The VSOP 5 GHz Active Galactic Nucleus Survey. IV. The Angular Size/Brightness Temperature Distribution

Horiuchi, S.; Fomalont, Ed; Scott, Asher; Lovell, J. E. J.; Moellenbrock, G.; Dodson, Richard; Murata, Yasuhiro; Hirabayashi, H.; Edwards, P. G.; Gurvits, L. I.; Shen, Zhi

doi:10.1086/424811

Cited by 60 publications

(62 citation statements)

References 29 publications

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“…A typical core size of 0.2 mas would still produce only very low X-ray fluxes. A size of ∼0.1 mas or smaller, which is the case in only a small fraction of AGN (Horiuchi et al 2004), is needed to produce a flux comparable to the 10 −13 erg cm −2 s −1 diffuse flux. If the source is a newly-awoken AGN, X-ray emission from additional processes to synchrotron self-Compton are likely to be present, however, many examples of low luminosity AGN with X-ray luminosities of < 10 41 erg s −1 exist, equating to a flux of < 10 −15 erg cm −2 s −1 at the distance of NGC 660 (Terashima & Wilson 2003).…”

Section: A New Period Of Agn Activitymentioning

confidence: 99%

A new period of activity in the core of NGC 660

Argo

Bemmel

Connolly

et al. 2015

Mon. Not. R. Astron. Soc.

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The core of the nearby galaxy NGC 660 has recently undergone a spectacular radio outburst; using a combination of archival radio and Chandra X-ray data, together with new observations, the nature of this event is investigated. Radio observations made using e-MERLIN in mid-2013 show a new compact and extremely bright continuum source at the centre of the galaxy. High angular resolution observations carried out with the European VLBI Network show an obvious jet-like feature to the north east and evidence of a weak extension to the west, possibly a counter-jet. We also examine high angular resolution Hi spectra of these new sources, and the radio spectral energy distribution using the new wide-band capabilities of e-MERLIN. We compare the properties of the new object with possible explanations, concluding that we are seeing a period of new AGN activity in the core of this polar ring galaxy.

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Section: A New Period Of Agn Activitymentioning

confidence: 99%

A new period of activity in the core of NGC 660

Argo

Bemmel

Connolly

et al. 2015

Mon. Not. R. Astron. Soc.

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“…We have also used additional observations made in 1998 and 1999 by L. I. Gurvits et al (2006, in preparation) as part of a separate program to compare 15 GHz source structure measured with the VLBA to 5 GHz structure measured in the framework of the VSOP survey program (Hirabayashi et al 2000;Lovell et al 2004;Scott et al 2004;Horiuchi et al 2004). The program by Gurvits et al used the same observing and data reduction procedures as the VLBA 15 GHz monitoring survey and provides both additional sources and additional epochs.…”

Section: Sample Definitionmentioning

confidence: 99%

“…In column (8) we indicate whether or not the radio source is associated with a gamma-ray detection by EGRET Sowards-Emmerd et al 2003. Columns (9) and (10) indicate whether or not the source is a member of the complete correlated flux density-limited MOJAVE sample and the VSOP 5 GHz AGN survey source sample (Hirabayashi et al 2000;Lovell et al 2004;Scott et al 2004;Horiuchi et al 2004). Column (11) gives references to papers reporting the intraday variability (IDV ) of the source total flux density.…”

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confidence: 99%

“…Col. (9): Indicator for the correlated flux density-limited MOJAVE sample (see x 2). Col. (10): Indicator for the VSOP 5 GHz AGN survey sample, where A = the VSOP AGN survey sample observed with VSOP, B = the VSOPAGN survey sample not yet observed with VSOP, C = the VSOPAGN survey sample too faint to be observed with VSOP ( Horiuchi et al [2004] have analyzed sample members A and C; in the latter case, 5 GHz VLBA data only were used), and PR = the Pearson-Readhead VSOP survey sample . Col. (11): References reporting on the fast variations from the source on timescales less than 2-3 days.…”

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Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine-Scale Structure

et al. 2005

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We have examined the compact structure in 250 flat-spectrum extragalactic radio sources using interferometric fringe visibilities obtained with the Very Long Baseline Array ( VLBA) at 15 GHz. With projected baselines out to 440 Mk, we are able to investigate source structure on typical angular scales as small as 0.05 mas. This scale is similar to the resolution of the VLBI Space Observatory Programme data obtained on longer baselines at a lower frequency and with somewhat poorer accuracy. For 171 sources in our sample, more than half of the total flux density seen by the VLBA remains unresolved on the longest baselines. There are 163 sources in our list with a median correlated flux density at 15 GHz in excess of 0.5 Jy on the longest baselines; these will be useful as fringe finders for shortwavelength VLBA observations. The total flux densities recovered in the VLBA images at 15 GHz are generally close to the values measured around the same epoch at the same frequency with the RATAN-600 and University of Michigan Radio Astronomy Observatory telescopes.We have modeled the core of each source with an elliptical Gaussian component. For about 60% of the sources, we have at least one observation in which the core component appears unresolved (generally smaller than 0.05 mas) in one direction, usually transverse to the direction into which the jet extends. BL Lac objects are on average more compact than quasars, while active galaxies are on average less compact. Also, in an active galaxy the submilliarcsecond core component tends to be less dominant. Intraday variability (IDV) sources typically have a more compact, more core-dominated structure on sub-milliarcsecond scales than non-IDV sources, and sources with a greater amplitude of intraday variations tend to have a greater unresolved VLBA flux density. The objects known to be GeV gamma-ray-loud appear to have a more compact VLBA structure than the other sources in our sample. This suggests that the mechanisms for the production of gamma-ray emission and for the generation of compact radio synchrotron-emitting features are related. The brightness temperature estimates and lower limits for the cores in our sample typically range between 10 11 and 10 13 K, but they extend up to 5 ; 10 13 K, apparently in excess of the equipartition brightness temperature or the inverse Compton limit for stationary synchrotron sources. The largest component speeds are observed in radio sources with high observed brightness temperatures, as would be expected from relativistic beaming. Longer baselines, which can be obtained by space VLBI observations, will be needed to resolve the most compact high brightness temperature regions in these sources.

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“…One of the core goals of the VSOP Survey imaging program was to measure lower limits to the brightness temperatures (T b ) directly from the data (c.f. Horiuchi et al 2004). The determined T b (from VLBI) depends only on the physical baseline length, independent of frequency, so space baselines will always provide the highest possible limits.…”

Section: Introductionmentioning

confidence: 99%

The VSOP Survey: final aggregate results

et al. 2006

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Abstract. In February 1997 the Japanese radio astronomy satellite HALCA was launched to provide the space-borne element for the VSOP mission. HALCA provided linear baselines three-times greater than that of ground arrays, thus providing higher resolution and higher AGN brightness temperature measurements and limits. Twenty-five percent of the scientific time of the mission was devoted to the "VSOP survey" of bright, compact, extra-galactic radio sources at 5 GHz. A complete list of 294 survey targets were selected from pre-launch surveys, 91% of which were observed during the satellite's lifetime.The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure, to provide a source list for use with future space VLBI missions, and to compare radio properties with other data throughout the electro-magnetic spectrum. All the data collected have now been analysed and is being prepared for the final image Survey paper. In this paper we present details of the mission, and some statistics of the images and brightness temperatures.

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The VSOP 5 GHz Active Galactic Nucleus Survey. IV. The Angular Size/Brightness Temperature Distribution

Cited by 60 publications

References 29 publications

A new period of activity in the core of NGC 660

A new period of activity in the core of NGC 660

Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine-Scale Structure

The VSOP Survey: final aggregate results

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