Limit shocks of relativistic magnetohydrodynamics

In this paper we show that switch-on and switch-off shocks are allowed by the shock equations of relativistic MHD and have similar properties to their Newtonian counterparts. Just like in Newtonian MHD they are limits of fast and slow shock solutions and as such they may be classified as weakly evolutionary shocks.     

Earthquakes induced by deep penetrating bombing

Introduction The phenomenon of induced seismicity is one of the most widely discussed issues in modern seismology. Many aspects of this problem, particularly remote earthquakes triggered by strong physical impacts on the lithosphere (other strong earthquakes or underground nuclear explosions) are still controversial, and need further elaboration (Console, Nikolaev, 1994). In this paper I discusses remotely triggered seismicity by using observations of seismicity with M≥5.0 (in accordance wi…     

The large-scale structure of FR-II radio sources

The large-scale flow produced by classical and relativistic jets in a uniform external medium is explored using a combination of general arguments and numerical simulations. We find that in both cases, jets with finite initial opening angles are recollimated by the high pressure in the cocoon and that the outer flow becomes approximately self-similar at large times. However, if the opening angle is significantly less than 20°, then there is an intermediate stage during which the working surface propagates at a constant speed, which is of the same order as that in the jet. The behaviour of the relativistic and classical jets is very similar, except that the relativistic jets generate lighter cocoons. Application of the model to Cygnus A gives estimates of the source age and advance speed which agree very well with spectral ageing observations. Quantitative estimates and general arguments suggest that the regularly spaced knots in the Cygnus A jet can be interpreted as shocks associated with reconfinement of an initially free jet, knot 3 of the Cygnus A jet being identified with the reflection point of the reconfinement shock. However, the model predicts too large an initial opening angle for the Cygnus A jets. It is possible that this discrepancy is due to our imposition of axisymmetry which allows the numerical jets to become much better collimated after the reconfinement than they would be in the three-dimensional case. Further study is needed to test this idea.     

Direct numerical simulations of the Blandford–Znajek effect

The time-dependent general relativistic equations of degenerate electrodynamics are solved numerically in order to study the mechanism of the electromagnetic extraction of the rotational energy of black holes. We performed a series of 2D runs for black holes with specific angular momentum, a , from 0.1 to 0.9 and for a monopole magnetic field assuming axisymmetry. In the inner region of the wind, the solution quickly settles to a steady state with an outgoing Poynting flux. In all cases the angular velocity of the magnetic field lines is almost half the angular velocity of the black hole. Thus, at least for the configuration considered, the Blandford–Znajek mechanism operates near its maximum power output.     

MHD Simulations of Crab's Jet and Torus

The Crab nebula is regarded as one of the most important “cosmic laboratories” in astrophysics, which has made a bigger impact on the development of astronomy than any other single object beyond the solar system. The most intriguing recent result is the completely unexpected discovery of a peculiar “jet-torus” structure in the inner part of the nebula. Similar structures were found later in other Crab-like nebulae. This discovery clearly indicates significant anisotropy of the wind from the Crab pulsar which has been ignored so far in simplified theoretical models of the nebula. Fortunately, the impressive progress in computational relativistic magnetohydrodynamics in recent years has made possible to study the Crab nebula without making such a drastic simplification of the problem. In this paper we present the results of the first study of such kind. They provide a likely explanation of the jet-torus pattern and show that the flow in the nebula is much more complex than it has been widely believed.     

A theoretical model of Fanaroff-Riley I jets

A fluid model of the jets in Fanaroff-Riley I class radio sources based on the idea that they are supersonic turbulent pressure confined flows consisting of relativistic and non-relativistic gases is described. Numerical simulations are used to investigate the properties of such flows propagating through typical atmospheres of an elliptical. The models whose parameters agree with the observational constraints on FR-I jets power, density, velocity, Mach number, spreading rate and pressure of relativistic particles are calculated. Natural assumptions such as a conservation of relativistic particles an equipartition of energy between magnetic field and turbulent motions are used to estimate the intensity evolution along simulated jets. It is concluded that an effective acceleration of relativistic particles is required to account for the observed FR-I jet brightness distribution.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain     

Magnetic basement: gravity‐guided magnetic source depth analysis and interpretation

We present a new integrated approach to the interpretation of magnetic basement that is based on recognition of characteristic patterns in distributions and alignments of magnetic source depth solutions above and below the surface of magnetic basement. This approach integrates a quantitative analysis of depth solutions, obtained by 2D Werner deconvolution of the magnetic data, with a qualitative evaluation of the Bouguer gravity anomalies. The crystalline/metamorphic basement and sedimentary cover have different origins, tectonic histories, lithologies and magnetic properties. These differences result in different geometries of magnetic sources associated with faults, fracture zones, igneous intrusions, erosional truncations, subcrop edges and other structural discontinuities. Properly tuned, 2D Werner deconvolution is able to resolve the intra‐sedimentary and intra‐basement magnetic source geometries into distinctly different distributions and alignments of calculated depth solutions. An empirical set of criteria, basement indicators, was developed for identification and correlation of the basement surface. The ambiguity of basement correlation with limited or non‐existent well control, which is common for onshore frontier and offshore explorations, can be reduced by incorporating the Bouguer gravity data into the process of correlation.