scholarly journals Multifrequency Variability of AGN's: Continuum Variations from the Near IR to the X-rays

1994 ◽  
Vol 159 ◽  
pp. 131-143
Author(s):  
J. Clavel
Keyword(s):  
Active Galactic Nuclei ◽  
Temporal Evolution ◽  
Line Emission ◽  
Galactic Nuclei ◽  
The Other ◽  
X Rays ◽  
Optical Telescope ◽  
Emission Process ◽  
Near Ir ◽  
The Continuum

Because they emit copiously over more than 10 decades in frequency, Active Galactic Nuclei (AGN) cannot be understood without the help of multiwavelength observations. On the other hand, variability monitoring has also proven to be invaluable in understanding the continuum and line emission process as well as the geometry of the innermost regions in these objects. Indeed, at the heart of AGN's lies an object which is so compact that the only way to probe its structure is the study of the temporal evolution of its spectrum. The equivalent resolution which can be achieved in this way is of the order of 10 microarcsecs, far beyond the capability of any UV or optical telescope.

scholarly journals Line Emission from Accretion Disks in Active Galactic Nuclei

1989 ◽  
Vol 134 ◽  
pp. 255-256
Author(s):  
S. Collin-Souffrin ◽  
A.M. Dumont
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Disks ◽  
Line Emission ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
X Rays ◽  
X Ray ◽  
Outer Disk ◽  
Inverse Compton ◽  
Inner Region

If accretion disks are present in AGN and extend to large radii they should contribute substantially to the Broad Line emission. The outer regions of the disk are indeed illuminated by a small amount of ionizing radiation. X-rays are emitted by the central inner region near the black hole, and they are either received directly by the outer disk, owing to its “flaring” shape (Cunningham, 1976), or partly reflected towards the disk by a hot Compton thin medium (Begelmann and McKee, 1983). X-ray photons are also produced through the Inverse Compton mechanism in compact radio sources located above the disk(“jet model”).

scholarly journals A deep X-ray view of the bare AGN Ark 120

2018 ◽  
Vol 609 ◽  
pp. A42 ◽  
Author(s):  
D. Porquet ◽  
J. N. Reeves ◽  
G. Matt ◽  
A. Marinucci ◽  
E. Nardini ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Line Of Sight ◽  
Constant Density ◽  
High Flux ◽  
X Rays ◽  
X Ray ◽  
Intrinsic Absorption ◽  
The Continuum

Context. The physical characteristics of the material closest to supermassive black holes (SMBHs) are primarily studied through X-ray observations. However, the origins of the main X-ray components such as the soft X-ray excess, the Fe Kα line complex, and the hard X-ray excess are still hotly debated. This is particularly problematic for active galactic nuclei (AGN) showing a significant intrinsic absorption, either warm or neutral, which can severely distort the observed continuum. Therefore, AGN with no (or very weak) intrinsic absorption along the line of sight, so-called “bare AGN”, are the best targets to directly probe matter very close to the SMBH. Aims. We perform an X-ray spectral analysis of the brightest and cleanest bare AGN known so far, Ark 120, in order to determine the process(es) at work in the vicinity of the SMBH. Methods. We present spectral analyses of data from an extensive campaign observing Ark 120 in X-rays with XMM-Newton (4 × 120 ks, 2014 March 18–24), and NuSTAR (65.5 ks, 2014 March 22). Results. During this very deep X-ray campaign, the source was caught in a high-flux state similar to the earlier 2003 XMM-Newton observation, and about twice as bright as the lower-flux observation in 2013. The spectral analysis confirms the “softer when brighter” behavior of Ark 120. The four XMM-Newton/pn spectra are characterized by the presence of a prominent soft X-ray excess and a significant Fe Kα complex. The continuum is very similar above about 3 keV, while significant variability is present for the soft X-ray excess. We find that relativistic reflection from a constant-density, flat accretion disk cannot simultaneously produce the soft excess, broad Fe Kα complex, and hard X-ray excess. Instead, Comptonization reproduces the broadband (0.3–79 keV) continuum well, together with a contribution from a mildly relativistic disk reflection spectrum. Conclusions. During this 2014 observational campaign, the soft X-ray spectrum of Ark 120 below ~0.5 keV was found to be dominated by Comptonization of seed photons from the disk by a warm (kTe ~ 0.5 keV), optically-thick corona (τ ~ 9). Above this energy, the X-ray spectrum becomes dominated by Comptonization from electrons in a hot optically thin corona, while the broad Fe Kα line and the mild Compton hump result from reflection off the disk at several tens of gravitational radii.

