374 research outputs found
The Dipole Anisotropy of Galactic Cosmic Rays
The arrival directions of Galactic cosmic rays exhibit anisotropies up to the
level of one per-mille over various angular scales. Recent observations of
TeV-PeV cosmic rays show that the dipole anisotropy has a strong energy
dependence with a phase-flip around 100 TeV. We argue that this behavior can be
well understood by the combination of various effects: the anisotropic
diffusion of cosmic rays, the presence of nearby sources, the Compton-Getting
effect from our relative motion and the reconstruction bias of ground-based
observatories.Comment: 10 pages, 4 figures, Proceedings of the 26th Extended European Cosmic
Ray Symposium 201
Opening a New Window onto the Universe with IceCube
Weakly interacting neutrinos are ideal astronomical messengers because they
travel through space without deflection by magnetic fields and, essentially,
without absorption. Their weak interaction also makes them notoriously
difficult to detect, with observation of high-energy neutrinos from distant
sources requiring kilometer-scale detectors. The IceCube project transformed a
cubic kilometer of natural Antarctic ice at the geographic South Pole into a
Cherenkov detector. It discovered a flux of cosmic neutrinos in the energy
range from 10 TeV to 10 PeV, predominantly extragalactic in origin. Their
corresponding energy density is close to that of high-energy photons detected
by gamma-ray satellites and ultra-high-energy cosmic rays observed with large
surface detectors. Neutrinos are therefore ubiquitous in the nonthermal
universe, suggesting a more significant role of protons (nuclei) relative to
electrons than previously anticipated. Thus, anticipating an essential role for
multimessenger astronomy, IceCube is planning significant upgrades of the
present instrument as well as a next-generation detector. Similar detectors are
under construction in the Mediterranean Sea and Lake Baikal.Comment: 27+7 pages, 10 figures, to appear in Progress in Particle and Nuclear
Physic
Origin of Small-Scale Anisotropies in Galactic Cosmic Rays
The arrival directions of Galactic cosmic rays (CRs) are highly isotropic.
This is expected from the presence of turbulent magnetic fields in our Galactic
environment that repeatedly scatter charged CRs during propagation. However,
various CR observatories have identified weak anisotropies of various angular
sizes and with relative intensities of up to a level of 1 part in 1,000.
Whereas large-scale anisotropies are generally predicted by standard diffusion
models, the appearance of small-scale anisotropies down to an angular size of
10 degrees is surprising. In this review, we summarise the current experimental
situation for both the large-scale and small-scale anisotropies. We address
some of the issues in comparing different experimental results and remaining
questions in interpreting the observed large-scale anisotropies. We then review
the standard diffusive picture and its difficulty in producing the small-scale
anisotropies. Having set the stage, we review the various ideas and models put
forward for explaining the small-scale anisotropies.Comment: 60 pages, 16 figures; invited review for Progress in Particle and
Nuclear Physics (PPNP
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