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Clapson A.-C.,Max Planck Institute for Nuclear Physics | Domainko W.,Max Planck Institute for Nuclear Physics | Jamrozy M.,Jagiellonian University | Dyrda M.,Instytut Fizyki Jadrowej PAN | Eger P.,Friedrich - Alexander - University, Erlangen - Nuremberg
Astronomy and Astrophysics | Year: 2011

Terzan 5 is a Galactic globular cluster exhibiting prominent X-ray and gamma-ray emission. Following the discovery of extended X-ray emission in this object, we explore here archival data at several wavelengths for other unexpected emission features in the vicinity of this globular cluster. Radio data from the Effelsberg 100-m telescope show several extended structures near Terzan 5, albeit with large uncertainties in the flux estimates and no reliable radio spectral index. In particular, a radio source extending from the location of Terzan 5 to the north-west could result from long-term non-thermal electron production by the large population of milli-second pulsars in this globular cluster. Another prominent radio structure close to Terzan 5 may be explained by ionised material produced by a field O star. As for the diffuse X-ray emission found in Terzan 5, its extension appears to be limited to within 2.5 arcmin of the globular cluster and the available multi-wavelength data is compatible with an inverse Compton scenario but disfavours a non-thermal Bremsstrahlung origin. © 2011 ESO.

Domainko W.,Max Planck Institute for Nuclear Physics | Clapson A.-C.,Max Planck Institute for Nuclear Physics | Clapson A.-C.,Cell Biology and Biophysics and Developmental Biology Units | Brun F.,Ecole Polytechnique - Palaiseau | And 5 more authors.
Proceedings of the 32nd International Cosmic Ray Conference, ICRC 2011 | Year: 2011

Globular clusters are old stellar systems which exhibit very-high stellar densities in their cores. The globular cluster Terzan 5 is characterized by a high stellar encounter rate and hosts the largest detected population of millisecond pulsars. It also features bright GeV gamma-ray emission and extended X-ray radiation. However, no globular clusters have been detected in very-high-energy gamma rays (VHE, E> 100 GeV) so far. In order to investigate this possibility Terzan 5 has been observed with the H.E.S.S. telescope array in this energy band. The discovery of a source of VHE gamma rays from the direction of this globular cluster will be reported. The results of the VHE analysis and a multi-wavelength view of Terzan 5 will be presented in this contribution. No counterpart of model can fully explain the observed morphology of the detected VHE gamma-ray source.

Gargate L.,University of Lisbon | Gargate L.,Princeton University | Fonseca R.A.,University of Lisbon | Niemiec J.,Instytut Fizyki Jadrowej PAN | And 5 more authors.
Astrophysical Journal Letters | Year: 2010

A non-resonant instability for the amplification of the interstellar magnetic field in young supernova remnant (SNR) shocks was predicted by Bell, and is thought to be relevant for the acceleration of cosmic-ray (CR) particles. For this instability, the CRs streaming ahead of SNR shock fronts drive electromagnetic waves with wavelengths much shorter than the typical CR Larmor radius, by inducing a current parallel to the background magnetic field. We explore the nonlinear regime of the non-resonant mode using Particle-in-Cell hybrid simulations, with kinetic ions and fluid electrons, and analyze the saturation mechanism for realistic CR and background plasma parameters. In the linear regime, the observed growth rates and wavelengths match the theoretical predictions; the nonlinear stage of the instability shows a strong reaction of both the background plasma and the CR particles, with the saturation level of the magnetic field varying with the CR parameters. The simulations with CR-to-background density ratios of n CR/n b = 10 -5 reveal the highest magnetic field saturation levels, with energy also being transferred to the background plasma and to the perpendicular velocity components of the CR particles. The results show that amplification factors > 10 for the magnetic field can be achieved, and suggest that this instability is important for the generation of magnetic field turbulence, and for the acceleration of CR particles. © 2010. The American Astronomical Society. All rights reserved.

Wieland V.,University of Potsdam | Pohl M.,University of Potsdam | Pohl M.,German Electron Synchrotron | Niemiec J.,Instytut Fizyki Jadrowej PAN | And 2 more authors.
Astrophysical Journal | Year: 2016

For parameters that are applicable to the conditions at young supernova remnants, we present results of twodimensional, three-vector (2D3V) particle-in-cell simulations of a non-relativistic plasma shock with a large-scale perpendicular magnetic field inclined at a 45˚ angle to the simulation plane to approximate three-dimensional (3D) physics. We developed an improved clean setup that uses the collision of two plasma slabs with different densities and velocities, leading to the development of two distinctive shocks and a contact discontinuity. The shock formation is mediated by Weibel-type filamentation instabilities that generate magnetic turbulence. Cyclic reformation is observed in both shocks with similar period, for which we note global variations due to shock rippling and local variations arising from turbulent current filaments. The shock rippling occurs on spatial and temporal scales produced by the gyro-motions of shock-reflected ions. The drift motion of electrons and ions is not a gradient drift, but is commensurate with E B drift. We observe a stable supra-thermal tail in the ion spectra, but no electron acceleration because the amplitude of the Buneman modes in the shock foot is insufficient for trapping relativistic electrons. We see no evidence of turbulent reconnection. A comparison with other twodimensional (2D) simulation results suggests that the plasma beta and the ion-to-electron mass ratio are not decisive for efficient electron acceleration, but the pre-acceleration efficacy might be reduced with respect to the 2D results once 3D effects are fully accounted for. Other microphysical factors may also play a part in limiting the amplitude of the Buneman waves or preventing the return of electrons to the foot region. © 2016. The American Astronomical Society. All rights reserved.

Benetti P.,University of Pavia | Acciarri R.,University of LAquila | Belluco M.,University of Pavia | Calligarich E.,University of Pavia | And 20 more authors.
Nuclear Physics B - Proceedings Supplements | Year: 2011

A method to measure the low energy nuclear recoils induced by weakly interactive massive particles (WIMPs) has been achieved by means of an ultra pure Liquid Argon detector. The simultaneous observation of scintillation and ionization occurring in the liquid Argon allow to obtain a very high rejection power against background sources. The first preliminary upper bounds on WIMP parameters obtained with a small 2.3 liter test chamber with an accumulated fiducial exposure of about 100 kg{dot operator}day at the Gran Sasso Underground Laboratory is reported. This supports the validity of this method for a larger detector presently under construction with correspondingly increased sensitivities. © 2011.

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