Gamma-Ray and Parsec-Scale Jet Properties of a Complete Sample of Blazars From the MOJAVE Program

Astrophysical Journal - ASTROPHYS J 07/2011; 742. DOI: 10.1088/0004-637X/742/1/27
Source: arXiv

ABSTRACT We investigate the Fermi LAT gamma-ray and 15 GHz VLBA radio properties of a
joint gamma-ray- and radio-selected sample of AGNs obtained during the first 11
months of the Fermi mission (2008 Aug 4 - 2009 Jul 5). Our sample contains the
brightest 173 AGNs in these bands above declination -30 deg. during this
period, and thus probes the full range of gamma-ray loudness (gamma-ray to
radio band luminosity ratio) in the bright blazar population. The latter
quantity spans at least four orders of magnitude, reflecting a wide range of
spectral energy distribution (SED) parameters in the bright blazar population.
The BL Lac objects, however, display a linear correlation of increasing
gamma-ray loudness with synchrotron SED peak frequency, suggesting a universal
SED shape for objects of this class. The synchrotron self-Compton model is
favored for the gamma-ray emission in these BL Lacs over external seed photon
models, since the latter predict a dependence of Compton dominance on Doppler
factor that would destroy any observed synchrotron SED peak - gamma-ray
loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are
distinguished by lower than average radio core brightness temperatures, and
none display large radio modulation indices or high linear core polarization
levels. No equivalent trends are seen for the flat-spectrum radio quasars
(FSRQ) in our sample. Given the association of such properties with
relativistic beaming, we suggest that the HSP BL Lacs have generally lower
Doppler factors than the lower-synchrotron peaked BL Lacs or FSRQs in our


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Eduardo Ros