Mark III VLBI Observations of the Nucleus of M81 at 2.3 and 8.3 GHz

The normal spiral galaxy M81, which has some characteristics of a Seyfert (Peimbert, Torres-Peimbert, 1981), has a flat spectrum in the radio range (de Bruyn et al., 1976), variable on the time scale of days (Crane et al., 1976), and detectable radiation at infrared (Rieke, Lebofsky, 1978) and X-ray wavelengths (Elvis, van Speybroeck, 1981). At a distance of ∼3.3 Mpc, M81 is the nearest extragalactic object with a nucleus detectable with VLBI (Kellermann et al., 1976). We report here on simultaneous VLBI observations made with the Mark III system at 2.3 and 8.3 GHz. Observations on 14 and 16 March 1981 utilized the 100 m diameter telescope in Effelsberg, W. Germany (MPIR); the 43 m telescope at Green Bank, WV (NRAO); and the 40 m telescope near Big Pine, CA (OVRO).

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Star/Disk Interaction in the Nuclei of Active Galaxies

International Astronomical Union Colloquium ◽

10.1017/s0252921100039646 ◽

1997 ◽

Vol 159 ◽

pp. 64-65

Author(s):

D.N.C. Lin

Keyword(s):

Time Scale ◽

Velocity Dispersion ◽

Rotation Speed ◽

Accretion Rate ◽

X Ray ◽

Definitive Evidence ◽

Vlbi Observations ◽

Disk Evolution ◽

Spatial Locations ◽

Maser Sources

The most definitive evidence for an accretion disk is provided by the discovery of megamasers (Claussen et al. 1984) which appear to be located in a molecular torus around the nucleus of the mildly active galaxy NGC 4258. Confirmation of Keplerian rotation speed was obtained from radio interferometer (Nakai et al. 1993) and VLBI observations (Greenhill, this volume). Based on the correlation between the spatial locations and radial velocities of the masers, Moran et al. (1995) deduced that the masers are located in a disk at radii R = 0.13–0.26 pc around a black hole with a mass M ≈ 3.5 × 107M⊙ (Watson & Wallin 1994, Maoz 1995). A limit on the thickness (H < 2.5 × 10−3R) is deduced from the velocity dispersion of the maser sources. The mass-diffusion time scale is estimated to be τd > 1015 α−1 s, where α is the viscosity parameter. An efficient angular-momentum transfer mechanism (α > 0.1) is needed for τd ≈ 108 yr, which is the disk evolution time scale inferred from the correlation between interacting galaxies and intense AGN activities (MacKenty 1989, Hernquist 1989). A relatively large value of a is also required to account for the accretion rate needed to power the X-ray flux of NGC 4258.

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Evidence of Relativistic Beaming in BL Lac-Type Objects

Symposium - International Astronomical Union ◽

10.1017/s0074180900078025 ◽

1984 ◽

Vol 110 ◽

pp. 187-188

Author(s):

Diana M. Worrall

Keyword(s):

Radio Emission ◽

Time Scale ◽

Source Region ◽

Model Fitting ◽

X Ray ◽

Extragalactic Object ◽

Relativistic Beaming ◽

International Ultraviolet Explorer ◽

Bl Lac ◽

Separate Source

Multifrequency observations of a variable extragalactic object, when all acquired within the inferred variability time scale of the source, can provide clues to the source's energy mechanisms. A guest observer program with the International Ultraviolet Explorer satellite has provided the focus for such measurements of a few BL Lac-type and related objects at frequencies in the radio, mm, IR, visual and UV. Earlier-epoch X-ray measurements are included in subsequent model fitting. This paper summarizes some of the observations in this program. Synchrotron self-Compton (SSC) models are then applied to the data, leading to the conclusions that the objects are relativistically beamed and that radio emission, at least below a frequency of ~20 GHz, is from a separate source region.

