Results 31 to 40 of about 771 (176)
How Are Red and Blue Quasars Different? The Radio Properties
Galaxies, 2021 A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the majority of cases) that the accretion disc is obscured by a column of dust which extinguishes the shorter-wavelength blue emission. In this paper, we summarize recent
Victoria A. Fawcett +3 more
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Optically Quiet Quasars – Radio and Optical Investigations [PDF]
Symposium - International Astronomical Union, 1994 The activity in the nuclei of bright galaxies could arise from a number of sources: they may contain compact variable radio sources, they may be strong IR/optical/X–ray continuum sources, or they may have strong emission lines. Usually but not always these properties go together as in radio loud quasars.
Chidi E. Akujor +3 more
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Accretion and star formation in ‘radio-quiet’ quasars [PDF]
Proceedings of the International Astronomical Union, 2019 AbstractRadio observations allow us to identify a wide range of active galactic nuclei (AGN), which play a significant role in the evolution of galaxies. Amongst AGN at low radio-luminosities is the ‘radio-quiet’ quasar (RQQ) population, but how they contribute to the total radio emission is under debate, with previous studies arguing that it is ...
White, Sarah +6 more
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Radio and Optical Observations of “Optically Quiet Quasars” [PDF]
Symposium - International Astronomical Union, 1986 In recent years a number of very steep spectrum, compact radio sources have been discovered (e.g. Cotton 1983, Cotton and Owen 1985, Ulvestad 1985) which have no optical counterpart to the limit of the Palomar Sky Survey. VLBI observations of a number of these have confirmed the very compact (<10 mas) nature of several of these sources.
W. D. Cotton, F. N. Owen, M. J. Mahoney
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Extreme accretion events: TDEs and changing‐look AGN
Astronomische Nachrichten, Volume 344, Issue 4, May 2023., 2023 Abstract We present a review of the topics of X‐ray stellar tidal disruption events (TDEs) and changing‐look active galactic nuclei (AGN). Stars approaching a supermassive black hole (SMBH) can be tidally disrupted and accreted. TDEs were first discovered in the X‐ray regime and appear as luminous, giant‐amplitude flares from inactive galaxies.
S. Komossa, D. Grupe
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Dependence of the Radio Emission on the Eddington Ratio of Radio-quiet Quasars
The Astrophysical Journal, 2022 Abstract Roughly 10% of quasars are “radio-loud,” producing copious radio emission in large jets. The origin of the low-level radio emission seen from the remaining 90% of quasars is unclear. Observing a sample of eight radio-quiet quasars with the Very Long Baseline Array, we discovered that their radio properties depend strongly on ...
Abdulla Alhosani +6 more
openaire +2 more sources
Metal Content in Relativistically Jetted and Radio-Quiet Quasars in the Main Sequence Context
Galaxies, 2023 The optical and UV properties of radio-quiet (RQ) and radio-loud (RL, relativistically “jetted”) active galactic nuclei (AGN) are known to differ markedly; however, it is still unclear what is due to a sample selection and what is associated with ...
Paola Marziani +3 more
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Astronomische Nachrichten, Volume 344, Issue 4, May 2023., 2023 Abstract The non‐linear correlation between the UV and X‐ray emission observed in active galactic nuclei remains a puzzling question that challenges accretion models. While the UV emission originates from the cold disk, the X‐ray emission is emitted by a hot corona whose physical characteristics and geometry are still highly debated.
S. Barnier +3 more
wiley +1 more source
The Astrophysical Journal, 2023 We present polarization-sensitive images from the Karl G. Jansky Very Large Array (VLA) at 5 GHz of 11 radio-quiet PG quasars. Based on the radio morphology, spectral index, and polarization properties from the VLA study, coupled with the findings of our
Silpa S. +3 more
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The road toward imaging a black hole: A personal perspective
Natural Sciences, Volume 2, Issue 4, October 2022., 2022 The article describes the authors personal journey towards developig the Event Horizon Telescope and the first image of a black hole. Left: predcition made by the author and collaborators proposing the black hole imaging in 2000. Right: the two images observed and published by the Event Horizon Telescope in 2019 and 2022.
Heino Falcke
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