400 research outputs found
Constraints on top-down models for the origin of UHECRs from the Pierre Auger Observatory data
Taking into account the Pierre Auger Observatory limits on the photon
fraction among the highest energy cosmic rays, we show that the models based on
the decay of super-heavy dark matter in the halo of our Galaxy are essentially
excluded from being the sources of UHECRs unless their contribution becomes
significant only above 100 EeV. Some top-down models based on topological
defects are however compatible with the current data and may be best
constrained in the future by the high-energy neutrino flux limit.Comment: Contribution to the 30th International Cosmic Ray Conference, Merida,
Mexico, July 200
Galactic and extragalactic contributions to the astrophysical muon neutrino signal
Spectral and anisotropy properties of IceCube astrophysical neutrino signal
reveal an evidence for a significant Galactic contribution to the neutrino flux
in Southern hemisphere. We check if the Galactic contribution is detectable in
the astrophysical muon neutrino flux observed from a low positive declinations
region of the Northern sky. Estimating the Galactic neutrino flux in this part
of the sky from gamma-ray and Southern sky neutrino data, we find that the
Northern sky astrophysical muon neutrino signal shows an excess over the
Galactic flux. This points to the presence of an additional hard spectrum
(extragalactic or large scale Galactic halo) component of astrophysical
neutrino flux. We show that the Galactic flux component should still be
detectable in the muon neutrino data in a decade long IceCube exposure.Comment: 4 pages, 3 figure
Galactic sources of E>100 GeV gamma-rays seen by Fermi telescope
We perform a search for sources of gamma-rays with energies E>100 GeV at low
Galactic latitudes |b|<10 deg using the data of Fermi telescope. To separate
compact gamma-ray sources from the diffuse emission from the Galaxy, we use the
Minimal Spanning Tree method with threshold of 5 events in inner Galaxy
(Galactic longitude |l|<60 deg) and of 3 events in outer Galaxy. Using this
method, we identify 22 clusters of very-high-energy (VHE) gamma-rays, which we
consider as "source candidates". 3 out of 22 event clusters are expected to be
produced in result of random coincidences of arrival directions of diffuse
background photons. To distinguish clusters of VHE events produced by real
sources from the background we perform likelihood analysis on each source
candidate. We present a list of 19 higher significance sources for which the
likelihood analysis in the energy band E>100 GeV gives Test Statistics (TS)
values above 25. Only 10 out of the 19 high-significance sources can be readily
identified with previously known VHE gamma-ray sources. 4 sources could be
parts of extended emission from known VHE gamma-ray sources. Five sources are
new detections in the VHE band. Among these new detections we tentatively
identify one source as a possible extragalactic source PMN J1603-4904 (a blazar
candidate), one as a pulsar wind nebula around PSR J1828-1007. High
significance cluster of VHE events is also found at the position of a source
coincident with the Eta Carinae nebula. In the Galactic Center region, strong
VHE gamma-ray signal is detected from Sgr C molecular cloud, but not from the
Galactic Center itself.Comment: 6 pages, 2 figure
Evidence for the Galactic contribution to the IceCube astrophysical neutrino flux
We show that the Galactic latitude distribution of IceCube astrophysical
neutrino events with energies above 100~TeV is inconsistent with the isotropic
model of the astrophysical neutrino flux. Namely, the Galactic latitude
distribution of the events shows an excess at low latitudes |b|<10 degrees and
a deficit at high Galactic latitude |b|> 50 degrees. We use Monte-Carlo
simulations to show that the inconsistency of the isotropic signal model with
the data is at > 3 sigma level, after the account of trial factors related to
the choice of the low-energy threshold and Galactic latitude binning in our
analysis.Comment: 4 pages, 2 figures, accepted to Astroparticle Physic
Anisotropic Cosmic Ray Diffusion and its Implications for Gamma-Ray Astronomy
Analyses of TeV-PeV cosmic ray (CR) diffusion around their sources usually
assume either isotropic diffusion or anisotropic diffusion due to the regular
Galactic magnetic field. We show that none of them are adequate on distances
smaller than the maximal scale Lmax ~ 100 pc of fluctuations in the turbulent
interstellar magnetic field. As a result, we predict anisotropic gamma-ray
emissions around CR proton and electron sources, even for uniform densities of
target gas. The centers of extended emission regions may have non-negligible
offsets from their sources, leading to risks of misidentification. Gamma-rays
from CR filaments have steeper energy spectra than those from surrounding
regions. We point out that gamma-ray telescopes can be used in the future as a
new way to probe and deduce the parameters of the interstellar magnetic field.Comment: 13 pages (2 columns), 9 figures. Published in Physical Review
Imprint of a 2 Myr old source on the cosmic ray anisotropy
We study numerically the anisotropy of the cosmic ray (CR) flux emitted by a
single source calculating the trajectories of individual CRs. We show that the
contribution of a single source to the observed anisotropy is instead
determined solely by the fraction the source contributes to the total CR
intensity, its age and its distance,and does not depend on the CR energy at
late times. Therefore the observation of a constant dipole anisotropy indicates
that a single source dominates the CR flux in the corresponding energy range. A
natural explanation for the plateau between 2--20 TeV observed in the CR
anisotropy is thus the presence of a single, nearby source. For the source age
of 2 Myr, as suggested by the explanation of the antiproton and positron data
from PAMELA and AMS-02 through a local source [arXiv:astro-ph/1504.06472], we
determine the source distance as pc. Combined with the contribution
of the global CR sea calculated in the escape model, we can explain
qualitatively the data for the dipole anisotropy. Our results suggest that the
assumption of a smooth CR source distribution should be abandoned between 200
GeV and 1 PeV.Comment: 4 pages, 4 eps figures; v2: minor changes, to appear in ApJ
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