2,478 research outputs found
TeV Neutrinos from Successful and Choked Gamma-Ray Bursts
Core collapse of massive stars resulting in a relativistic fireball jet which
breaks through the stellar envelope is a widely discussed scenario for
gamma-ray burst production. For very extended or slow rotating stars, the
fireball may be unable to break through the envelope. Both penetrating and
choked jets will produce, by photo-meson interactions of accelerated protons, a
burst of neutrinos with energies in excess of 5 TeV while propagating in the
envelope. The predicted flux, from both penetrating and chocked fireballs,
should be easily detectable by planned cubic kilometer neutrino telescopes.Comment: Phys.Rev.Letters, in press, final version accepted 8/31/01 (orig.
3/17/01
War Powers: Congress, the President, and the Courts – A Model Casebook Section
This model casebook section is concerned with the constitutional law of war powers as developed by the executive and legislative branches, with a limited look at relevant statutes and federal court cases. It is intended for use in Constitutional Law I classes that cover separation of powers. It could also be used for courses in National Security Law or Foreign Relations Law, or for graduate courses in U.S. foreign policy. This is designed to be the reading for one to two classes, and it can supplement or replace standard casebook sections on war powers that are shorter and offer less detail. We plan to update this section periodically in response to feedback and events
GeV Photons from Ultra High Energy Cosmic Rays accelerated in Gamma Ray Bursts
Gamma-ray bursts are produced by the dissipation of the kinetic energy of a
highly relativistic fireball, via the formation of a collisionless shock. When
this happens, Ultra High Energy Cosmic Rays up to 10^20 eV are produced. I show
in this paper that these particles produce, via synchrotron emission as they
cross the acceleration region, photons up to 300 GeV which carry away a small,
~0.01, but non-negligible fraction of the total burst energy. I show that, when
the shock occurs with the interstellar medium, the optical depth to
photon-photon scattering, which might cause energy degradation of the photons,
is small. The burst thusly produced would be detected at Earth simultaneoulsy
with the parent gamma-ray burst, although its duration may differ significantly
from that of the lower energy photons. The expected fluences, ~10^{-5}-10^{-6}
erg/cm^2 are well within the range of planned detectors. A new explanation for
the exceptional burst GRB 940217 is discussed.Comment: Accepted for publication in The Physical Review Letters. 4 pages,
RevTeX needed, no figure
Extra galactic sources of high energy neutrinos
The main goal of the construction of large volume, high energy neutrino
telescopes is the detection of extra-Galactic neutrino sources. The existence
of such sources is implied by observations of ultra-high energy, >10^{19} eV,
cosmic-rays (UHECRs), the origin of which is a mystery. The observed UHECR flux
sets an upper bound to the extra-Galactic high energy neutrino intensity, which
implies that the detector size required to detect the signal in the energy
range of 1 TeV to 1 PeV is >=1 giga-ton, and much larger at higher energy.
Optical Cerenkov neutrino detectors, currently being constructed under ice and
water, are expected to achieve 1 giga-ton effective volume for 1 TeV to 1 PeV
neutrinos. Coherent radio Cerenkov detectors (and possibly large air-shower
detectors) will provide the >> 1 giga-ton effective volume required for
detection at ~10^{19} eV. Detection of high energy neutrinos associated with
electromagnetically identified sources will allow to identify the sources of
UHECRs, will provide a unique probe of the sources, which may allow to resolve
open questions related to the underlying physics of models describing these
powerful accelerators, and will provide information on fundamental neutrino
properties.Comment: 8 pages, 4 figures; Summary of talk presented at the Nobel Symposium
129: Neutrino Physics, Sweden 200
High Energy Neutrinos from Cosmological Gamma-Ray Burst Fireballs
Observations suggest that -ray bursts (GRBs) are produced by the
dissipation of the kinetic energy of a relativistic fireball. We show that a
large fraction, , of the fireball energy is expected to be converted
by photo-meson production to a burst of neutrinos. A km^2
neutrino detector would observe at least several tens of events per year
correlated with GRBs, and test for neutrino properties (e.g. flavor
oscillations, for which upward moving 's would be a unique signature, and
coupling to gravity) with an accuracy many orders of magnitude better than is
currently possible.Comment: Submitted to PRL (4 pages, LaTeX
High Energy Neutrinos from Astrophysical Sources: An Upper Bound
We show that cosmic-ray observations set a model-independent upper bound to
the flux of high-energy, > 10^14 eV, neutrinos produced by photo-meson (or p-p)
interactions in sources of size not much larger than the proton photo-meson (or
pp) mean-free-path. The bound applies, in particular, to neutrino production by
either AGN jets or GRBs. This upper limit is two orders of magnitude below the
flux predicted in some popular AGN jet models, but is consistent with our
predictions from GRB models. We discuss the implications of these results for
