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Published December 2016 | Submitted + Published
Journal Article Open

The F-GAMMA programme: multi-frequency study of active galactic nuclei in the Fermi era. Programme description and the first 2.5 years of monitoring


Context. To fully exploit the scientific potential of the Fermi mission for the physics of active galactic nuclei (AGN), we initiated the F-GAMMA programme. 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 performed monthly monitoring of 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-yr data set 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 flat-spectrum radio quasars (FSRQs), BL Lacertae objects (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, 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.

Additional Information

© 2016 ESO. Received 23 December 2015; Accepted 4 August 2016; Published online 28 November 2016. The authors would like to thank the anonymous referee for the very careful reading of the manuscript, and the constructive and insightful comments. They have noticeably improved the quality of the paper. We would also like to thank the MPIfR internal referees Drs J. Hodgson and C. Casadio for the careful reading of the manuscript. This research is based on observations with the 100 m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg. It has also made use of observations with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). I.N., V.K., and I.M. were funded by the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Universities of Bonn and Cologne. The OVRO 40 m programme is supported in part by NASA grants NNX08AW31G and NNG06GG1G and NSF grant AST-0808050. We would like to acknowledge partial support from the EU FP7 Grant PIRSES- GA-2012-316788.

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Submitted - 1608.02580.pdf


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