scholarly journals Astrotomography

2011 ◽  
Vol 7 (S285) ◽  
pp. 227-234
Author(s):  
Keith Horne ◽  
Raymundo Baptista ◽  
Misty C. Bentz ◽  
Danny Steeghs
Keyword(s):  
Active Galactic Nuclei ◽  
Imaging Techniques ◽  
Binary Star ◽  
Galactic Nuclei ◽  
Rotating Stars ◽  
Time Resolved ◽  
Accretion Flows ◽  
Compact Binary ◽  
Doppler Shifts ◽  
Rapidly Rotating Stars

AbstractAstrotomography refers to a suite of indirect imaging techniques that achieve micro-arcsecond angular resolution by measuring projections obtained from time-resolved spectroscopic observations. The projections arise from Doppler shifts, eclipses or time delays, combined with rotation of the star or binary system being imaged. At our workshop we reviewed and discussed state-of-the-art methods for imaging the surfaces and magnetic fields of rapidly rotating stars, the accretion flows in compact binary star systems and the broad emission-line regions in active galactic nuclei.

scholarly journals The X-ray emission in young radio active galactic nuclei

2020 ◽  
Vol 497 (1) ◽  
pp. 482-497
Author(s):  
Mai Liao ◽  
Minfeng Gu ◽  
Minhua Zhou ◽  
Liang Chen
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Spectral Energy ◽  
Strongly Correlated ◽  
Strong Correlations ◽  
X Ray ◽  
Accretion Flows ◽  
Combining Data ◽  
Vlbi Data ◽  
5 Ghz

ABSTRACT In this work, we investigated the X-ray emission for a sample of young radio active galactic nuclei (AGNs) by combining data from Chandra/XMM–Newton with data for other wavebands. We find strong correlations between the X-ray luminosity LX at 2–10 keV and the radio luminosities LR at 5 GHz for the VLBI radio-core, VLA radio-core and Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) component, indicating that both parsec- and kiloparsec-scale radio emissions are strongly correlated with X-ray emission in these sources. We find an approximately linear dependence of the radio on the X-ray luminosity in the sources with radiatively efficient accretion flows (i.e. the Eddington ratio Redd ≳ 10−3), with b ∼ 1 ($L_{\rm R}\, \propto \, L_{\rm X} ^{b}$) and $\xi _{\rm RX}\, \sim$ 1 in the fundamental plane using the VLBI data. The dependence is consistent with the re-analysed results of a previous study of Fan and Bai at Redd ≳ 10−3, but is significantly different from the theoretical prediction of accretion flow as the origin of X-ray emission. In contrast to the case for radio-quiet quasars, there is no significant correlation between Γ and the Eddington ratio. Our results seem to indicate that the X-ray emission of high-accretion young radio AGNs may be from the jet. We constructed the spectral energy distributions (SEDs) for 18 sources (most of which are in radiatively efficient accretion), namely nine galaxies and nine quasars with high-quality X-ray data, and find that the X-ray emission of most quasars is more luminous than that of normal radio-quiet quasars. This is clearly seen from the quasar composite SED, in which the X-ray emission is apparently higher than that of radio-quiet quasars, probably supporting jet-related X-ray emission in young radio AGNs. The possibility that the X-ray emission is from self-synchrotron Compton is discussed.

scholarly journals Time-resolved infrared emission from radiation-driven central obscuring structures in active galactic nuclei

2014 ◽  
Vol 445 (4) ◽  
pp. 3878-3891 ◽  
Author(s):  
M. Schartmann ◽  
K. Wada ◽  
M. A. Prieto ◽  
A. Burkert ◽  
K. R. W. Tristram
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Infrared Emission ◽  
Time Resolved

scholarly journals Soft gamma rays from low accreting supermassive black holes and connection to energetic neutrinos

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shigeo S. Kimura ◽  
Kohta Murase ◽  
Péter Mészáros
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Hadronic Interactions ◽  
Neutrino Detectors ◽  
Accretion Flows ◽  
Diffuse Background ◽  
The Universe

AbstractThe Universe is filled with a diffuse background of MeV gamma-rays and PeV neutrinos, whose origins are unknown. Here, we propose a scenario that can account for both backgrounds simultaneously. Low-luminosity active galactic nuclei have hot accretion flows where thermal electrons naturally emit soft gamma rays via Comptonization of their synchrotron photons. Protons there can be accelerated via turbulence or reconnection, producing high-energy neutrinos via hadronic interactions. We demonstrate that our model can reproduce the gamma-ray and neutrino data. Combined with a contribution by hot coronae in luminous active galactic nuclei, these accretion flows can explain the keV – MeV photon and TeV – PeV neutrino backgrounds. This scenario can account for the MeV background without non-thermal electrons, suggesting a higher transition energy from the thermal to nonthermal Universe than expected. Our model is consistent with X-ray data of nearby objects, and testable by future MeV gamma-ray and high-energy neutrino detectors.

scholarly journals Resolving accretion flows in nearby active galactic nuclei with the Event Horizon Telescope

2019 ◽  
Vol 490 (4) ◽  
pp. 4606-4621
Author(s):  
Bidisha Bandyopadhyay ◽  
Fu-Guo Xie ◽  
Neil M Nagar ◽  
Dominik R G Schleicher ◽  
Venkatessh Ramakrishnan ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Event Horizon ◽  
Spectral Energy Distribution ◽  
Galactic Nuclei ◽  
Integration Time ◽  
Spectral Energy ◽  
Model Parameters ◽  
Jet Formation ◽  
Accretion Flows ◽  
Long Baseline

ABSTRACT The Event Horizon Telescope (EHT), now with its first ever image of the photon ring around the supermassive black hole of M87, provides a unique opportunity to probe the physics of supermassive black holes through Very Long Baseline Interferometry (VLBI), such as the existence of the event horizon, the accretion processes as well as jet formation in low-luminosity AGNs (LLAGNs). We build a theoretical model that includes an advection dominated accretion flow (ADAF) with emission from thermal and non-thermal electrons in the flow and a simple radio jet outflow. The predicted spectral energy distribution (SED) of this model is compared to sub-arcsec resolution observations to get the best estimates of the model parameters. The model-predicted radial emission profiles at different frequency bands are used to predict whether the inflow can be resolved by the EHT or with telescopes such as the Global 3-mm VLBI array (GMVA). In this work the model is initially tested with high-resolution SED data of M87 and then applied to our sample of five galaxies (Cen A, M84, NGC 4594, NGC 3998, and NGC 4278). The model then allows us to predict if one can detect and resolve the inflow for any of these galaxies using the EHT or GMVA within an 8 h integration time.

Clumpy accretion flows in active galactic nuclei: X-ray variability and spectral properties

2010 ◽  
Author(s):  
W. Ishibashi ◽  
T. J.-L. Courvoisier ◽  
A. Comastri ◽  
L. Angelini ◽  
M. Cappi
Keyword(s):  
Active Galactic Nuclei ◽  
Spectral Properties ◽  
Galactic Nuclei ◽  
X Ray ◽  
Accretion Flows

scholarly journals Low‐Luminosity Active Galactic Nuclei at the Highest Resolution: Jets or Accretion Flows?

2004 ◽  
Vol 603 (1) ◽  
pp. 42-50 ◽  
Author(s):  
James M. Anderson ◽  
James S. Ulvestad ◽  
Luis C. Ho
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Accretion Flows
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