Hard X-ray emission from the galaxy cluster A2256

After the positive detection by BeppoSAX of hard X-ray radiation up to ~80 keV in the Coma cluster spectrum, we present evidence for nonthermal emission from A2256 in excess of thermal emission at a 4.6sigma confidence level. In addition to this power law component, a second nonthermal component already detected by ASCA could be present in the X-ray spectrum of the cluster, not surprisingly given the complex radio morphology of the cluster central region. The spectral index of the hard tail detected by the PDS onboard BeppoSAX is marginally consistent with that expected by the inverse Compton model. A value of ~0.05 microG is derived for the intracluster magnetic field of the extended radio emission in the northern regions of the cluster, while a higher value of \~0.5 microG could be present in the central radio halo, likely related to the hard tail detected by ASCA.Comment: 10 pages, 2 figures. To appear in ApJ

Iron Abundance Profiles of 12 Clusters of Galaxies Observed With BeppoSAX

We have derived azimuthally-averaged radial iron abundance profiles of the X-ray gas contained within 12 clusters of galaxies with redshift 0.03 < z < 0.2 observed with BeppoSAX. We find evidence for a negative metal abundance gradient in most of the clusters, particularly significant in clusters that possess cooling flows. The composite profile from the 12 clusters resembles that of cluster simulations of Metzler & Evrard (1997). This abundance gradient could be the result of the spatial distribution of gas-losing galaxies within the cluster being more centrally condensed than the primordial hot gas. Both inside and outside the core region, we find a higher abundance in cooling flow clusters than in non-cooling flow clusters. Outside of the cooling region this difference cannot be the result of more efficient sputtering of metals into the gaseous phase in cooling flow clusters, but might be the result of the mixing of low metallicity gas from the outer regions of the cluster during a merger.Comment: 8 pages, 2 embedded Postscript figures, accepted by Astrophysical Journa

Dyons in Nonabelian Born-Infeld Theory

We analyze a nonabelian extension of Born--Infeld action for the SU(2) group. In the class of spherically symmetric solutions we find that, besides the Gal'tsov--Kerner glueballs, only the analytic dyons have finite energy. The presented analytic and numerical investigation excludes the existence of pure magnetic monopoles of 't Hooft--Polyakov type.Comment: 12 pages, 3 figure

Generating the curvature perturbation with instant preheating

A new mechanism for generating the curvature perturbation at the end of inflaton has been investigated. The dominant contribution to the primordial curvature perturbation may be generated during the period of instant preheating. The mechanism converts isocurvature perturbation related to a light field into curvature perturbation, where the ``light field'' is not the inflaton field. This mechanism is important in inflationary models where kinetic energy is significant at the end of inflaton. We show how one can apply this mechanism to various brane inflationary models.Comment: 17 pages, 1 figure, To appear in JCA