Restrictions on the injection energy of positrons annihilating near the Galactic center

Topic: An INTEGRAL View of Compact ObjectsBeacom and Yüksel (2006) suggested an elegant method to estimate an initial energy of annihilating positrons from the ratio of 511 keV line and in-flight annihilation fluxes. The idea was that in the case of stationary injection of positrons at high energies the fluxes of 511 keV line emission (generated by thermalized positrons) and of in-flight annihilation (produced by fast positrons) were proportional to each other. For the delta-function injection spectrum they showed that the initial energy of annihilating positrons cannot exceed 3 MeV. Otherwise the expected in-flight annihilation flux of fast positrons in the range 1 to 10 MeV is higher than observed by COMPTEL. However, the conclusion may be changed significantly if one analyzes the spatial distribution of the 511 keV emission and 1-10 MeV emission. In addition if the magnetic field in Galactic center region is 1 mG or higher the injection energy of positrons produced by central compact source can be unrestricted.published_or_final_versio

Multi-wavelength Emission from the Fermi Bubble. II. Secondary Electrons and the Hadronic Model of the Bubble

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Origin of thermal and non-thermal hard X-ray emission from the Galactic center

Topic: An INTEGRAL View of Compact ObjectsWe analyse new results of CHANDRA and SUZAKU which found a flux of hard X-ray emission from the compact region around Sgr A* (r∼ 100 pc). We propose that this emission is a consequence of a special transient accretion process when a part of captured star obtains an additional angular momentum. As a result a flux of subrelativistic protons is ejected from the Galactic black hole, which heats up the background plasma in the Galactic center up to temperature about 6-10 keV and produces by inverse bremsstrahlung a flux of non-thermal X-ray emission in the energy range above 10 keV.published_or_final_versio

Diffuse Gamma Rays: Galactic and Extragalactic Diffuse Emission

"Diffuse" gamma rays consist of several components: truly diffuse emission from the interstellar medium, the extragalactic background, whose origin is not firmly established yet, and the contribution from unresolved and faint Galactic point sources. One approach to unravel these components is to study the diffuse emission from the interstellar medium, which traces the interactions of high energy particles with interstellar gas and radiation fields. Because of its origin such emission is potentially able to reveal much about the sources and propagation of cosmic rays. The extragalactic background, if reliably determined, can be used in cosmological and blazar studies. Studying the derived "average" spectrum of faint Galactic sources may be able to give a clue to the nature of the emitting objects.Comment: 32 pages, 28 figures, kapproc.cls. Chapter to the book "Cosmic Gamma-Ray Sources," to be published by Kluwer ASSL Series, Edited by K. S. Cheng and G. E. Romero. More details can be found at http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm

Clusters of galaxies : observational properties of the diffuse radio emission

Clusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures...(abridged)... Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission. The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolutionary stage, and are crucial for a comprehensive physical description of the intracluster medium. They play an important role in the cluster formation and evolution. We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos. We discuss their classification and properties. We report published results up to date and obtain and discuss statistical properties. We present the properties of large-scale magnetic fields in clusters and in even larger structures: filaments connecting galaxy clusters. We summarize the current models of the origin of these cluster components, and outline the improvements that are expected in this area from future developments thanks to the new generation of radio telescopes.Comment: Accepted for the publication in The Astronomy and Astrophysics Review. 58 pages, 26 figure