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VLBI Observations of an Expanding Jet in Cygnus X-3

Symposium - International Astronomical Union ◽

10.1017/s0074180900134692 ◽

1988 ◽

Vol 129 ◽

pp. 279-280

Author(s):

Lawrence A. Molnar ◽

M. J. Reid ◽

J. E. Grindlay

Keyword(s):

Time Scale ◽

Particle Injection ◽

X Ray ◽

Physical Conditions ◽

Vlbi Observations ◽

Important Clue ◽

Relativistic Jet ◽

Extragalactic Jets ◽

Injection Mechanism ◽

Rare Opportunity

The X-ray binary Cyg X-3 offers a rare opportunity to study the physical conditions of the formation of a relativistic jet. While the central engines of extragalactic jets are generally poorly understood, the infrared and X-ray data on Cyg X-3 allow detailed modelling of the conditions in the inner disk and corona, the source of the jet energy. Study of the periodic nature of particle injection into the jet may yield an important clue to the nature of the particle injection mechanism. And the time scale of jet evolution is much shorter than for extragalactic sources, allowing the possibility of observing a large number of flares to determine general characteristics.

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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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The frequency of Kozai–Lidov disc oscillation driven giant outbursts in Be/X-ray binaries

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2250 ◽

2019 ◽

Vol 489 (2) ◽

pp. 1797-1804 ◽

Cited By ~ 2

Author(s):

Rebecca G Martin ◽

Alessia Franchini

Keyword(s):

Orbital Period ◽

Time Scale ◽

Orbital Plane ◽

Material Flows ◽

X Ray ◽

System Parameters ◽

Be Star ◽

Chaotic Nature ◽

X Ray Binaries ◽

Good Agreement

ABSTRACT Giant outbursts of Be/X-ray binaries may occur when a Be-star disc undergoes strong eccentricity growth due to the Kozai–Lidov (KL) mechanism. The KL effect acts on a disc that is highly inclined to the binary orbital plane provided that the disc aspect ratio is sufficiently small. The eccentric disc overflows its Roche lobe and material flows from the Be star disc over to the companion neutron star causing X-ray activity. With N-body simulations and steady state decretion disc models we explore system parameters for which a disc in the Be/X-ray binary 4U 0115+634 is KL unstable and the resulting time-scale for the oscillations. We find good agreement between predictions of the model and the observed giant outburst time-scale provided that the disc is not completely destroyed by the outburst. This allows the outer disc to be replenished between outbursts and a sufficiently short KL oscillation time-scale. An initially eccentric disc has a shorter KL oscillation time-scale compared to an initially circular orbit disc. We suggest that the chaotic nature of the outbursts is caused by the sensitivity of the mechanism to the distribution of material within the disc. The outbursts continue provided that the Be star supplies material that is sufficiently misaligned to the binary orbital plane. We generalize our results to Be/X-ray binaries with varying orbital period and find that if the Be star disc is flared, it is more likely to be unstable to KL oscillations in a smaller orbital period binary, in agreement with observations.

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A new jet/outflow maser in the nucleus of the Compton-thick AGN IRAS 15480-0344

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317010596 ◽

2017 ◽

Vol 13 (S336) ◽

pp. 129-132

Author(s):

Paola Castangia ◽

Andrea Tarchi ◽

Alessandro Caccianiga ◽

Paola Severgnini ◽

Gabriele Surcis ◽

...

Keyword(s):

Detection Rate ◽

Radio Continuum ◽

Continuum Emission ◽

Maser Emission ◽

X Ray ◽

Vlbi Observations ◽

S0 Galaxies ◽

Water Maser

AbstractInvestigations of H2O maser galaxies at X-ray energies reveal that most harbor highly absorbed AGN. Possible correlations between the intrinsic X-ray luminosity and the properties of water maser emission have been suggested. With the aim of looking into these correlations on a more solid statistical basis, we have search for maser emission in a well-defined sample of Compton-thick AGN. Here we report the results of the survey, which yielded a surprisingly high maser detection rate, with a particular focus on the newly discovered luminous water maser in the lenticular (field) S0 galaxy IRAS 15480-0344. Recently, VLBI observations have been obtained to image the line and continuum emission in the nucleus of this galaxy. The radio continuum emission at VLBI scales is resolved into two compact components that are interpreted as jet knots. Based on the single-dish profile, the variability of the maser emission, and the position of the maser spots with respect to these continuum sources, we favor of a jet/outflow origin for the maser emission, consistent with similar cases found in other radio-quiet AGN. This scenario is consistent with the hypothesis of the presence of strong nuclear winds recently invoked to explain the main characteristics of field S0 galaxies.

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