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Sökning: WFRF:(Tchernin C.)

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1.
  • Actis, M., et al. (författare)
  • Design concepts for the Cherenkov Telescope Array CTA : an advanced facility for ground-based high-energy gamma-ray astronomy
  • 2011
  • Ingår i: Experimental astronomy. - : Springer. - 0922-6435 .- 1572-9508. ; 32:3, s. 193-316
  • Tidskriftsartikel (refereegranskat)abstract
    • Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
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2.
  • Huber, B., et al. (författare)
  • Probing the cosmic-ray content of galaxy clusters by stacking Fermi-LAT count maps
  • 2013
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 560, s. A64-
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. Radio observations have shown that galaxy clusters are giant reservoirs of cosmic rays (CR). Although a gamma-ray signal from the cluster volume is expected to arise through interactions of CR protons with the ambient plasma, a confirming observation is still missing. Methods. We searched for a cumulative gamma-ray emission in the direction of galaxy clusters by analysing a collection of stacked Fermi-LAT count maps. Additionally, we investigated possible systematic differences in the emission between cool-core and non-cool-core cluster populations. Results. Making use of a sample of 53 clusters selected from the HIFLUGCS catalog, we do not detect a significant signal from the stacked sample. The upper limit on the average flux per cluster derived for the total stacked sample is at the level of a few 10(-11) ph cm(-2) s(-1) at a 95% confidence level in the 1-300 GeV band, assuming power-law spectra with photon indices 2.0, 2.4, 2.8, and 3.2. Separate stacking of the cool-core and non-cool-core clusters in the sample lead to similar values of around 5 x 10(-11) ph cm(-2) s(-1) and 2 x 10(-11) ph cm(-2) s(-1), respectively. Conclusions. Under the assumption that decaying pi(0), produced in collisions between CRs and the ambient thermal gas, are responsible for gamma-ray emission, we set upper limits on the average CR content in galaxy clusters. For the entire cluster population, our upper limit on the gamma-ray flux translates into an upper limit on the average CR-to-thermal energy ratio of 4.6% for a photon index of 2.4, although it is possible for individual systems to exceed this limit. Our 95% upper limits are at the level expected from numerical simulations, which most likely suggests that the injection of CR at cosmological shocks is less efficient than previously assumed.
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