Global Jet Watch

Abstract:

We have observed 17 sources in a complete sample of FRIs in nearby UGC galaxies with the VLBA at 1.67 GHz. We detect core-jets in 60% and twin-jets in 10%. The data (alignment, sidedness ratios, detection statistics) are consistent with relativistic Doppler boosting effects. The luminosity per unit length of the jets fades with distance l from the core as L-j proportional to l(-2). The fading is not consistent with either deceleration of the jets (with subsequent reduction of Doppler boosting) or synchrotron losses. However, the fading can be explained by adiabatic losses in a constant velocity jet with constant opening angle and magnetic field perpendicular to the jet axis. If confirmed by VLBA polarimetry, this would imply that the jets must decelerate on scales larger than tens of parsec.

Abstract:

We present new results on magnetized accretion discs launching bipolar, self-collimated jets. We show that the jet mass-loading depends critically on the disc vertical equilibrium. In particular, it is strongly influenced by any entropy generation occurring at the disc surface. Discs around supermassive black holes and close to a magnetohydrostatic balance have the potential to produce mildly relativistic jets.

Abstract:

Analytical relations between the mean jet speed and the mean jet flux asymmetry and between their variances are derived in the context of a unified scheme. The mean jet speeds of classical double radio sources axe estimated by using the asymmetry of jet-counter-Jet flux densities taken from the 3CRR and B2 samples. For FRI radio sources the mean jet speed is similar to 0.54 +/- 0.03c, while for FRII low-redshift radio galaxies and intermediate-redshift quasars the values found are similar to 0.4c +/- 0.06c and greater than or equal to 0.6c respectively.

Abstract:

The quasar PKS 0405-385 exhibits episode's of unusually strong hourly variability at 8.6, 4.8, 2.4 and 1.4 GHz. These variations, seen first in June 1996, ceased after several weeks, but reappeared in November 1998 and were monitored closely at the. ATCA. We argue that our data are in agreement with interstellar scintillation of a source component which is a few micro-arcseconds in size. This claim is further supported by our recent finding of the time delay in the variability pattern measured between the ATCA and the VLA.

Abstract:

We extend the model of Blandford & Payne (1982) for magnetocentrifugally driven winds by presenting solutions that satisfy the singularity conditions at all critical surfaces. In these solutions, the asymptotic supercritical zone is causally disconnected from the upstream region,of the outflow, unlike the,situation in previous studies.