Cosmic Ray Feedback

Cosmic rays produced or deposited at sites in hot cluster gas are thought to provide the pressure that forms X-ray cavities. While cavities have a net cooling effect on cluster gas, young, expanding cavities drive shocks that increase the local entropy. Cavities also produce radial filaments of thermal gas and are sources of cluster cosmic rays that diffuse through cavity walls, as in Virgo where a radio lobe surrounds a radial thermal filament. Cosmic rays also make the hot gas locally buoyant, allowing large masses of low entropy gas to be transported out beyond the cooling radius. Successive cavities maintain a buoyant outflow that preserves the cluster gas temperature and gas fraction profiles and dramatically reduces the cooling rate onto the central black hole.Comment: 4 pages, 1 figure, to appear in proceedings of the conference "The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", June 2009, Madison Wisconsi

Peculiar Velocity and Deaberration of the Sky

Recent studies have found the earth's peculiar velocity to be significant in microwave background based tests for compact cosmic topology, and modifications to these tests have been proposed. Tests of non-gaussianity, weak lensing analysis and new tests using improved CMB data will also be sensitive to peculiar velocity. We propose here to simplify matters by showing how to construct a deaberrated CMB map to which any test requiring a Hubble flow viewpoint can be applied without further complication. In a similar manner deaberration can also be applied to object surveys used for example in topological searches and matter distribution analysis. In particular we have produced a revised list of objects with z > 1.0 using the NASA/IPAC Extragalactic Database.Comment: 8 pages, 1 figure, v4 accepted by Ap

Cosmic ray diffusion fronts in the Virgo cluster

The pair of large radio lobes in the Virgo cluster, each about 23 kpc in radius, have curiously sharp outer edges where the radio-synchrotron continuum flux declines abruptly. However, just adjacent to this sharp transition, the radio flux increases. This radio limb-brightening is observed over at least half of the perimeter of both lobes. We describe slowly propagating steady state diffusion fronts that explain these counterintuitive features. Because of the natural buoyancy of radio lobes, the magnetic field is largely tangent to the lobe boundary, an alignment that polarizes the radio emission and dramatically reduces the diffusion coefficient of relativistic electrons. As cosmic ray electrons diffuse slowly into the cluster gas, the local magnetic field and gas density are reduced as gas flows back toward the radio lobe. Radio emission peaks can occur because the synchrotron emissivity increases with magnetic field and then decreases with the density of non-thermal electrons. A detailed comparison of steady diffusion fronts with quantitative radio observations may reveal information about the spatial variation of magnetic fields and the diffusion coefficient of relativistic electrons. On larger scales, some reduction of the gas density inside the Virgo lobes due to cosmic ray pressure must occur and may be measurable. Such X-ray observations could reveal important information about the presence of otherwise unobservable non-thermal components such as relativistic electrons of low energy or proton cosmic rays.Comment: 11 pages, 5 figures, Accepted by Ap

Nuclear Equation of State and Internal Structure of Magnetars

Recently, neutron stars with very strong surface magnetic fields have been suggested as the site for the origin of observed soft gamma repeaters (SGRs). We investigate the influence of a strong magnetic field on the properties and internal structure of such strongly magnetized neutron stars (magnetars). The presence of a sufficiently strong magnetic field changes the ratio of protons to neutrons as well as the neutron appearance density. We also study the pion production and pion condensation in a strong magnetic field. We discuss the pion condensation in the interior of magnetars as a possible source of SGRs.Comment: 5 pages with 3 figures, To appear in the Proceedings of the 5th Huntsville Gamma Ray Burst Symposium, Huntsville, Alabama, USA, Oct. 18-22, 199

Absence of a Lower Limit on Omega_b in Inhomogeneous Primordial Nucleosynthesis

We show that a class of inhomogeneous big bang nucleosynthesis models exist which yield light-element abundances in agreement with observational constraints for baryon-to-photon ratios significantly smaller than those inferred from standard homogeneous big bang nucleosynthesis (HBBN). These inhomogeneous nucleosynthesis models are characterized by a bimodal distribution of baryons in which some regions have a local baryon-to-photon ratio eta=3*10e-10, while the remaining regions are baryon-depleted. HBBN scenarios with primordial (2H+3He)/H<9*10e-5 necessarily require that most baryons be in a dark or non-luminous form, although new observations of a possible high deuterium abundance in Lyman-alpha clouds may relax this requirement somewhat. The models described here present another way to relax this requirement and can even eliminate any lower bound on the baryon-to-photon ratio.Comment: 13 pages, 2 figures (available upon request by email), plain te