Magnetic fields in cosmic particle acceleration sources

We review here some magnetic phenomena in astrophysical particle accelerators associated with collisionless shocks in supernova remnants, radio galaxies and clusters of galaxies. A specific feature is that the accelerated particles can play an important role in magnetic field evolution in the objects. We discuss a number of CR-driven, magnetic field amplification processes that are likely to operate when diffusive shock acceleration (DSA) becomes efficient and nonlinear. The turbulent magnetic fields produced by these processes determine the maximum energies of accelerated particles and result in specific features in the observed photon radiation of the sources. Equally important, magnetic field amplification by the CR currents and pressure anisotropies may affect the shocked gas temperatures and compression, both in the shock precursor and in the downstream flow, if the shock is an efficient CR accelerator. Strong fluctuations of the magnetic field on scales above the radiation formation length in the shock vicinity result in intermittent structures observable in synchrotron emission images. Resonant and non-resonant CR streaming instabilities in the shock precursor can generate mesoscale magnetic fields with scale-sizes comparable to supernova remnants and even superbubbles. This opens the possibility that magnetic fields in the earliest galaxies were produced by the first generation Population III supernova remnants and by clustered supernovae in star forming regions.Comment: 30 pages, Space Science Review

Analysis of autoionization resonances in the Hg 6s2-photoionization by measurements of photoelectron polarization

Schäfers F, Schönhense G, Heinzmann U. Analysis of autoionization resonances in the Hg 6s2-photoionization by measurements of photoelectron polarization. Zeitschrift für Physik A: Hadrons and Nuclei. 1982;304(1):41-48.Measurements of the spin polarization of photoelectrons in the autoionization region of the Hg 6s2-subshell using circularly polarized synchrotron radiation and using unpolarized light from rare gas discharge lamps are reported. The results obtained show a pronounced structure across the resonances. Together with data of the cross section and its angular distribution these data from a complete parameter set for the determination of the transition matrix elements and the phase difference of the continuum wavefunctions. Evidences for strong configuration interaction and channel mixing between the open and closed channels were found. The matrix elements and their ratio vary strongly across the resonances and the relative phase shows some changes of sign. A change of the relative phase by Pi across an autoionization resonance, predicted by Fano, has been verified experimentally for the triplet resonance. We would like to express our gratitude to Professors W. Paul, G. Nöldeke and J. Kessler for their continued interest and encouragement. We thank Dr. D. Husmann, Dr. J. Hormes and B. Osterheld for their assistance in performing the experiment in Bonn. We are grateful to Dr. N.A. Cherepkov for helpful discussions and acknowledge support by the DFG and BMFT