50 <i>μ</i>as resolution VLBI images of AGN's at <i>λ</i>3 mm

Rantakyrö, Fredrik T.; Bååth, Lars B.; Backer, D. C.; Booth, R. S.; Carlstrom, J. E.; Emerson, D. T.; Grewing, M.; Hirabayashi, H.; Hodges, Mark; Inoue, M.; Kobayashi, H.; Krichbaum, T. P.; Kus, A. J.; Moran, J. M.; Morimoto, Manabu

doi:10.1051/aas:1998282

Cited by 27 publications

(9 citation statements)

References 48 publications

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“…We suggest that the model explored in this paper has applicability to the stationary, unresolved, flat spectrum components revealed with milli-arcsecond VLBI observations, now an established technique for revealing moving and evolving synchrotronemitting jet knots (e.g. Gómez et al 2000;Jorstad et al 2005;Ly et al 2007), and even revealed with global VLBI techniques with 10s of micro-arcsecond resolution (Rantakyro et al 1998).…”

Section: Correlated Radio and Optical/uv Emissionmentioning

confidence: 90%

“…In many subsequent observations of many different objects there has been no direct observational evidence supporting this paradigm and indirect evidence against it, even under the scrutiny of sub-milliarcsec, multi-epoch observations (e.g. Gómez et al 2000;Jorstad et al 2005;Ly et al 2007;Rantakyro et al 1998). There is simply no evidence in support of multiple self-absorbed components which conveniently have successively higher turnover frequencies to explain the overall integrated spectral properties of stationary cores.…”

Section: Beyond Cosmic Conspiracy Theorymentioning

confidence: 99%

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On the Origin of Radio Core Emission in Radio-quiet Quasars

Blundell

Kuncic

2007

ApJ

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We present a model for the radio emission from radio-quiet quasar nuclei. We show that a thermal origin for the high brightness temperature, flat spectrum point sources (known as radio "cores") is possible provided the emitting region is hot and optically-thin. We hence demonstrate that opticallythin bremsstrahlung from a slow, dense disk wind can make a significant contribution to the observed levels of radio core emission. This is a much more satisfactory explanation, particularly for sources where there is no evidence of a jet, than a sequence of self-absorbed synchrotron components which collectively conspire to give a flat spectrum. Furthermore, such core phenomena are already observed directly via milli-arcsecond radio imaging of the Galactic microquasar SS 433 and the active galaxy NGC 1068. We contend that radio-emitting disk winds must be operating at some level in radioloud quasars and radio galaxies as well (although in these cases, observations of the radio cores are frequently contaminated/dominated by synchrotron emission from jet knots). This interpretation of radio core emission mandates mass accretion rates that are substantially higher than Eddington. Moreover, acknowledgment of this mass-loss mechanism as an AGN feedback process has important implications for the input of energy and hot gas into the inter-galactic medium (IGM) since it is considerably less directional than that from jets.

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Section: Correlated Radio and Optical/uv Emissionmentioning

confidence: 90%

Section: Beyond Cosmic Conspiracy Theorymentioning

confidence: 99%

On the Origin of Radio Core Emission in Radio-quiet Quasars

Blundell

Kuncic

2007

ApJ

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“…The emission can be asymmetric due to Doppler shifts associated with rapid rotation (or inflow/outflow) near the black hole. The size of this shadow is within less than a factor of two of the maximum resolution already achieved by sub-mm VLBI (∼ 50µas, Rantakyro et al 1998). It may also be feasible to do polarimetric imaging at mm and sub-mm wavelengths, which would reveal additional effects of strong gravity distortions .…”

Section: Figure 20mentioning

confidence: 91%

The Supermassive Black Hole at the Galactic Center

Melia

Falcke

2001

Annu. Rev. Astron. Astrophys.

