2010 Pushkarev, A. B. AGN的喷流张角和Lorentz因子

主要内容:
最后有个表格，其中alpha是喷流张角，还有观测角，Lorentz因子。
居然有Gamma和alpha成反比这个现象。
观测角基本上总是比喷流的张角大(alpha_int)。
张角还有看上去的张角和内禀张角之分。

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Title:		Jet opening angles and gamma-ray brightness of AGN
Authors:		Pushkarev, A. B.; Kovalev, Y. Y.; Lister, M. L.; Savolainen, T.
Affiliation:		AA(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany ; Pulkovo Astronomical Observatory, Pulkovskoe Chaussee 65/1, 196140 St. Petersburg, Russia; Crimean Astrophysical Observatory, 98688 Nauchny, Crimea, Ukraine apushkar@mpifr.de), AB(Astro Space Center of Lebedev Physical Institute, Profsoyuznaya 86/32, 117997 Moscow, Russia; Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), AC(Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907, USA), AD(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany)
Publication:		Astronomy and Astrophysics, Volume 507, Issue 2, 2009, pp.L33-L36 (A&A Homepage)
Publication Date:		11/2009
Origin:		EDP Sciences
Astronomy Keywords:		galaxies: active, galaxies: jets, quasars: general, radio continuum: galaxies
DOI:		10.1051/0004-6361/200913422
Bibliographic Code:		2009A&A...507L..33P

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 P_ext lies within the range 1.1 to 34.6, with a best fit estimate of P_0/P_ext≈ 2. Table [see full text] is only available in electronic form at http://www.aanda.org

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