Survey of instantaneous 1-22 GHz spectra of 550 compact
extragalactic objects with declinations from $-30^\circ$ to $+43^\circ$

Kovalev, Y. Y.; Nizhelsky, N. A.; Kovalev, Yu. A.; Berlin, Asher; Жеканис, Г. В.; Мингалиев, М. Г.; Bogdantsov, A. V.

doi:10.1051/aas:1999406

Cited by 110 publications

(101 citation statements)

References 11 publications

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“…As the 1.4 GHz NVSS and 325 MHz WENSS images show that the nearest neighbour is at a distance of 232 arcsec from J1606+3124 and based on the probabilities of the sources 6 http://third.ucllnl.org/cgi-bin/firstcutout being side lobes, we conclude that the five neighbouring sources in the 1.4 GHz FIRST image are all image artefacts. We matched J1606+3124 to sources in the 0.96, 2.3, 3.9, 7.7, 11.2 and 21.65 GHz catalogues of Kovalev et al (1999) and the 1.1, 2.3, 4.8, 7.7, 11.2 and 21.7 GHz catalogues of Mingaliev et al (2012). However, since these observations were taken with the RATAN-600 telescope, the resolution of all of the observations is lower than the distance to the nearest neighboring source.…”

Section: J1606+3124mentioning

confidence: 99%

Radio spectra of bright compact sources at z>4.5

Coppejans

Velzen

Intema

et al. 2017

Mon. Not. R. Astron. Soc.

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High-redshift quasars are important to study galaxy and active galactic nuclei (AGN) evolution, test cosmological models, and study supermassive black hole growth. Optical searches for high-redshift sources have been very successful, but radio searches are not hampered by dust obscuration and should be more effective at finding sources at even higher redshifts. Identifying high-redshift sources based on radio data is, however, not trivial. Here we report on new multi-frequency Giant Metrewave Radio Telescope (GMRT) observations of eight z > 4.5 sources previously studied at high angular resolution with very long baseline interferometry (VLBI). Combining these observations with those from the literature, we construct broad-band radio spectra of all 30 z > 4.5 sources that have been observed with VLBI. In the sample we found flat, steep and peaked spectra in approximately equal proportions. Despite several selection effects, we conclude that the z > 4.5 VLBI (and likely also non-VLBI) sources have diverse spectra and that only about a quarter of the sources in the sample have flat spectra. Previously, the majority of high-redshift radio sources were identified based on their ultra-steep spectra (USS). Recently a new method has been proposed to identify these objects based on their megahertz-peaked spectra (MPS). Neither method would have identified more than 18 per cent of the high-redshift sources in this sample. More effective methods are necessary to reliably identify complete samples of high-redshift sources based on radio data.

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Section: J1606+3124mentioning

confidence: 99%

Radio spectra of bright compact sources at z>4.5

Coppejans

Velzen

Intema

et al. 2017

Mon. Not. R. Astron. Soc.

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“…Since many flat-spectrum sources are variable, the estimates of the spectral index made at different epochs may be unreliable. Instantaneous 1-22 GHz broadband spectra at four to six frequencies for 3000 active galactic nuclei with flux densities greater than 100 mJy at 2.3 GHz and > À0:5, including many sources from this list, were observed with the 600 m ring radio telescope RATAN-600 of the Russian Academy of Sciences in transit mode as a part of an ongoing survey program (see Kovalev et al 1999 for the method of observation and data reduction). All flat-spectrum sources from this sample with flux densities greater than 200 mJy at X or S band and not previously observed with VLBI, a total of 116 sources, were included in the list of VCS3 candidates.…”

Section: Source Selectionmentioning

confidence: 99%

The Third VLBA Calibrator Survey: VCS3

Petrov¹,

Kovalev²,

Fomalont³

et al. 2005

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We present the third extension to the Very Long Baseline Array (VLBI ) Calibrator Survey, containing 360 new sources not previously observed with very long baseline interferometry (VLBI). The survey, based on three 24 hour VLBA observing sessions, fills the areas on the sky above declination À45 where the calibrator density is less than one source within a 4 radius disk at any given direction. The positions were derived from astrometric analysis of the group delays determined at 2.3 and 8.6 GHz frequency bands using the CALC/SOLVE software package. The VCS3 catalog of source positions, plots of correlated flux density versus length of projected baseline, and contour plots and FITS files of naturally weighted CLEAN images, as well as calibrated visibility function files, are available electronically from the Goddard Geodetic VLBI Group.

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“…In 1997 March we started the program for a sample of about 550 compact extragalactic sources with correlated flux density F c > 0.1 Jy at 13 cm from the Preston et al (1985) VLBI survey in the declination range from −30 • to +43 • . Results of the observations made in 1997 December, the list of the sources included in the monitoring, description of the method of observations and data processing are presented in Kovalev et al (1999). Horizontal localisation of the stationary antenna horns allows broad-band spectral responses to be obtained at all observed frequencies in a time of 1-2 min in the transit mode of meridional observations.…”

Section: Observationsmentioning

confidence: 99%

Broad-band Radio Spectra Variability of 550 AGN in 1997-2001

Kovalev

Nizhelsky

Bogdantsov

2002

Publ. – Astron. Soc. Aust

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Results are presented of long-term monitoring at the radio telescope RATAN–600 and a model interpretation of instantaneous 1–22 GHz spectra at six frequencies for a sample of 550 compact extragalactic radio sources. The sources are selected from the Preston et al. (1985) VLBI survey and are located in the declination range from −30° to +43°. Dependence of the index of variability on frequency is analysed for different subsamples. Factors of flux density variations range from 1 to 15. A typical behaviour of spectra evolution during strong radio outbursts in various objects is recognised suggesting a common physical nature of the variability. Invoking VLBI observations in spectra–structure analysis, we find that usually more than 70% of the total emission is coming from the mas scale at frequencies higher than 5 GHz. The observed variability can be explained in the model with a relativistic jet of parsec scale in the longitudinal magnetic field or in the shock-in-jet model.

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Survey of instantaneous 1-22 GHz spectra of 550 compact extragalactic objects with declinations from $-30^\circ$ to $+43^\circ$

Cited by 110 publications

References 11 publications

Radio spectra of bright compact sources at z>4.5

Radio spectra of bright compact sources at z>4.5

The Third VLBA Calibrator Survey: VCS3

Broad-band Radio Spectra Variability of 550 AGN in 1997-2001

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