Pulsars, transients and relativistic astrophysics

Abstract:

The presence of optical synchrotron jets in radio galaxies is relatively unusual. We show that of the nearest five FRI 3CR radio galaxies showing optical jets, four display evidence for almost circular, presumably face-on, dust discs. None of the other twenty nearby FRIs in our sample show circular dust discs, although dust is found in 19/20 cases. This is strong support for the two-fold idea that (1) jets emerge close to perpendicular to inner gas discs and (2) optical non-thermal synchrotron emission is seen only when the jet points towards the observer. The implied critical angle to the line-of-sight is approximately 30-40 degrees, i.e. if the angle of the jet to the line-of-sight is less than about 35 degrees we see an optical jet. The corresponding Lorentz factor is gamma approximate to 1.5, which is consistent with current observations of jet proper motion that show an apparent velocity range from; approximate to 0.6c to 6c for M 87 in the optical (Biretta, Sparks & Macchetto 1999). The relatively low speeds implied by the dust discs may be due to a global deceleration of the jet as in unified theories, or else to stratification within the jet. Unresolved nuclei are common in the optical. Their luminosities are also consistent with the beaming concept when compared to inclination inferred from the dust lanes. The disc sizes are typically several hundred parsecs, to kiloparsec size. The galaxy with an optical jet that does not show a face-on disc, M 87, instead has more complex radial dust and ionized gas filaments.

Abstract:

Cosmological gamma-ray bursts are probably powered by high-angular momentum black hole-torus systems, formed by black hole-neutron star coalescence or magnetized collapsars. Rapidly rotating black holes surrounded by torus magnetospheres are magnetized in their ground state. In this state, the black hole is connected to infinity by,an open flux-tube of magnetic field-lines. Differential. frame-dragging permits in-situ pair-production along these flux-tubes. HETE-II may bring our understanding of short bursts on pax with that of long bursts.

Abstract:

Different scenarios which have been proposed for the production of high energy radiation in blazars will be briefly summarized. Recent results on the energy spectral distribution of high redshift radio-loud quasars are then considered in the context of the blazar phenomenology and their consequences for our understanding of jets are discussed. Finally, a possible scenario for the origin of X-ray emission from large scale jets, as detected by Chandra, is presented.

Abstract:

In this contribution we present some interim results concerning the spectral indices of the hot-spots of high redshift radio galaxies and quasars. This work forms a part of the Distant DRAGNs Survey, a project to map at sub-kpc resolution a sample of z > 1.5 radio galaxies and quasars drawn from multiple flux-density-limited samples.

Abstract:

With particular reference to the BL Lac object, Markarian 501, we emphasize the importance of X-ray and gamma-ray observations for elucidating the parameters of parsec scale and sub-parsec.scale jets. In particular the magnetic field, particle energy density and Doppler factor can be inferred from simultaneous observations. The energy flux in the Mkn 501 jet is particle dominated. If the composition is electron-proton then the minimum electron Lorentz factor, gamma(1) similar to 100. Consideration of a sample of quasar and BL Lac jets, shows that these jets may consist of electron-positron pairs, also if gamma(1) similar to 100. Seyfert jets may be examples of jets in which the plasma composition is predominantly electron-proton, suggesting that they originate at larger radii (with respect to the gravitational radius) than jets in radio-loud galaxies.