Abstract
Aims: We have investigated the differences in apparent opening angles
between the parsec-scale jets of the active galactic nuclei (AGN)
detected by the Fermi Large Area Telescope during its first three months
of operations and those of non-LAT-detected AGN. Methods: We used
15.4 GHz VLBA observations of sources from the 2 cm VLBA MOJAVE program,
a subset of which comprises the statistically complete flux density
limited MOJAVE sample. We determined the apparent opening angles by
analyzing transverse jet profiles from the data in the image plane and
by applying a model fitting technique to the data in the (u,v) plane.
Both methods provided comparable opening angle estimates. Results: The apparent opening angles of γ-ray bright blazars are
preferentially larger than those of γ-ray weak sources. At the
same time, we have found the two groups to have similar intrinsic
opening angle distributions, based on a smaller subset of sources. This
suggests that the jets in γ-ray bright AGN are oriented at
preferentially smaller angles to the line of sight resulting in a
stronger relativistic beaming. The intrinsic jet opening angle and the
bulk flow Lorentz factor are found to be inversely proportional, as
predicted by standard models of compact relativistic jets. If a gas
dynamical jet acceleration model is assumed, the ratio of the initial
pressure of the plasma in the core region P0 to the external
pressure Pext lies within the range 1.1 to 34.6, with a best
fit estimate of P_0/P_ext≈ 2.
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Original language | English |
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Pages (from-to) | 33-36 |
Journal | Astronomy and Astrophysics |
Volume | 507 |
Issue number | 2 |
DOIs | |
Publication status | Published - 2009 |
MoE publication type | A1 Journal article-refereed |
Keywords
- galaxies: active
- galaxies: jets
- quasars: general
- radio continuum: galaxies