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Register a new userMulti-band properties of superluminal AGN detected by Fermi/LAT
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Tigran Arshakian Dr
Publication date
2010
fields
Physics
and research's language is
English
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We perform a multi-band statistical analysis of core-dominated superluminal active galactic nuclei (AGN) detected with Fermi Large Area Telescope (LAT). The detection rate of $gamma$-ray jets is found to be high for optically bright AGN. There is a significant correlation between the $gamma$-ray luminosity and the optical nuclear and radio (15 GHz) luminosities of AGN. We report a well defined positive correlation between the $gamma$-ray luminosity and the radio-loudness for quasars and BL Lacertae type objects (BL Lacs). The slope of the best-fit line is significantly different for quasars and BL Lacs. The relations between the optical and radio luminosities and the $gamma$-ray loudness are also examined, showing a different behavior for the populations of quasars and BL Lacs. Statistical results suggest that the $gamma$-ray, optical and radio emission is generated at different locations and velocity regimes along the parsec-scale jet.
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Aims. We use a sample of 83 core-dominated active galactic nuclei (AGN) selected from the MOJAVE (Monitoring of Jets in AGN with VLBA Experiments) radio-flux-limited sample and detected with the Fermi Large Area Telescope (LAT) to study the relations between non-simultaneous radio, optical, and gamma-ray measurements. Methods. We perform a multi-band statistical analysis to investigate the relations between the emissions in different bands and reproduce these relations by modeling of the spectral energy distributions of blazars. Results. There is a significant correlation between the gamma-ray luminosity and the optical nuclear and radio (15 GHz) luminosities of blazars. We report a well defined positive correlation between the gamma-ray luminosity and the radio-optical loudness for quasars and BL Lacertae type objects (BL Lacs). A strong positive correlation is found between the radio luminosity and the gamma-ray-optical loudness for quasars, while a negative correlation between the optical luminosity and the gamma-ray-radio loudness is present for BL Lacs. Modeling of these correlations with a simple leptonic jet model for blazars indicates that variations of the accretion disk luminosity (and hence the jet power) is able to reproduce the trends observed in most of the correlations. To reproduce all observed correlations, variations of several parameters, such as the accretion power, jet viewing angle, Lorentz factor, and magnetic field of the jet, are required.
The third catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (3LAC) is presented. It is based on the third catalog (3FGL,cite{3FGL}) of sources detected with a test statistic greater than 25, using the first 4 years of data. The 3LAC includes 1591 AGNs located at high ($|b|>10^circ$) Galactic latitudes (with 28 duplicate associations, thus corresponding to 1563 gamma-ray sources among 2192 sources in the 3FGL catalog), providing $71%$ more sources with respect to the 2FGL. Various properties, such as gamma-ray fluxes and photon power law spectral indices, redshifts, gamma-ray luminosities, variability, and their correlations are presented and discussed for the different blazar and non-blazar classes.
Active galactic nuclei (AGNs) have been attracting research attention due to their special observable properties. Specifically, a majority of AGNs are detected by Fermi-LAT missions, but not by Fermi-LAT, which raises the question of whether any differences exist between the two. To answer this issue, we compile a sample of 291 superluminal AGNs (189 FDSs and 102 non-FDSs) from available multi-wavelength radio, optical, and X-ray (or even $gamma$-ray) data and Doppler factors and proper motion ($mu$) (or apparent velocity ($beta_{rm{app}}$)); calculated the apparent velocity from their proper motion, Lorentz factor ($Gamma$), viewing angle ($phi$) and co-moving viewing angle ($phi_{co}$) for the sources with available Doppler factor ($delta$); and performed some statistical analyses for both types. Our study indicated that1. In terms of average values, FDSs have higher proper motions ($mu$), apparent velocities ($beta_{rm app}$), Doppler factor ($delta$), Lorentz factor ($Gamma$), and smaller viewing angle ($phi$). Nevertheless, there is no clear difference in co-moving viewing angles ($phi_{rm co}$).
Although the Fermi mission has increased our knowledge of gamma-ray AGN, many questions remain, such as the site of gamma-ray production, the emission mechanism, and the factors that govern the strength of the emission. Using data from a high radio band, 37 GHz, uncontaminated by other radiation components besides the jet emission, we study these questions with averaged flux densities over the the first year of Fermi operations. We look for possible correlations between the 100 MeV - 100 GeV band used by the Fermi satellite and 37 GHz radio band observed at the Aalto University Metsahovi Radio Telescope, as well as for differences between the gamma-ray emission of different AGN subsamples. We use data averaged over the 1FGL period. Our sample includes 249 northern AGN, including a complete sample of 68 northern AGN with a measured average flux density exceeding 1 Jy. We find significant correlation between both the flux densities and luminosities in gamma and radio bands. The Fermi luminosity is inversely correlated with the peak frequency of the synchrotron component of the AGN spectral energy distributions. We also calculate the gamma dominances, defined as the ratio between the gamma and radio flux densities, and find an indication that high-energy blazars are more gamma-dominated than low-energy blazars. After studying the distributions of gamma and radio luminosities, it is clear that BL Lacertae objects are different from quasars, with significantly lower luminosities. It is unclear whether this is an intrinsic difference, an effect of variable relativistic boosting across the synchrotron peak frequency range, or the result of Fermi being more sensitive to hard spectrum sources like BL Lacertae objects. Our results suggest that the gamma radiation is produced co-spatially with the 37 GHz emission, i.e., in the jet.
Blazars are a small fraction of all extragalactic sources but, unlike other objects, they are strong emitters across the entire electromagnetic spectrum. Recent data in the microwave region of the electromagnetic spectrum have become available to allow for systematic studies of blazars over large cosmological volumes. This frequency band is indeed particularly suited for the selection of blazars since at these frequencies the contamination from radio extended components with steep spectra is no longer present and the emission from the accretion process is negligible. During the first 3 months of scientific operations Fermi-LAT detected 106 bright, high-galactic latitude (| b |> 10 deg) AGNs with high significance. In this study we investigate the possible relations between the microwave and the gamma-ray emissions for Fermi-LAT detected AGNs belonging to WMAP 5th year bright source catalog.
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