future km^2 high-energy neutrino detectors.Comment: Added discussion showing bound cannot be evaded by invoking magnetic
fields. Accepted Phys Rev
Ultra high energy neutrinos from gamma ray bursts
Protons accelerated to high energies in the relativistic shocks that generate
gamma ray bursts photoproduce pions, and then neutrinos in situ. I show that
ultra high energy neutrinos (> 10^19 eV) are produced during the burst and the
afterglow. A larger flux, also from bursts, is generated via photoproduction
off CMBR photons in flight but is not correlated with currently observable
bursts, appearing as a bright background. Adiabatic/synchrotron losses from
protons/pions/muons are negligible. Temporal and directional coincidences with
bursts detected by satellites can separate correlated neutrinos from the
background.Comment: Adiabatic/synchrotron losses from protons/pions/muons shown to be
negligible. Accepted for publication in Phys. Rev. Letters. RevTe
Maximum Likelihood Analysis of Clusters of Ultra-High Energy Cosmic Rays
We present a numerical code designed to conduct a likelihood analysis for
clusters of nucleons above 10**19 eV originating from discrete astrophysical
sources such as powerful radio galaxies, gamma-ray bursts or topological
defects. The code simulates the propagation of nucleons in a large-scale
magnetic field and constructs the likelihood of a given observed event cluster
as a function of the average time delay due to deflection in the magnetic
field, the source activity time scale, the total fluence of the source, and the
power law index of the particle injection spectrum. Other parameters such as
the coherence length and the power spectrum of the magnetic field are also
considered. We apply it to the three pairs of events above 4X10**19 eV recently
reported by the Akeno Giant Air Shower Array (AGASA) experiment, assuming that
these pairs were caused by nucleon primaries which originated from a common
source. Although current data are too sparse to fully constrain each of the
parameters considered, and/or to discriminate models of the origin of
ultra-high energy cosmic rays, several tendencies are indicated. If the
clustering suggested by AGASA is real, next generation experiments with their
increased exposure should detect more than 10 particles per source over a few
years and our method will put strong constraints on both the large-scale
magnetic field parameters and the nature of these sources.Comment: 11 latex pages, 8 postscript figures included, uses revtex.sty in
two-column format and epsf.sty. Submitted to Physical Review
Time dependent numerical model for the emission of radiation from relativistic plasma
We describe a numerical model constructed for the study of the emission of
radiation from relativistic plasma under conditions characteristic, e.g., to
gamma-ray bursts (GRB's) and active galactic nuclei (AGN's). The model solves
self consistently the kinetic equations for e^\pm and photons, describing
cyclo-synchrotron emission, direct Compton and inverse Compton scattering, pair
production and annihilation, including the evolution of high energy
electromagnetic cascades. The code allows calculations over a wide range of
particle energies, spanning more than 15 orders of magnitude in energy and time
scales. Our unique algorithm, which enables to follow the particle
distributions over a wide energy range, allows to accurately derive spectra at
high energies, >100 \TeV. We present the kinetic equations that are being
solved, detailed description of the equations describing the various physical
processes, the solution method, and several examples of numerical results.
Excellent agreement with analytical results of the synchrotron-SSC model is
found for parameter space regions in which this approximation is valid, and
several examples are presented of calculations for parameter space regions
where analytic results are not available.Comment: Minor changes; References added, discussion on observational status
added. Accepted for publication in Ap.
Gamma-Ray Bursts: The Underlying Model
A pedagogical derivation is presented of the ``fireball'' model of gamma-ray
bursts, according to which the observable effects are due to the dissipation of
the kinetic energy of a relativistically expanding wind, a ``fireball.'' The
main open questions are emphasized, and key afterglow observations, that
provide support for this model, are briefly discussed. The relativistic outflow
is, most likely, driven by the accretion of a fraction of a solar mass onto a
newly born (few) solar mass black hole. The observed radiation is produced once
the plasma has expanded to a scale much larger than that of the underlying
``engine,'' and is therefore largely independent of the details of the
progenitor, whose gravitational collapse leads to fireball formation. Several
progenitor scenarios, and the prospects for discrimination among them using
future observations, are discussed. The production in gamma- ray burst
fireballs of high energy protons and neutrinos, and the implications of burst
neutrino detection by kilometer-scale telescopes under construction, are
briefly discussed.Comment: In "Supernovae and Gamma Ray Bursters", ed. K. W. Weiler, Lecture
Notes in Physics, Springer-Verlag (in press); 26 pages, 2 figure
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