We present results on 12 X-ray bright clusters observed at 1.4 GHz with the Green Bank Telescope. After subtraction of point sources, we reach a median (best) 1-sigma noise level of 0.01 (0.006) microJy/sq. arcsec, and find a significant excess of di
ffuse, low surface brightness emission in 11 of 12 clusters. We present initial 1.4 GHz Very Large Array results on Abell 2319. We find: (a) four new detections tentatively classified as two halos (A2065, A2069) and two relics (A2067, A2073); (b) the first detection of the radio halo in A2061 at 1.4 GHz, making it a possible ultra-steep spectrum halo (alpha ~ 1.8); (c) a ~2 Mpc radio halo in the sloshing, minor-merger cluster A2142; (d) a >2x increase of the giant radio halo extent and luminosity in A2319; (e) a ~7x increase to the integrated radio flux and >4x increase to the observed extent of the peripheral, polarized radio relic in A1367 to ~600 kpc; (f) significant excess emission of ambiguous nature in three clusters. Our radio halo detections agree with the well-known X-ray/radio luminosity correlation, but are larger and fainter than expected. The volume averaged synchrotron emissivities are 1-2 orders of magnitude below the previous characteristic values. Some of the halo-like detections may represent previously unseen, very low surface brightness emission or blends of shock structures and sub-Mpc scale turbulent regions. Four of the five tentative halos contain one or more X-ray cold fronts, suggesting a possible connection between gas sloshing and particle acceleration on large scales. We see evidence for a possible inter-cluster filament between A2061 and A2067. For our faintest detections, we note the possibility of residual contamination from faint radio galaxies. We also quantify the sensitivity of the NVSS to extended emission as a function of angular size.[abridged]
We present a 3-dimensional analysis of the supernova remnant Cassiopeia A using high resolution spectra from the Spitzer Space Telescope. We observe supernova ejecta both immediately before and during the shock-ejecta interaction. We determine that t
he reverse shock of the remnant is spherical to within 7%, although the center of this sphere is offset from the geometric center of the remnant by 810 km/s. We determine that the velocity width of the nucleosynthetic layers is approximately 1000 km/s over 4000 square arcsecond regions, although the velocity width of a layer along any individual line of sight is <250 km/s. Si and O, which come from different nucleosynthetic layers in the progenitor star, are observed to be coincident in velocity space in some directions, but segregated by up to approximately 500 km/s in other directions. We compare these observations of the nucleosynthetic layers to predictions from supernova explosion models in an attempt to constrain such models. Finally, we observe small-scale, corrugated velocity structures that are likely caused during the supernova explosion itself, rather than hundreds of years later by dynamical instabilities at the remnants reverse shock.
For over four decades, synchrotron-radiating sources have played a series of pathfinding roles in the study of galaxy clusters and large scale structure. Such sources are uniquely sensitive to the turbulence and shock structures of large-scale enviro
nments, and their cosmic rays and magnetic fields often play important dynamic and thermodynamic roles. They provide essential complements to studies at other wavebands. Over the next decade, they will fill essential gaps in both cluster astrophysics and the cosmological growth of structure in the universe, especially where the signatures of shocks and turbulence, or even the underlying thermal plasma itself, are otherwise undetectable. Simultaneously, synchrotron studies offer a unique tool for exploring the fundamental question of the origins of cosmic magnetic fields. This work will be based on the new generation of m/cm-wave radio telescopes now in construction, as well as major advances in the sophistication of 3-D MHD simulations.