scholarly journals Water maser and radio continuum emission towards IRAS 23139+5939

2007 ◽  
Vol 3 (S242) ◽  
pp. 180-181
Author(s):  
M. A. Trinidad ◽  
S. Curiel ◽  
J. M. Torrelles ◽  
L. F. Rodríguez ◽  
V. Migenes ◽  
...  
Keyword(s):  
Flux Density ◽  
Line Emission ◽  
The Other ◽  
Radio Continuum ◽  
High Mass ◽  
Continuum Emission ◽  
Maser Line ◽  
Water Masers ◽  
Water Maser ◽  
The Continuum

AbstractWe present simultaneous observations of continuum (3.5 and 1.3cm) and water maser line emission (1.3cm) carried out with the VLA-A toward the high-mass object IRAS 23139+5939. We detected two radio continuum sources at 3.5cm separated by 0”5 (~2400 AU), I23139 and I23139S. Based on the observed continuum flux density and the spectral index, we suggest that I23139 is a thermal radio jet associated with a high-mass YSO. On the other hand, based on the spatio-kinematical distribution of the water masers, together with the continuum emission information, we speculate that I23139S is also a jet source powering some of the masers detected in the region.

scholarly journals Optical Flares from the Tidal Disruption of Stars by Massive Black Holes

2009 ◽  
Vol 5 (S267) ◽  
pp. 337-337 ◽  
Author(s):  
Linda E. Strubbe ◽  
Eliot Quataert
Keyword(s):  
Galactic Nuclei ◽  
Stellar Dynamics ◽  
Theoretical Models ◽  
X Rays ◽  
Tidal Disruption ◽  
Massive Black Hole ◽  
Detection Rates ◽  
Massive Black Holes ◽  
Near Ir ◽  
Nuclear Regions

A star that wanders too close to a massive black hole (BH) is shredded by the BH's tidal gravity. Stellar gas falls back to the BH, releasing a flare of energy. In anticipation of upcoming transient surveys, we predict the light curves and spectra of tidal flares as a function of time, highlighting the unique signatures of tidal flares in the optical and near-IR. Some of the gas initially bound to the BH is likely blown away when the fallback rate is super-Eddington at early times. This outflow produces an optical luminosity comparable to that of a supernova (Figure 1, left panel); such events have durations of ~ 10 days and may have been missed in supernova searches that exclude the nuclear regions of galaxies. When the fallback rate subsides below Eddington, the gas accretes onto the BH via a thin disk whose emission peaks in the UV to soft X-rays. Some of this emission is reprocessed by the unbound stellar debris, producing a spectrum of very broad emission lines, with no corresponding narrow forbidden lines (center panel). These lines are strongest for BHs with MBH ~ 105–106M⊙ and thus optical surveys are particularly sensitive to the lowest mass BHs in galactic nuclei. Calibrating our models to ROSAT and GALEX observations, we predict detection rates for Pan-STARRS, Palomar Transit Factory, and LSST (right panel) and highlight observational challenges in the optical. Pan-STARRS should detect at least several events per year — many more if current theoretical models of super-Eddington outflows are correct. These surveys will significantly improve our knowledge of stellar dynamics in galactic nuclei, the physics of super-Eddington accretion, the demography of intermediate mass BHs, and the role of tidal disruption in the growth of massive BHs.

scholarly journals Co-existence of two plasma phases in solar and AGN coronas

1998 ◽  
pp. 43-53
Author(s):  
A. Kubicela ◽  
J. Arsenijevic ◽  
L.C. Popovic ◽  
N. Trajkovic ◽  
E. Bon
Keyword(s):  
Solar Corona ◽  
Active Galactic Nuclei ◽  
Research Work ◽  
Neutral Hydrogen ◽  
Galactic Nuclei ◽  
Theoretical Explanation ◽  
The Other ◽  
Solar Photosphere ◽  
Hydrogen Lines ◽  
Hot Corona

Here we have juxtaposed two distant cosmic locations of the Sun and AGN where neutral hydrogen appears in a close connection with hot coronas. Besides the solar photosphere, chromosphere and prominences where the presence of neutral hydrogen is well established, its emission quite high in hot solar corona is still puzzling. Some of earlier observations where H? emission in solar corona was detected in eclipse and in daily coronagraphic observations are reviewed. A proper theoretical explanation of this cold chromospheric-type emission in the hot corona does not exist yet. On the other side, a similar emission of hydrogen lines is present in Active Galactic Nuclei (AGNs). Much research work is currently being done in this field. We outline some of the concepts of the AGN structure prevailing in the astrophysics today.

