On the origin of power-law X-ray spectra of active galactic nuclei

1984 ◽  
Vol 287 ◽  
pp. 534 ◽  
Author(s):  
I. Schlosman ◽  
J. Shaham ◽  
G. Shaviv
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
X Ray

scholarly journals X-ray variability of 104 active galactic nuclei

2012 ◽  
Vol 8 (S290) ◽  
pp. 37-40
Author(s):  
O. González-Martín ◽  
S. Vaughan
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Power Law Model ◽  
Black Hole Mass ◽  
Periodic Oscillations ◽  
Fundamental Plane ◽  
X Ray ◽  
Single Power

AbstractWe have performed a uniform analysis of the power spectrum densities (PSDs) of 104 nearby (z<0.4) active galactic nuclei (AGN) using 209 XMM-Newton/pn observations, including several AGN classes. These PSDs span ≃ 3 decades in temporal frequencies, ranging from minutes to days. We have fitted each PSD to two models: (1) a single power-law model and (2) a bending power-law model. A fraction of 72% show significant variability. The PSD of the majority of the variable AGN was well described by a simple power-law with a mean index of α = 2.01±0.01. In 15 sources we found that the bending power law model was preferred with a mean slope of α = 3.08±0.04 and a mean bend frequency of 〈νb〉 ≃ 2 × 10−4 Hz. Only KUG 1031+398 (RE J1034+396) shows evidence for quasi-periodic oscillations. The ‘fundamental plane’ relating variability timescale, black hole mass, and luminosity is demonstrated using the new X-ray timing results presented here together with a compilation of the previously detected timescales from the literature.

scholarly journals Examining the physical conditions of a warm corona in active galactic nuclei accretion discs

2019 ◽  
Vol 491 (3) ◽  
pp. 3553-3561 ◽  
Author(s):  
D R Ballantyne
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Accretion Discs ◽  
Internal Heating ◽  
One Dimensional ◽  
X Ray ◽  
Physical Conditions ◽  
Gas Layer ◽  
Hot Corona

ABSTRACT A warm corona at the surface of an accretion disc has been proposed as a potential location for producing the soft excess commonly observed in the X-ray spectra of active galactic nuclei (AGNs). In order to fit the observed data, the gas must be at temperatures of ∼1 keV and have an optical depth of τT ≈ 10–20. We present one-dimensional calculations of the physical conditions and emitted spectra of a τT = 10 or 20 gas layer subject to illumination from an X-ray power law (from above), a blackbody (from below), and a variable amount of internal heating. The models show that a warm corona with kT ∼ 1 keV can develop, producing a strong Comptonized soft excess, but only if the internal heating flux is within a relatively narrow range. Similarly, if the gas density of the layer is too large then efficient cooling will stop a warm corona from forming. The radiation from the hard X-ray power law is crucial in producing a warm corona, indicating that a warm and hot corona may coexist in AGN accretion discs, and their combined effect leads to the observed soft excess. Intense heating of a warm corona leads to steep X-ray spectra with ionized Fe K α lines, similar to those seen in some narrow-line Seyfert 1 galaxies.

scholarly journals EUV and Soft X-ray Evidence for Partially Ionized Gas in Active Galactic Nuclei

1996 ◽  
Vol 152 ◽  
pp. 45-49
Author(s):  
J.P.D. Mittaz ◽  
R. Lieu ◽  
S. Bowyer ◽  
C.-Y. Hwang ◽  
J. Lewis
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Ionized Gas ◽  
X Ray ◽  
Partially Ionized ◽  
Best Fit

We present a synoptic study of active galactic nuclei (AGN) detected by EUVE. We also present complementary ROSAT PSPC spectra for these sources and for other AGN in directions of low galactic absorption. It is found that the best-fit power-law photon indices of the X-ray spectra at 0.1–2.4 keV are anti-correlated with their galactic hydrogen columns. The indices for the 0.9–2.4 keV range do not show such a correlation, and are considerably smaller (i.e. flatter). We discuss a number of possible interpretations of this correlation but only one of these, the presence of a partially ionized absorbing gas in the AGN, explains the observations satisfactorily. The ubiquity of this effect suggests that this component be may very common in AGN.

