On The Non Thermal Emission and Acceleration of Electrons in Coma and Other Clusters of Galaxies

Some clusters of galaxies in addition to thermal bremsstrahlung (TB), emit diffuse radiation from the intercluster medium (ICM) at radio, EUV and hard x-ray (HXR) ranges. The radio radiation is due to synchrotron by relativistic electrons, and the inverse Compton (IC) scattering by the cosmic microwave background radiation of the same electrons is the most natural source for the HXR and perhaps the EUV emissions. However, simple estimates give a weaker magnetic field than that suggested by Faraday rotation measurements. Consequently, non-thermal bremsstrahlung (NTB) and TB have also been suggested as sources of these emissions. We show that NTB cannot be the source of the HXRs and that the difficulty with the low magnetic field in the IC model is alleviated if we take into account the effects of observational bias, nonisotropic pitch angle distribution and spectral breaks. We derive a spectrum for the radiating electrons and discuss acceleration scenarios. We show that continuous and in situ acceleration in the ICM of the background thermal electrons requires unreasonably high energy input and acceleration of injected relativistic electrons gives rise to a much flatter spectrum than desired, unless a large fraction of electrons escape the ICM, in which case one obtains EUV and HXR emissions extending well beyond the boundaries of the cluster. A continuous emission by a cooling spectrum resulting from interaction with ICM of electrons accelerated elsewhere also suffers from similar shortcomings. The most likely scenario appears to be an episodic injection-acceleration model, whereby one obtains a time dependent spectrum that for certain phases of its evolution satisfies all the requirements.Comment: 27 pages, one Table, Four Figures. Latex AAS v5.0. Accepted by Ap

On the equipartition of thermal and non-thermal energy in clusters of galaxies

Clusters of galaxies are revealing themselves as powerful sources of non thermal radiation in a wide range of wavelengths. In order to account for these multifrequency observations equipartition of cosmic rays (CRs) with the thermal gas in clusters of galaxies is often invoked. This condition might suggest a dynamical role played by cosmic rays in the virialization of these large scale structures and is now testable through gamma ray observations. We show here, in the specific case of the Coma and Virgo clusters, for which upper limits on the gamma ray emission exist, that equipartition implies gamma ray fluxes that are close or even in excess of the EGRET limit, depending on the adopted model of CR injection. We use this bound to limit the validity of the equipartition condition. We also show that, contrary to what claimed in previous calculations, the equipartition assumption implies gamma ray fluxes in the TeV range which can be detectable even by currently operating gamma ray observatories if the injection cosmic ray spectrum is flatter than $E^{-2.4}$.Comment: 20 pages + 2 figures. To appear in the Astrophysical Journa

Kondo Effect in a Many-Electron Quantum Ring

The Kondo effect is investigated in a many-electron quantum ring as a function of magnetic field. For fields applied perpendicular to the plane of the ring a modulation of the Kondo effect with the Aharonov-Bohm period is observed. This effect is discussed in terms of the energy spectrum of the ring and the parametrically changing tunnel coupling. In addition, we use gate voltages to modify the ground-state spin of the ring. The observed splitting of the Kondo-related zero-bias anomaly in this configuration is tuned with an in-plane magnetic field.Comment: 4 pages, 4 figure

SZ effect from radio-galaxy lobes: astrophysical and cosmological relevance

We derive the SZ effect arising in radio-galaxy lobes that are filled with high-energy, non-thermal electrons. We provide here quantitative estimates for SZ effect expected from the radio galaxy lobes by normalizing it to the Inverse-Compton light, observed in the X-ray band, as produced by the extrapolation to low energies of the radio emitting electron spectrum in these radio lobes. We compute the spectral and spatial characteristics of the SZ effect associated to the radio lobes of two distant radio galaxies (3C294 and 3C432) recently observed by Chandra, and we further discuss its detectability with the next generation microwave and sub-mm experiments with arcsec and $\sim \mu$K sensitivity. We finally highlight the potential use of the SZE from radio-galaxy lobes in the astrophysical and cosmological context.Comment: 8 pages, 5 figures, MNRAS in pres

Singlet-Triplet Transition Tuned by Asymmetric Gate Voltages in a Quantum Ring

Wavefunction and interaction effects in the addition spectrum of a Coulomb blockaded many electron quantum ring are investigated as a function of asymmetrically applied gate voltages and magnetic field. Hartree and exchange contributions to the interaction are quantitatively evaluated at a crossing between states extended around the ring and states which are more localized in one arm of the ring. A gate tunable singlet-triplet transition of the two uppermost levels of this many electron ring is identified at zero magnetic field.Comment: 4 page