614 research outputs found
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
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
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
Neutrino Fluxes from Active Galaxies: a Model-Independent Analysis
There are tantalizing hints that jets, powered by supermassive black holes at
the center of active galaxies, are true cosmic proton accelerators. They
produce photons of TeV energy, possible higher, and may be the enigmatic source
of the highest energy cosmic rays. Photoproduction of neutral pions by
accelerated protons on UV light is the source of the highest energy photons, in
which most of the bolometric luminosity of the galaxy may be emitted. The case
that proton beams power active galaxies is, however, far from conclusive.
Neutrinos from the decay of charged pions represent an uncontrovertible
signature for the proton induced cascades. We show that their flux can be
estimated by model-independent methods, based on dimensional analysis and
textbook particle physics. Our calculations also demonstrate why different
models for the proton blazar yield very similar results for the neutrino flux,
consistent with the ones obtained here.Comment: Latex 2.09 with epsf.sty. 12 pages, 2 postscript figures. Compressed
postscript version of paper with figures also available soon at
http://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-982.ps.Z or at
ftp://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-982.ps.
A physical approach to modelling large-scale galactic magnetic fields
A convenient representation of the structure of the large-scale galactic
magnetic field is required for the interpretation of polarization data in the
sub-mm and radio ranges, in both the Milky Way and external galaxies. We
develop a simple and flexible approach to construct parametrised models of the
large-scale magnetic field of the Milky Way and other disc galaxies, based on
physically justifiable models of magnetic field structure. The resulting models
are designed to be optimised against available observational data.
Representations for the large-scale magnetic fields in the flared disc and
spherical halo of a disc galaxy were obtained in the form of series expansions
whose coefficients can be calculated from observable or theoretically known
galactic properties. The functional basis for the expansions is derived as
eigenfunctions of the mean-field dynamo equation or of the vectorial magnetic
diffusion equation. The solutions presented are axially symmetric but the
approach can be extended straightforwardly to non-axisymmetric cases. The
magnetic fields are solenoidal by construction, can be helical, and are
parametrised in terms of observable properties of the host object, such as the
rotation curve and the shape of the gaseous disc. The magnetic field in the
disc can have a prescribed number of field reversals at any specified radii.
Both the disc and halo magnetic fields can separately have either dipolar or
quadrupolar symmetry. The model is implemented as a publicly available software
package GalMag which allows, in particular, the computation of the synchrotron
emission and Faraday rotation produced by the model's magnetic field. The model
can be used in interpretations of observations of magnetic fields in the Milky
Way and other spiral galaxies, in particular as a prior in Bayesian analyses.
(Abridged.)Comment: 20 pages, 14 figures. Accepted for publication in A&
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