scholarly journals X-ray power law spectra in active galactic nuclei

2010 ◽  
Vol 512 ◽  
pp. A58 ◽  
Author(s):  
W. Ishibashi ◽  
T. J.-L. Courvoisier
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
X Ray

scholarly journals 15-GHz radio emission from nearby low-luminosity active galactic nuclei

2018 ◽  
Vol 616 ◽  
pp. A152 ◽  
Author(s):  
Payaswini Saikia ◽  
Elmar Körding ◽  
Deanne L. Coppejans ◽  
Heino Falcke ◽  
David Williams ◽  
...  
Keyword(s):  
Black Hole ◽  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Power Law ◽  
Critical Mass ◽  
Galactic Nuclei ◽  
Radio Luminosity ◽  
Solar Mass ◽  
Fundamental Plane ◽  
X Ray

We present a sub-arcsec resolution radio imaging survey of a sample of 76 low-luminosity active galactic nuclei (LLAGN) that were previously not detected with the Very Large Array at 15 GHz. Compact, parsec-scale radio emission has been detected above a flux density of 40 μ Jy in 60% (45 of 76) of the LLAGN sample. We detect 20 out of 31 (64%) low-ionization nuclear emission-line region (LINER) nuclei, ten out of 14 (71%) low-luminosity Seyfert galaxies, and 15 out of 31 (48%) transition objects. We use this sample to explore correlations between different emission lines and the radio luminosity. We also populate the X-ray and the optical fundamental plane of black hole activity and further refine its parameters. We obtain a fundamental plane relation of log LR = 0.48 (±0.04) log LX + 0.79 (±0.03) log M and an optical fundamental plane relation of log LR = 0.63 (±0.05) log L[O III] + 0.67 (±0.03) log M after including all the LLAGN detected at high resolution at 15 GHz, and the best-studied hard-state X-ray binaries (luminosities are given in erg s−1 while the masses are in units of solar mass). Finally, we find conclusive evidence that the nuclear 15 GHz radio luminosity function (RLF) of all the detected Palomar Sample LLAGN has a turnover at the low-luminosity end, and is best-fitted with a broken power law. The break in the power law occurs at a critical mass accretion rate of 1.2 × 10−3 M⊙ yr−1, which translates to an Eddington ratio of ṁEdd ~ 5.1 × 10−5, assuming a black hole mass of 109 M⊙. The local group stands closer to the extrapolation of the higher-luminosity sources, and the classical Seyferts agree with the nuclear RLF of the LLAGN in the local universe.

scholarly journals Non-Thermal Emission from Radio-Loud AGN Jets: Radio vs. X-rays

Galaxies ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 6
Author(s):  
Elena Fedorova ◽  
Bohdan Hnatyk ◽  
Antonino Del Popolo ◽  
Anatoliy Vasylenko ◽  
Vadym Voitsekhovskyi
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Thermal Emission ◽  
Galactic Nuclei ◽  
X Rays ◽  
X Ray ◽  
Compact Source ◽  
Central Engine ◽  
Sky Survey ◽  
Inverse Compton

We consider the sample of 55 blazars and Seyferts cross-correlated from the Planck all-sky survey based on the Early Release Compact Source Catalog (ERCSC) and Swift BAT 105-Month Hard X-ray Survey. The radio Planck spectra vs. X-ray Swift/XRT+BAT spectra of the active galactic nuclei (AGN) sample were fitted with the simple and broken power law (for the X-ray spectra taking into account also the Galactic neutral absorption) to test the dependencies between the photon indices of synchrotron emission (in radio range) and synchrotron self-Compton (SSC) or inverse-Compton emission (in X-rays). We show that for the major part of the AGN in our sample there is a correspondence between synchrotron and SSC photon indices (one of two for broken power-law model) compatible within the error levels. For such objects, this can give a good perspective for the task of distinguishing between the jet base counterpart from that one emitted in the disk-corona AGN “central engine”.

scholarly journals Blueshifted absorption lines from X-ray reflection in IRAS 13224−3809

2020 ◽  
Vol 493 (2) ◽  
pp. 2518-2522 ◽  
Author(s):  
A C Fabian ◽  
C S Reynolds ◽  
J Jiang ◽  
C Pinto ◽  
L C Gallo ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Absorption Lines ◽  
Narrow Line ◽  
X Ray ◽  
Absorbing Layer ◽  
Reflection Component

