Magnetic Fields, Relativistic Particles, and Shock Waves in Cluster Outskirts

It is only now, with low-frequency radio telescopes, long exposures with high-resolution X-ray satellites and gamma-ray telescopes, that we are beginning to learn about the physics in the periphery of galaxy clusters. In the coming years, Sunyaev-Zeldovich telescopes are going to deliver further great insights into the plasma physics of these special regions in the Universe. The last years have already shown tremendous progress with detections of shocks, estimates of magnetic field strengths and constraints on the particle acceleration efficiency. X-ray observations have revealed shock fronts in cluster outskirts which have allowed inferences about the microphysical structure of shocks fronts in such extreme environments. The best indications for magnetic fields and relativistic particles in cluster outskirts come from observations of so-called radio relics, which are megaparsec-sized regions of radio emission from the edges of galaxy clusters. As these are difficult to detect due to their low surface brightness, only few of these objects are known. But they have provided unprecedented evidence for the acceleration of relativistic particles at shock fronts and the existence of muG strength fields as far out as the virial radius of clusters. In this review we summarise the observational and theoretical state of our knowledge of magnetic fields, relativistic particles and shocks in cluster outskirts.Comment: 34 pages, to be published in Space Science Review

Ultra-High Energy Cosmic Ray Probes of Large Scale Structure and Magnetic Fields

We study signatures of a structured universe in the multi-pole moments, auto-correlation function, and cluster statistics of ultra-high energy cosmic rays above 10^19 eV. We compare scenarios where the sources are distributed homogeneously or according to the baryon density distribution obtained from a cosmological large scale structure simulation. The influence of extragalactic magnetic fields is studied by comparing the case of negligible fields with fields expected to be produced along large scale shocks with a maximal strength consistent with observations. We confirm that strongly magnetized observers would predict considerable anisotropy on large scales, which is already in conflict with current data. In the best fit scenario only the sources are strongly magnetized, although deflection can still be considerable, of order 20 degrees up to 10^20 eV, and a pronounced GZK cutoff is predicted. We then discuss signatures for future large scale full-sky detectors such as the Pierre Auger and EUSO projects. Auto-correlations are sensitive to the source density only if magnetic fields do not significantly affect propagation. In contrast, for a weakly magnetized observer, degree scale auto-correlations below a certain level indicate magnetized discrete sources. It may be difficult even for next generation experiments to distinguish between structured and unstructured source distributions.Comment: 17 revtex pages, 29 ps figures, published version with minor changes, see http://link.aps.org/abstract/PRD/v70/e04300

Properties of Borachak seam coal and their deterioration on storage in open stack

A feasibility study on the low temperature carbonisation potentiality of the weakly caking high volatile Borachak seam coal being produced in Borachak Incline of the Chinakuri colliery (M/s. Bengal Coal Co. Ltd.) was undertaken at CFRI. In this context, an assessment was made of in situ physical/chemical properties of the full thickness of the seam (Pl-1) from that area. the Study also included detailed tests on the pattern of variaton of coal properties on weathering particularly in respect of caking property, swelling index, LTC tar yields, gas yields etc. (Figs. 1, 2 etc.) for the periodically drawn samples from 75-25 mm coal stack (500 tonnes) and minus 25 mm coal stack (60 tonnes) prepared at the colliery site