479

416

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The inner few parsecs at the Galactic Center have come under intense scrutiny in recent years, in part due to the exciting broad-band observations of this region, but also because of the growing interest from theorists motivated to study the physics of black hole accretion, magnetized gas dynamics and unusual star formation. The Galactic Center is now known to contain arguably the most compelling supermassive black hole candidate, weighing in at a little over 2.6 million suns. Its interaction with the nearby environment, comprised of clusters of evolved and young stars, a molecular dusty ring, ionized gas streamers, diffuse hot gas, and a hypernova remnant, is providing a wealth of accretion phenomenology and high-energy processes for detailed modeling. In this review, we summarize the latest observational results, and focus on the physical interpretation of the most intriguing object in this region---the compact radio source Sgr A*, thought to be the radiative manifestation of the supermassive black hole.Comment: Annual Review of Astronomy & Astrophysics, Vol. 39 (2001), in press, 48 pages, 20 figures (partially in reduced quality), also available at http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#gcrevie

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“…Sensitive VLBI observations at 86 GHz have been made for several sources, including 3C 111 (Doeleman & Claussen 1997), 3C 454.3 (Krichbaum et al 1995(Krichbaum et al , 1999Pagels et al 2004), NRAO 150 (Agudo et al 2007), NRAO 530 (Bower et al 1997), M87 (Krichbaum et al 2006), 3C 273 and3C 279 (Attridge 2001). In order to increase the number of objects imaged at 86 GHz, four detection and imaging surveys were conducted during the 1990s, with a total of 124 extragalactic radio sources observed (see Beasley et al 1997;Lonsdale et al 1998;Rantakyro et al 1998;Lobanov et al 2000). In these surveys, fringes were detected of 44 objects, but only 24 radio sources have been successfully imaged.…”

Section: Introductionmentioning

confidence: 99%

A Global 86 GHZ Vlbi Survey of Compact Radio Sources

Lee

Lobanov

Krichbaum

et al. 2008

The Astronomical Journal

133

189

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We present results from a large 86 GHz global VLBI survey of compact radio sources. The main goal of the survey is to increase by factors of 3-5 the total number of objects accessible for future 3-mm VLBI imaging. The survey observations reach the baseline sensitivity of 0.1 Jy and image sensitivity of better than 10 mJy/beam. The total of 127 compact radio sources have been observed. The observations have yielded images for 109 sources, extending the database of the sources imaged at 86 GHz with VLBI observation by a factor of 5, and only 6 sources have not been detected. The remaining 12 objects have been detected but could not be imaged due to insufficient closure phase information. Radio galaxies are less compact than quasars and BL Lacs on submilliarcsecond scale. Flux densities and sizes of core and jet components of all imaged sources have been estimated using Gaussian model fitting. From these measurements, brightness temperatures have been calculated, taking into account resolution limits of the data. The cores of 70% of the imaged sources are resolved. The core brightness temperatures of the sources peak at ∼ 10 11 K and only 1% have brightness temperatures higher than 10 12 K. Cores of Intraday Variable (IDV) sources are smaller in angular size than non-IDV sources, and so yield higher brightness temperatures.Every source in the sample was observed for 3-4 scans of 7-minute duration (snapshot mode). Although the uv-coverage of such an experiment limits the dynamic range and structural sensitivity of images, the large number of the participating antennas gives a sufficient uv-coverage of the sources at low and high declinations ( Figure 2). The data were recorded either with 128-MHz or 64-MHz bandwidth using the MkIV VLBI system with 1-and 2-bit sampling adopted at different epochs.The observations were made in lefthand circular polarization (LCP). Three to four scans per hour were recorded, using the time between the scans for antenna focusing, pointing and calibration. The data were correlated using the MkIV correlator of the Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn (Alef & Müskens 2001). Data ProcessingIn this section, we describe the post-correlation processing of the 3 mm-VLBI survey datasets. Fringes were searched in two steps using HOPS (Haystack Observatory Postprocessing System) and AIPS (The NRAO Astronomical Image Processing System). In the first step, the HOPS task fourfit was used to precisely determine phase-residuals. The first fourfit was run with a wide search window (e.g. a width of 1 µsec for singleband delay, 2 µsec for multiband delay and 500 psec sec −1 for delay rate) centered at zero in delay. Since the fourfit produces baseline-based fringe solutions, the mean and standard deviation of the detected fringe solutions on each baseline were estimated and served as the offset and width of the search window for the second fourfit. The detected fringe solutions from the second run were used to interpolate the offset of the singleband delay for nondetected scans. In the f...

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50 μas resolution VLBI images of AGN's at λ3 mm

Cited by 27 publications

References 48 publications

On the Origin of Radio Core Emission in Radio-quiet Quasars

On the Origin of Radio Core Emission in Radio-quiet Quasars

The Supermassive Black Hole at the Galactic Center

A Global 86 GHZ Vlbi Survey of Compact Radio Sources

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