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

Kovalev, Y. Y.; Nizhelsky, N. A.; Bogdantsov, A. B.

doi:10.1071/as01109

Cited by 56 publications

(52 citation statements)

References 12 publications

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“…Aller 1970;Aller et al 1985), the monitoring at the Medicina/Noto 32-m telescopes (5, 8, 22 GHz;Bach et al 2007), and the RATAN-600 monitoring (1-22 GHz; Kovalev et al 2002); all at lower radio frequencies. At intermediate frequencies, the Metsähovi Radio Observatory program (22 & 37 GHz; e.g.…”

Section: Blazars Viewed At Angles Not Larger Than 10mentioning

confidence: 99%

The F-GAMMA programme: multi-frequency study of active galactic nuclei in theFermiera

Fuhrmann

Angelakis

Zensus

et al. 2016

A&A

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Context. To fully exploit the scientific potential of the Fermi mission for AGN physics, we initiated the F-GAMMA program. Between 2007 and 2015 the F-GAMMA was the prime provider of complementary multi-frequency monitoring in the radio regime. Aims. We quantify the radio variability of γ-ray blazars. We investigate its dependence on source class and examine whether the radio variability is related to the γ-ray loudness. Finally, we assess the validity of a putative correlation between the two bands. Methods. The F-GAMMA monitored monthly a sample of about 60 sources at up to twelve radio frequencies between 2.64 and 228.39 GHz. We perform a time series analysis on the first 2.5-year dataset to obtain variability parameters. A maximum likelihood analysis is used to assess the significance of a correlation between radio and γ-ray fluxes.Results. We present light curves and spectra (coherent within ten days) obtained with the Effelsberg 100-m and IRAM 30-m telescopes. All sources are variable across all frequency bands with amplitudes increasing with frequency up to rest frame frequencies of around 60-80 GHz as expected by shock-in-jet models. Compared to FSRQs, BL Lacs show systematically lower variability amplitudes, brightness temperatures and Doppler factors at lower frequencies, while the difference vanishes towards higher ones. The time scales appear similar for the two classes. The distribution of spectral indices appears flatter or more inverted at higher frequencies for BL Lacs. Evolving synchrotron self-absorbed components can naturally account for the observed spectral variability. We find that the Fermi-detected sources show larger variability amplitudes as well as brightness temperatures and Doppler factors, than non-detected ones. Flux densities at 86.2 and 142.3 GHz correlate with 1 GeV fluxes at a significance level better than 3σ, implying that γ rays are produced very close to the mm-band emission region.

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Section: Blazars Viewed At Angles Not Larger Than 10mentioning

confidence: 99%

The F-GAMMA programme: multi-frequency study of active galactic nuclei in theFermiera

Fuhrmann

Angelakis

Zensus

et al. 2016

A&A

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“…We use spectra of 4047 sources observed with RATAN from 1997 to 2006 during multifrequency monitoring and survey campaigns conducted by Kovalev et al (1999Kovalev et al ( , 2000Kovalev et al ( , 2002. The observed source list includes a complete sample of sources with δ > −30 and a total VLBI flux density at 8 GHz greater than 200 mJy (Kovalev et al 2007).…”

Section: Observational Data and Sample Selectionmentioning

confidence: 99%

A sample of GHz‐peaked spectrum sources selected at RATAN‐600: Spectral and variability properties

et al. 2009

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We describe a new sample of 226 GPS (GHz-Peaked Spectrum) source candidates selected using simultaneous 1-22 GHz multi-frequency observations with the RATAN-600 radio telescope. Sixty objects in our sample are identified as GPS source candidates for the first time. The candidates were selected on the basis of their broad-band radio spectra only. We discuss the spectral and variability properties of selected objects of different optical classes.

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“…7 The sources in this figure are placed such that the contribution of the compact component to the total emission increases from left to right. According to Kovalev et al (2002), we interpret the broadband spectra of all selected sources as a sum of two constituents: emission from an optically thin, extended component with a steep spectrum that usually increases with decreasing frequency up to hundreds of megahertz, and emission from a compact component with self-absorption that has a maximum at a frequency higher than 1 GHz. The spectrum of J0012+6551 has spectral index À0.5.…”

Section: The Vcs3 Catalogmentioning

confidence: 99%

The Third VLBA Calibrator Survey: VCS3

Petrov¹,

Kovalev²,

Fomalont³

et al. 2005

Self Cite

154

168

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

Cited by 56 publications

References 12 publications

The F-GAMMA programme: multi-frequency study of active galactic nuclei in theFermiera

The F-GAMMA programme: multi-frequency study of active galactic nuclei in theFermiera

A sample of GHz‐peaked spectrum sources selected at RATAN‐600: Spectral and variability properties

The Third VLBA Calibrator Survey: VCS3

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