14 research outputs found
Cosmic infrared background excess from axion-like particles and implications for multi-messenger observations of blazars
The first measurement of the diffuse background spectrum at 0.8-1.7 from the CIBER experiment has revealed a significant excess of the
cosmic infrared background (CIB) radiation compared to the theoretically
expected spectrum. We revisit the hypothesis that decays of axionlike particle
(ALP) can explain this excess, extending previous analyses to the case of a
warm relic population. We show that such a scenario is not excluded by
anisotropy measurements nor by stellar cooling arguments. Moreover, we find
that the increased extragalactic background light (EBL) does not contradict
observations of blazar spectra. Furthermore, the increased EBL attenuates the
diffuse TeV gamma-ray flux and alleviates the tension between the detected
neutrino and gamma ray fluxes.Comment: 11 pages, 5 figures. Several changes to match published versio
Ultra-High Energy Cosmic Rays and the GeV-TeV Diffuse Gamma-Ray Flux
Ultra-high energy cosmic ray protons accelerated in astrophysical objects
produce secondary electromagnetic cascades during propagation in the cosmic
microwave and infrared backgrounds. We show that such cascades can contribute
between ~1% and ~50% of the GeV-TeV diffuse photon flux measured by the EGRET
experiment. The GLAST satellite should have a good chance to discover this
flux.Comment: 4 pages, 5 figure
Prospects for future very high-energy gamma-ray sky survey: impact of secondary gamma rays
Very high-energy gamma-ray measurements of distant blazars can be well
explained by secondary gamma rays emitted by cascades induced by
ultra-high-energy cosmic rays. The secondary gamma rays will enable one to
detect a large number of blazars with future ground based gamma-ray telescopes
such as Cherenkov Telescope Array (CTA). We show that the secondary emission
process will allow CTA to detect 100, 130, 150, 87, and 8 blazars above 30 GeV,
100 GeV, 300 GeV, 1 TeV, and 10 TeV, respectively, up to assuming the
intergalactic magnetic field (IGMF) strength G and an unbiased all
sky survey with 0.5 hr exposure at each Field of View, where total observing
time is hr. These numbers will be 79, 96, 110, 63, and 6 up to
in the case of G. This large statistics of sources will
be a clear evidence of the secondary gamma-ray scenarios and a new key to
studying the IGMF statistically. We also find that a wider and shallower survey
is favored to detect more and higher redshift sources even if we take into
account secondary gamma rays.Comment: 8 pages, 3 figures, accepted for publication in Astroparticle Physic
GZK Photons Above 10 EeV
We calculate the flux of "GZK-photons", namely the flux of photons produced
by extragalactic nucleons through the resonant photoproduction of pions, the so
called GZK effect. This flux depends on the UHECR spectrum on Earth, of the
spectrum of nucleons emitted at the sources, which we characterize by its slope
and maximum energy, on the distribution of sources and on the intervening
cosmological backgrounds, in particular the magnetic field and radio
backgrounds. For the first time we calculate the GZK photons produced by
nuclei. We calculate the possible range of the GZK photon fraction of the total
UHECR flux for the AGASA and the HiRes spectra. We find that for nucleons
produced at the sources it could be as large as a few % and as low as 10^{-4}
above 10 EeV. For nuclei produced at the sources the maximum photon fraction is
a factor of 2 to 3 times smaller above 10 EeV but the minimum could be much
smaller than for nucleons. We also comment on cosmogenic neutrino fluxes.Comment: 20 pages, 9 figures (21 panels), iopart.cls and iopart12.clo needed
to typese
Composition of UHECR and the Pierre Auger Observatory Spectrum
We fit the recently published Pierre Auger ultra-high energy cosmic ray
spectrum assuming that either nucleons or nuclei are emitted at the sources. We
consider the simplified cases of pure proton, or pure oxygen, or pure iron
injection. We perform an exhaustive scan in the source evolution factor, the
spectral index, the maximum energy of the source spectrum Z E_{max}, and the
minimum distance to the sources. We show that the Pierre Auger spectrum agrees
with any of the source compositions we assumed. For iron, in particular, there
are two distinct solutions with high and low E_{max} (e.g. 6.4 10^{20} eV and 2
10^{19} eV) respectively which could be distinguished by either a large
fraction or the near absence of proton primaries at the highest energies. We
raise the possibility that an iron dominated injected flux may be in line with
the latest composition measurement from the Pierre Auger Observatory where a
hint of heavy element dominance is seen.Comment: 19 pages, 6 figures (33 panels)- Uses iopart.cls and iopart12.clo- In
version 2: addition of a few sentences and two reference
Ultra-High Energy Neutrino Fluxes and Their Constraints
Applying our recently developed propagation code we review extragalactic
neutrino fluxes above 10^{14} eV in various scenarios and how they are
constrained by current data. We specifically identify scenarios in which the
cosmogenic neutrino flux, produced by pion production of ultra high energy
cosmic rays outside their sources, is considerably higher than the
"Waxman-Bahcall bound". This is easy to achieve for sources with hard injection
spectra and luminosities that were higher in the past. Such fluxes would
significantly increase the chances to detect ultra-high energy neutrinos with
experiments currently under construction or in the proposal stage.Comment: 11 pages, 15 figures, version published in Phys.Rev.
Ultra-High Energy Cosmic Rays from Neutrino Emitting Acceleration Sources?
We demonstrate by numerical flux calculations that neutrino beams producing
the observed highest energy cosmic rays by weak interactions with the relic
neutrino background require a non-uniform distribution of sources. Such sources
have to accelerate protons at least up to 10^{23} eV, have to be opaque to
their primary protons, and should emit the secondary photons unavoidably
produced together with the neutrinos only in the sub-MeV region to avoid
conflict with the diffuse gamma-ray background measured by the EGRET
experiment. Even if such a source class exists, the resulting large
uncertainties in the parameters involved in this scenario does currently not
allow to extract any meaningful information on absolute neutrino masses.Comment: 6 pages, 4 figures, RevTeX styl