diagnostics derived from measurements of emission line ratios, reputed to be important for estimating the ionization degree, density, and metallicity of the broad line emitting gas, as well as the relative intensity ratios of the doublet or multiplet components relevant for empirical spectral modeling.

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