Jet opening angles and gamma-ray brightness of AGN

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 P 0 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.

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

“…The source shows a compact core-dominated structure, with a resolved nuclear region which contains about 98% of the total flux density in the image. The weak and extended jet feature, J1, located at about 4 mas separation from the nucleus has a peak brightness of ≈15 mJy/beam, which is not surprising considering energy losses due to adiabatic expansion of the flow up to the estimated deprojected linear separation of 2.3 kpc of this feature from the core of the source (assuming the jet viewing angle of 0.8 • ; Pushkarev et al 2009). The linear separation can be a factor of ∼3.5 smaller, if the observed misalignment of ≈2 • between the position angles of C2 and J1 reflects the physical change of the jet direction.…”

Multiwavelength observations of the γ-ray flaring quasar S4 1030+61 in 2009–2014

“…Considering 2φ ≃ 0.26Γ −1 (Pushkarev et al 2009), the magnetic field strength estimate at 1 pc is of 2.2 G. The magnetic field strength in the core at observed frequency can be found as…”

From the ‘blazar sequence' to unification of blazars and radio galaxies

“…The bulk Lorentz factors of Nemmen et al (2012) were collected from the results of Pushkarev et al (2009) (the number ∼20%). For blazars without Γvar obtained from Pushkarev et al (2009), they used the power-law fit of f b ≈ 5 × 10 −4 (L obs 49 ) −0.39±0.15 as an estimator for f b (significant level at the 3.6σ; L obs 49 is observation γ-ray luminosity). Moreover, making use of the relation between cavity power and extended radio 300 MHz luminosity and assuming Pjet = Pcav, they estimated the jet kinetic power.…”

“…The Doppler corrections of synchrotron peak frequency and luminosity scale as ν ′ = ν/δ and L ′ peak = L peak /δ P respectively, with P = 3 + α for a moving, isotropic source and P = 2 + α for a continuous jet (δ is Doppler factor; spectral index α = 1; Urry &Padovani 1995 andNieppola et al 2008). Since blazars obey θj < 1/Γ, especially for Fermi blazars (Jorstad et al 2005;Pushkarev et al 2009;Linford et al 2011;Wu et al 2014), we assume δ ∼ Γ (Γ is estimated from radio observation or beaming factor f b ). From the above relations, Doppler-corrected peak luminosity and frequency can be obtained (D 2 -correction and D 3 -correction stand for P = 2 + α and P = 3 + α respectively).…”