655 research outputs found
Ultrahigh-Energy Photons as a Probe of Nearby Transient Ultrahigh-Energy Cosmic-Ray Sources and Possible Lorentz-Invariance Violation
Detecting neutrinos and photons is crucial to identifying the sources of
ultrahigh-energy cosmic rays (UHECRs), especially for transient sources. We
focus on ultrahigh-energy gamma-ray emission from transient sources such as
gamma-ray bursts, since >EeV gamma rays can be more direct evidence of UHECRs
than PeV neutrinos and GeV-TeV gamma rays. We demonstrate that coincident
detections of about 1-100 events can be expected by current and future UHECR
detectors such as Auger and JEM-EUSO, and the detection probability can be
higher than that of neutrinos for nearby transient sources at <50-100 Mpc. They
may be useful for constraining the uncertain cosmic radio background as well as
knowing the source properties and maximum energy of UHECRs. They can also give
us more than 10^4 times stronger limits on the Lorentz-invariance violation
than current constraints.Comment: 4 pages, 3 figures, replaced to match the published version (PRL,
103, 081102
Prompt high-energy neutrinos from gamma-ray bursts in photospheric and synchrotron self-Compton scenarios
We investigate neutrino emission from gamma-ray bursts (GRBs) under
alternative scenarios for prompt emission (the photospheric and synchrotron
self-Compton scenarios) rather than the classical optically thin synchrotron
scenario. In the former scenario, we find that neutrinos from the pp reaction
can be very important at energies around 10-100 TeV. They may be detected by
IceCube/KM3Net and useful as a probe of baryon acceleration around/below the
photosphere. In the latter scenario, we may expect about EeV pgamma neutrinos
produced by soft photons. Predicted spectra are different from that in the
classical scenario, and neutrinos would be useful as one of the clues to the
nature of GRBs (the jet composition, emission radius, magnetic field and so
on).Comment: 5 pages, 3 figures, replaced to match the final version published as
PRD Rapid Communication, 78, 101302. Minor typos fixe
On photohadronic processes in astrophysical environments
We discuss the first applications of our newly developed Monte Carlo event
generator SOPHIA to multiparticle photoproduction of relativistic protons with
thermal and power law radiation fields. The measured total cross section is
reproduced in terms of excitation and decay of baryon resonances, direct pion
production, diffractive scattering, and non-diffractive multiparticle
production. Non--diffractive multiparticle production is described using a
string fragmentation model. We demonstrate that the widely used
`--approximation' for the photoproduction cross section is reasonable
only for a restricted set of astrophysical applications. The relevance of this
result for cosmic ray propagation through the microwave background and hadronic
models of active galactic nuclei and gamma-ray bursts is briefly discussed.Comment: 9 pages including 4 embedded figures, submitted to PAS
Monte-Carlo simulations of photohadronic processes in astrophysics
A new Monte Carlo program for photohadronic interactions of relativistic
nucleons with an ambient photon radiation field is presented. The event
generator is designed to fulfil typical astrophysical requirements, but can
also be used for radiation and background studies at high energy colliders such
as LEP2 and HERA, as well as for simulations of photon induced air showers.
We consider the full photopion production cross section from the pion
production threshold up to high energies.
It includes resonance excitation and decay, direct single pion production and
diffractive and non-diffractive multiparticle production.
The cross section of each individual process is calculated by fitting
experimental data, while the kinematics is determined by the underlying
particle production process. We demonstrate that our model is capable of
reproducing known accelerator data over a wide energy range.Comment: 39 pages, 17 figures, submitted to Comp.Phys.Co
Very-High-Energy Gamma-Ray Signal from Nuclear Photodisintegration as a Probe of Extragalactic Sources of Ultrahigh-Energy Nuclei
It is crucial to identify the ultrahigh-energy cosmic-ray (UHECR) sources and
probe their unknown properties. Recent results from the Pierre Auger
Observatory favor a heavy nuclear composition for the UHECRs. Under the
requirement that heavy nuclei survive in these sources, using gamma-ray bursts
as an example, we predict a diagnostic gamma-ray signal, unique to nuclei - the
emission of de-excitation gamma rays following photodisintegration. These gamma
rays, boosted from MeV to TeV-PeV energies, may be detectable by gamma-ray
telescopes such as VERITAS, HESS, and MAGIC, and especially the next-generation
CTA and AGIS. They are a promising messenger to identify and study individual
UHE nuclei accelerators.Comment: 7 pages, 4 figures, accepted for publication in PRD, with extended
descriptions. Conclusions unchange
On the role of galactic magnetic halo in the ultra high energy cosmic rays propagation
The study of propagation of Ultra High Energy Cosmic Rays (UHECR) is a key
step in order to unveil the secret of their origin. Up to now it was considered
only the influence of the galactic and the extragalactic magnetic fields. In
this article we focus our analysis on the influence of the magnetic field of
the galaxies standing between possible UHECR sources and us. Our main approach
is to start from the well known galaxy distribution up to 120 Mpc. We use the
most complete galaxy catalog: the LEDA catalog. Inside a sphere of 120 Mpc
around us, we extract 60130 galaxies with known position. In our simulations we
assign a Halo Dipole magnetic Field (HDF) to each galaxy. The code developed is
able to retro-propagate a charged particle from the arrival points of UHECR
data across our galaxies sample. We present simulations in case of Virgo
cluster and show that there is a non negligible deviation in the case of
protons of eV, even if the value is conservative. Then
special attention is devoted to the AGASA triplet where we find that NGC3998
and NGC3992 could be possible candidates as sources.Comment: Version accepted from ApJ, 5 figure
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