scholarly journals The Southern 2MASS Active Galactic Nuclei Survey: Spectroscopic Follow-up with Six Degree Field

2010 ◽  
Vol 27 (3) ◽  
pp. 302-320 ◽  
Author(s):  
Frank J. Masci ◽  
Roc M. Cutri ◽  
Paul J. Francis ◽  
Brant O. Nelson ◽  
John P. Huchra ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Far Infrared ◽  
Type I ◽  
Galactic Latitude ◽  
Stellar Objects ◽  
Identification Rate ◽  
Near Ir ◽  
The Uk ◽  
Probable Type

AbstractThe Two Micron All-Sky Survey (2MASS) has provided a uniform photometric catalog to search for previously unknown red active galactic nuclei (AGN) and Quasi-Stellar Objects (QSOs).We have extended the search to the southern equatorial sky by obtaining spectra for 1182 AGN candidates using the six degree field (6dF) multifibre spectrograph on the UK Schmidt Telescope. These were scheduled as auxiliary targets for the 6dF Galaxy Redshift Survey. The candidates were selected using a single color cut of J – Ks > 2 to Ks ≲ 15.5 and a galactic latitude of lbl > 30°. 432 spectra were of sufficient quality to enable a reliable classification. 116 sources (∼27%) were securely classified as type I AGN, 20 as probable type I AGN, and 57 as probable type II AGN. Most of them span the redshift range 0.05 < z < 0.5 and only 8 (∼6%) were previously identified as AGN or QSOs. Our selection leads to a significantly higher AGN identification rate amongst local galaxies (>20%) than in any previous (mostly blue-selected) galaxy survey. A small fraction of the type I AGN could have their optical colors reddened by optically thin dust with AV < 2 mag relative to optically selected QSOs. A handful show evidence of excess far-infrared (IR) emission. The equivalent width (EW) and color distributions of the type I and II AGN are consistent with AGN unified models. In particular, the EW of the [Oiii] emission line weakly correlates with optical–near-IR color in each class of AGN, suggesting anisotropic obscuration of the AGN continuum. Overall, the optical properties of the 2MASS red AGN are not dramatically different from those of optically-selected QSOs. Our near-IR selection appears to detect the most near-IR luminous QSOs in the local universe to z≃0.6 and provides incentive to extend the search to deeper near-IR surveys.

scholarly journals Structure and Emission Line Spectrum of an X-ray Heated Accretion Disk in AGN

1994 ◽  
Vol 159 ◽  
pp. 484-484
Author(s):  
Yuan-Kuen Ko ◽  
Timothy R. Kallman
Keyword(s):  
Emission Line ◽  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Line Emission ◽  
Galactic Nuclei ◽  
X Ray ◽  
Disk Size ◽  
Emission Line Spectrum ◽  
Self Gravity ◽  
A Site

We investigate the structure of an X-ray heated accretion disk in active galactic nuclei. It is found that X-ray heating can prevent the disk to be disrupted by its self-gravity under sufficient X-ray heating. The disk size can be two orders of magnitute larger than that limited by self-gravity of the disk without X-ray heating. An accretion disk corona will be formed by X-ray heating and can be a site for line emission. We present such emission line spectra which range from optical to hard X-ray energies and compare with the observational data.

scholarly journals Discovery of diffuse optical emission lines from the inner Galaxy: Evidence for LI(N)ER-like gas

2020 ◽  
Vol 6 (27) ◽  
pp. eaay9711 ◽  
Author(s):  
D. Krishnarao ◽  
R. A. Benjamin ◽  
L. M. Haffner
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Center ◽  
Line Emission ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Hydrogen Gas ◽  
Emission Lines ◽  
Neutral Gas ◽  
Optical Line ◽  
Tilted Disk

Optical emission lines are used to categorize galaxies into three groups according to their dominant central radiation source: active galactic nuclei, star formation, or low-ionization (nuclear) emission regions [LI(N)ERs] that may trace ionizing radiation from older stellar populations. Using the Wisconsin H-Alpha Mapper, we detect optical line emission in low-extinction windows within eight degrees of Galactic Center. The emission is associated with the 1.5-kiloparsec-radius “Tilted Disk” of neutral gas. We modify a model of this disk and find that the hydrogen gas observed is at least 48% ionized. The ratio [NII] λ6584 angstroms/Hα λ6563 angstroms increases from 0.3 to 2.5 with Galactocentric radius; [OIII] λ5007 angstroms and Hβ λ4861 angstroms are also sometimes detected. The line ratios for most Tilted Disk sightlines are characteristic of LI(N)ER galaxies.

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.

Sign in / Sign up

Export Citation Format

Share Document