Global Jet Watch

Abstract:

The X-ray emission in many clusters of galaxies shows a central peak in surface brightness coincident with a drop in temperature. These characterize a cooling flow. There is also often a radio source at the centre of such a region. Data from Chandra now enable us to map the interaction between the radio source and the intracluster medium. Preliminary work shows no sign of heating of the gas beyond the radio lobes, which are often devoid of cooler gas and so appear as holes. In the case of the Perseus cluster around 3C 84, the coolest X-ray emitting gas occurs immediately around the inner radio lobes.

Abstract:

Optical spectra of the narrow, disturbed, interface regions between radio jets and gas clouds in the interstellar medium of the host galaxies of two nearby radio sources have diagnostic (BPT) diagrams for line ratios of [NII], [OIII], [SII], Halpha and Hbeta which are inconsistent with published models for shock heating, as well as those for photoionization/excitation by either a "hard" continuum or flux from ordinary hot stars. This may indicate the need for additional work on these models or it may indicate that the ionized gas in the jet/cloud interface has an energy distribution which is partly characterised by that in the radio jet plasma itself If the latter is correct, then careful measurements of these interface regions may allow us to distinguish between beams of particles composed of electrons and positrons and those composed of electrons and protons.

Abstract:

The results of a multifrequency VLA imaging study of the nearby radio galaxy 3C 31 are briefly summarized. The transition between jets and lobes is much more complex than was apparent from earlier observations, and is associated with significant variations in spectral index. We demonstrate that the known depolarization asymmetry in 3C 31 is caused by foreground Faraday rotation in the halo of the host galaxy, but the details of the associated field and density structure are not yet clear.

Abstract:

We review recent observations of circularly polarized radiation from AGN made with the VLBA and with the ATCA. We also discuss briefly the detections of the Galactic sources Sgr A* and SS 433. The origin of the circular polarization is still an open question in most cases, and we discuss four possible mechanisms. Detectable circular polarization is a common property of quasars, but not of radio galaxies, and is always associated with the compact core. There is growing evidence that the sign of the circular polarization stays the same over at least 20 - 30 years, suggesting that it is a fundamental property of the jet.

Abstract:

The observational picture for cosmic rays above 10(19) eV is described and the enigma that these results pose is discussed. The existence of particles above 10(20) eV may have an impact on our understanding of magnetic fields in intergalactic space and in possible sources.