A Connection Between Apparent VLBA Jet Speeds and Initial Active Galactic Nucleus Detections Made by the Fermi Gamma-Ray Observatory

In its first three months of operations, the Fermi Gamma-Ray Observatory has detected approximately one quarter of the radio-flux-limited MOJAVE sample of bright flat-spectrum active galactic nuclei (AGNs) at energies above 100 MeV. We have investigated the apparent parsec-scale jet speeds of 26 MOJ...

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Bibliographic Details
Published in:The Astrophysical journal 2009-05, Vol.696 (1), p.L22-L26
Main Authors: Lister, M. L, Homan, D. C, Kadler, M, Kellermann, K. I, Kovalev, Y. Y, Ros, E, Savolainen, T, Zensus, J. A
Format: Article
Language:English
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Summary:In its first three months of operations, the Fermi Gamma-Ray Observatory has detected approximately one quarter of the radio-flux-limited MOJAVE sample of bright flat-spectrum active galactic nuclei (AGNs) at energies above 100 MeV. We have investigated the apparent parsec-scale jet speeds of 26 MOJAVE AGNs measured by the Very Long Baseline Array (VLBA) that are in the LAT bright AGN sample (LBAS). We find that the g-ray bright quasars have faster jets on average than the non-LBAS quasars, with a median of 15c, and values ranging up to 34c. The LBAS AGNs in which the LAT has detected significant g-ray flux variability generally have faster jets than the nonvariable ones. These findings are in overall agreement with earlier results based on nonuniform EGRET data which suggested that g-ray bright AGNs have preferentially higher Doppler boosting factors than other blazar jets. However, the relatively low LAT detection rates for the full MOJAVE sample (24%) and previously known MOJAVE EGRET-detected blazars (43%) imply that Doppler boosting is not the sole factor that determines whether a particular AGN is bright at g-ray energies. The slower apparent jet speeds of LBAS BL Lac objects and their higher overall LAT detection rate as compared to quasars suggest that the former are being detected by Fermi because of their higher intrinsic (unbeamed) g-ray to radio luminosity ratios.
ISSN:1538-4357
0004-637X
1538-4357
DOI:10.1088/0004-637X/696/1/L22