1,138 research outputs found
Constrained Simulations of the Magnetic Field in the Local Supercluster and the Propagation of UHECR
Magnetic fields (MF) in the Local Supercluster (LSC) of galaxies may have
profound consequences for the propagation of Ultra High Energy Cosmic Rays
(UHECR). Faraday rotations measurements provide some informations about MF in
compact clusters. However, very few is known about less dense regions and about
the global structure of MF in the LSC. In order to get a better knowledge of
these fields we are performing constrained magnetohydrodynamical simulations of
the LSC magnetic field. We will present the results of our simulation and
discuss their implications for the angular distribution of expected UHECR
deflections.Comment: 4 pages + 1 figure. Published on the Proceedings of the 28th
International Cosmic Ray Conference, Tsukuba, Japan (2003
No evidence for gamma-ray halos around active galactic nuclei resulting from intergalactic magnetic fields
We analyze the gamma-ray halo around stacked AGNs reported in Ap.J.Lett.,
2010, 722, L39. First, we show that the angular distribution of gamma-rays
around the stacked AGNs is consistent with the angular distribution of the
gamma-rays around the Crab pulsar, which is a point source for Fermi/LAT. This
makes it unlikely that the halo is caused by an electromagnetic cascade of TeV
photons in the intergalactic space. We then compare the angular distribution of
gamma-rays around the stacked AGNs with the point-spread function (PSF) of
Fermi/LAT and confirm the existence of an excess above the PSF. However, we
demonstrate that the magnitude and the angular size of this effect is different
for photons converted in the front and back parts of the Fermi/LAT instrument,
and thus is an instrumental effect.Comment: accepted to A&
Estimate of the correlation signal between cosmic rays and BL Lacs in future data
The existing correlation between BL Lacertae objects (BL Lacs) and cosmic-ray
events observed by HiRes experiment provide sufficient information to formulate
quantitatively the hypothesis about the flux of neutral cosmic-ray particles
originated from BL Lacs. We determine the potential of future cosmic ray
experiments to test this hypothesis by predicting the number of coincidences
between arrival directions of cosmic rays and positions of BL Lacs on the
celestial sphere, which should be observed in the future datasets. We find that
the early Pierre Auger data will not have enough events to address this
question. On the contrary, the final Pierre Auger data and the early Telescope
Array data will be sufficient to fully test this hypothesis. If confirmed, it
would imply the existence of highest-energy neutral particles coming from
cosmological distances.Comment: 5 page
Photons as Ultra High Energy Cosmic Rays ?
We study spectra of the Ultra High Energy Cosmic Rays assuming primaries are
protons and photons, and that their sources are extragalactic. We assume power
low for the injection spectra and take into account the influence of cosmic
microwave, infrared, optical and radio backgrounds as well as extragalactic
magnetic fields on propagation of primaries. Our additional free parameters are
the maximum energy of injected particles and the distance to the nearest
source. We find a parameter range where the Greisen-Zatsepin-Kuzmin cut-off is
avoided.Comment: 4 pages, 4 figure
Quantum Dew
We consider phase separation in nonequilibrium Bose gas with an attractive
interaction between the particles. Using numerical integrations on a lattice,
we show that the system evolves into a state that contains drops of
Bose-Einstein condensate suspended in uncondensed gas. When the initial gas is
sufficiently rarefied, the rate of formation of this quantum dew scales with
the initial density as expected for a process governed by two-particle
collisions.Comment: 4 pages, revtex, 5 figure
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