On X-ray emission lines from active galactic nuclei and disk models

AbstractThrough X-ray observations with ASCA, low-luminosity active galactic nuclei have been found in at least seven near-by spiral galaxies. Some of them exhibit very intense, and possibly broad, Fe-K emission lines. Their time variability is relatively insignificant, in contrast to lowluminosity Seyfert galaxies.

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High-Energy Lines in Active Galactic Nuclei

International Astronomical Union Colloquium ◽

10.1017/s0252921100039567 ◽

1997 ◽

Vol 159 ◽

pp. 20-33

Author(s):

Hagai Netzer

Keyword(s):

Active Galactic Nuclei ◽

Column Density ◽

Limit Of Detection ◽

Galactic Nuclei ◽

Diffuse Radiation ◽

High Energy ◽

Emission Lines ◽

Absorption Lines ◽

Oxygen Absorption ◽

X Ray

AbstractThe recent observations of a highly ionized, X-ray absorbing gas in active galactic nuclei (AGN) suggest a new nuclear component, the so-called ‘warm absorber’. This gas is likely to be at a temperature of ~ 1–2 × 105 K and is most easily detected in the 0.5–10keV range, where several oxygen absorption edges are often observed.This review describes the properties of warm absorbers and the relation to other nuclear components, such as the broad-line emitting gas. The stability of the gas is a key issue and analysis shows that it is likely to be thermally stable, at the above mentioned temperature. When successful models are compared to the data, they can be used to infer the column density, composition and level of ionization of the X-ray absorbing gas. They also show that, on top of the strong continuum absorption, the gas must emit X-ray lines that are at the limit of detection by present day X-ray instruments.New calculations of X-ray emission lines emitted by ionized X-ray absorbers are shown and discussed. Various line equivalent widths are defined and examples are shown over a large range of column density and ionization parameter. The equivalent width of the strongest 0.5-5 keV lines is only a few tens of eV, but in cases of obscured X-ray source, like in Seyfert 2s, the lines are measured against the scattered and diffuse radiation with much larger equivalent widths. The X-ray absorbing and emitting gas is responsible also for a fraction of the observed flux of some UV emission lines. It is also the cause of the detection of several UV absorption lines. The calculations predict that some of those absorption lines, in particular 0 VI λ1035, are very sensitive warm-absorber tracers. Thus, analysis of the combined X-ray and UV properties is the best way to identify the location and properties of this gas.Understanding the origin and properties of warm X-ray absorbers is a major challenge of AGN research. Several new ideas are briefly discussed, trying to relate the location, mass, and motion of this gas to what is known about other observed nuclear components.

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Soft X-ray emission lines in the X-ray binary Swift J1858.6–0814 observed with XMM–Newton Reflection Grating Spectrometer: disc atmosphere or wind?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2258 ◽

2020 ◽

Vol 498 (1) ◽

pp. 68-76 ◽

Cited By ~ 1

Author(s):

D J K Buisson ◽

D Altamirano ◽

M Díaz Trigo ◽

M Mendez ◽

M Armas Padilla ◽

...

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Accretion Disc ◽

Emission Lines ◽

X Ray ◽

Grating Spectrometer ◽

Optical Wavelengths ◽

X Ray Binaries ◽

Ionization Parameter ◽

Reflection Grating

ABSTRACT We find soft X-ray emission lines from the X-ray binary Swift J1858.6–0814 in data from XMM–NewtonReflection Grating Spectrometer (RGS): N vii, O vii, and O viii, as well as notable residuals short of a detection at Ne ix and other higher ionization transitions. These could be associated with the disc atmosphere, as in accretion disc corona sources, or with a wind, as has been detected in Swift J1858.6–0814 in emission lines at optical wavelengths. Indeed, the N vii line is redshifted, consistent with being the emitting component of a P-Cygni profile. We find that the emitting plasma has an ionization parameter log (ξ) = 1.35 ± 0.2 and a density n > 1.5 × 1011 cm−3. From this, we infer that the emitting plasma must be within 1013 cm of the ionizing source, ∼5 × 107 rg for a 1.4 M⊙ neutron star, and from the line width that it is at least 104 rg away [2 × 109(M/1.4 M⊙) cm]. We compare this with known classes of emission-line regions in other X-ray binaries and active galactic nuclei.

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Polarization Variability of Active Galactic Nuclei and X‐Ray Binaries

The Astrophysical Journal ◽

10.1086/304575 ◽

1997 ◽

Vol 487 (1) ◽

pp. 142-152 ◽

Cited By ~ 9

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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Gamma-Ray and Neutrino Signals from Accretion Disk Coronae of Active Galactic Nuclei

Galaxies ◽

10.3390/galaxies9020036 ◽

2021 ◽

Vol 9 (2) ◽

pp. 36

Author(s):

Yoshiyuki Inoue ◽

Dmitry Khangulyan ◽

Akihiro Doi

Keyword(s):

Active Galactic Nuclei ◽

Gamma Ray ◽

Galactic Nuclei ◽

High Energy ◽

Thermal Activity ◽

X Ray ◽

Cascade Models ◽

Coronal Activity ◽

Ngc 1068 ◽

High Energy Particles

To explain the X-ray spectra of active galactic nuclei (AGN), non-thermal activity in AGN coronae such as pair cascade models has been extensively discussed in the past literature. Although X-ray and gamma-ray observations in the 1990s disfavored such pair cascade models, recent millimeter-wave observations of nearby Seyferts have established the existence of weak non-thermal coronal activity. In addition, the IceCube collaboration reported NGC 1068, a nearby Seyfert, as the hottest spot in their 10 yr survey. These pieces of evidence are enough to investigate the non-thermal perspective of AGN coronae in depth again. This article summarizes our current observational understanding of AGN coronae and describes how AGN coronae generate high-energy particles. We also provide ways to test the AGN corona model with radio, X-ray, MeV gamma ray, and high-energy neutrino observations.

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Hot gaseous atmospheres of rotating galaxies observed with XMM–Newton

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3182 ◽

2020 ◽

Vol 499 (4) ◽

pp. 5163-5174

Author(s):

A Juráňová ◽

N Werner ◽

P E J Nulsen ◽

M Gaspari ◽

K Lakhchaura ◽

...

Keyword(s):

Angular Momentum ◽

Active Galactic Nuclei ◽

Spiral Galaxy ◽

Galactic Nuclei ◽

X Ray ◽

Hot Gas ◽

Heating And Cooling ◽

Theoretical Predictions ◽

Central Regions ◽

Gaseous Atmospheres

ABSTRACT X-ray emitting atmospheres of non-rotating early-type galaxies and their connection to central active galactic nuclei have been thoroughly studied over the years. However, in systems with significant angular momentum, processes of heating and cooling are likely to proceed differently. We present an analysis of the hot atmospheres of six lenticulars and a spiral galaxy to study the effects of angular momentum on the hot gas properties. We find an alignment between the hot gas and the stellar distribution, with the ellipticity of the X-ray emission generally lower than that of the optical stellar emission, consistent with theoretical predictions for rotationally supported hot atmospheres. The entropy profiles of NGC 4382 and the massive spiral galaxy NGC 1961 are significantly shallower than the entropy distribution in other galaxies, suggesting the presence of strong heating (via outflows or compressional) in the central regions of these systems. Finally, we investigate the thermal (in)stability of the hot atmospheres via criteria such as the TI- and C-ratio, and discuss the possibility that the discs of cold gas present in these objects have condensed out of the hot atmospheres.

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