ABSTRACT We explore a disc origin for the highly blueshifted, variable absorption lines seen in the X-ray spectrum of the narrow-line Seyfert 1 galaxy IRAS 13224−3809. The blueshift corresponds to a velocity of ∼0.25c. Such features in other active galactic nuclei are often interpreted as ultrafast outflows. The velocity is of course present in the orbital motions of the inner disc. The absorption lines in IRAS 13224−3809 are best seen when the flux is low and the reflection component of the disc is strong relative to the power-law continuum. The spectra are consistent with a model in which the reflection component passes through a thin, highly ionized absorbing layer at the surface of the inner disc, the blueshifted side of which dominates the flux due to relativistic aberration (the disc inclination is about 70°). No fast outflow need occurs beyond the disc.

scholarly journals Soft X-ray Spectra of Seyfert Galaxies

1989 ◽  
Vol 134 ◽  
pp. 173-174
Author(s):  
C. M. Urry ◽  
J. S. Kruper ◽  
C. R. Canizares
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Spectral Indices ◽  
X Ray

The first X-ray (2–10 keV) spectral surveys of active galactic nuclei (AGN) were remarkably uniform, with spectral indices narrowly distributed about α=0.65, independent of radio-emitting properties or X-ray luminosity (Mushotzky 1984). In the few AGN detected above 20 keV, this canonical power law extended to at least 50 keV (Rothschild et al. 1983, Pounds 1985, Worrall et al. 1980; Halpern 1982; Worrall and Marshall 1984). In practice these surveys were dominated by low luminosity Seyfert 1 galaxies.

scholarly journals Individual optical variability of active galactic nuclei from the MEXSAS2 sample

2020 ◽  
Vol 499 (4) ◽  
pp. 6053-6065
Author(s):  
M Laurenti ◽  
F Vagnetti ◽  
R Middei ◽  
M Paolillo
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Individual Variability ◽  
Optical Variability ◽  
Data Set ◽  
X Ray ◽  
Bolometric Luminosity ◽  
The Individual ◽  
Physical Quantities

ABSTRACT At present, most of the variability studies of active galactic nuclei (AGNs) are based on ensemble analyses. Nevertheless, it is interesting to provide estimates of the individual variability properties of each AGN, in order to relate them with intrinsic physical quantities. A useful data set is provided by the Catalina Surveys Data Release 2 (CSDR2), which encompasses almost a decade of photometric measurements of ∼500 million objects repeatedly observed hundreds of times. We aim to investigate the individual optical variability properties of 795 AGNs originally included in the Multi-Epoch XMM Serendipitous AGN Sample 2 (MEXSAS2). Our goals consist of (i) searching for correlations between variability and AGN physical quantities and (ii) extending our knowledge of the variability features of MEXSAS2 from the X-ray to the optical. We use the structure function (SF) to analyse AGN flux variations. We model the SF as a power law, $\text{SF}(\tau)=A\, (\tau /\tau _0)^\gamma$, and we compute its variability parameters. We introduce the V-correction as a simple tool to correctly quantify the amount of variability in the rest frame of each source. We find a significant decrease of variability amplitude with increasing bolometric, optical and X-ray luminosity. We obtain the indication of an intrinsically weak positive correlation between variability amplitude and redshift, z. Variability amplitude also appears to be positively correlated with αox. The slope of the power-law SF, γ, is weakly correlated with the bolometric luminosity Lbol and/or with the black hole mass MBH. When comparing optical to X-ray variability properties, we find that X-ray variability amplitude is approximately the same for those AGNs with larger or smaller variability amplitude in the optical. On the contrary, AGNs with steeper SF in the optical do present steeper SF in the X-ray, and vice versa.

Polarization Variability of Active Galactic Nuclei and X‐Ray Binaries

1997 ◽  
Vol 487 (1) ◽  
pp. 142-152 ◽  
Author(s):  
Gang Bao ◽  
Petr Hadrava ◽  
Paul J. Wiita ◽  
Ying Xiong
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
X Ray ◽  
X Ray Binaries
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