226 research outputs found
Ultra-High Energy Cosmic Rays and Diffuse Photon Spectrum
It is argued that if extragalactic magnetic fields are smaller than
2x10^{-12} G the flux of ultra-high energy photons of (a few)x10^{-1} eV
cm^{-2}s^{-1}sr^{-1} predicted in the top-down models of UHE CR implies similar
flux of the diffuse photons in the energy range 10^{15}-10^{17} eV, which is
close to the existing experimental limit.Comment: Talk given at XI Rencontres de Blois. 3 pages, no figure
Full sky harmonic analysis hints at large UHECR deflections
The full-sky multipole coefficients of the ultra-high energy cosmic ray
(UHECR) flux have been measured for the first time by the Pierre Auger and
Telescope Array collaborations using a joint data set with E > 10 EeV. We
calculate these harmonic coefficients in the model where UHECR are protons and
sources trace the local matter distribution, and compare our results with
observations. We find that the expected power for low multipoles (dipole and
quadrupole, in particular) is sytematically higher than in the data: the
observed flux is too isotropic. We then investigate to which degree our
predictions are influenced by UHECR deflections in the regular Galactic
magnetic field (GMF). It turns out that the UHECR power spectrum coefficients
are quite insensitive to the effects of the GMF, so it is unlikely
that the discordance can be reconciled by tuning the GMF model. On the
contrary, a sizeable fraction of uniformly distributed flux (representing for
instance an admixture of heavy nuclei with considerably larger deflections) can
bring simulations and observations to an accord.Comment: 8 pages, 4 figures and one table, JETPL style -- v2 as published in
JETP
GRB observations by Fermi LAT revisited: new candidates found
We search the Fermi-LAT photon database for an extended gamma-ray emission
which could be associated with any of the 581 previously detected gamma-ray
bursts (GRBs) visible to the Fermi-LAT. For this purpose we compare the number
of photons with energies E > 100 MeV and E > 1 GeV which arrived in the first
1500 seconds after the burst from the same region, to the expected background.
We require that the expected number of false detections does not exceed 0.05
for the entire search and find the high-energy emission in 19 bursts, four of
which (GRB 081009, GRB 090720B, GRB 100911 and GRB 100728A) were previously
unreported. The first three are detected at energies above 100 MeV, while the
last one shows a statistically significant signal only above 1 GeV.Comment: Updated after referee comments, published in MNRAS Letters; 5 pages,
2 table
Comment on "Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects"
We argue that the data published by the Pierre Auger Collaboration
(arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most
of the highest-energy cosmic rays are protons from nearby astrophysical
sources, either Active Galactic Nuclei or other objects with a similar spatial
distribution.Comment: 1000 words, 2 figures, scicite.st
Is the electric charge conserved in brane world?
We discuss whether electric charge conservation may not hold in
four-dimensional world in models with infinite extra dimensions, i.e., whether
escape of charged particles from our brane is consistent with effectively
four-dimensional electrodynamics on the brane. We introduce a setup with photon
localized on the brane and show that charge leakage into extra dimension is
allowed within this setup. The electric field induced on the brane by escaping
charge does not obey four-dimensional Maxwell's equations; this field gradually
disappears in a causal way. We also speculate on the possibility of the escape
of colored particles and formation of colorless free quark states on the brane.Comment: 14 pages, 4 figures, misprint correcte
Star Wreck
Electroweak models with low-energy supersymmetry breaking predict the
existence of stable non-topological solitons, Q-balls, that can be produced in
the early universe. The relic Q-balls can accumulate inside a neutron star and
gradually absorb the baryons into the scalar condensate. This causes a slow
reduction in the mass of the star. When the mass reaches a critical value, the
neutron star becomes unstable and explodes. The cataclysmic destruction of the
distant neutron stars may be the origin of the gamma-ray bursts.Comment: 9 pages; references adde
BL Lacertae are probable sources of the observed ultra-high energy cosmic rays
We calculate angular correlation function between ultra-high energy cosmic
rays (UHECR) observed by Yakutsk and AGASA experiments, and most powerful BL
Lacertae objects. We find significant correlations which correspond to the
probability of statistical fluctuation less than , including penatly
for selecting the subset of brightest BL Lacs. We conclude that some of BL Lacs
are sources of the observed UHECR and present a list of most probable
candidates.Comment: Replaced with the version accepted for publication in JETP Let
- âŠ