30 research outputs found
Supernova Neutrinos, Neutrino Oscillations, and the Mass of the Progenitor Star
We investigate the initial progenitor mass dependence of the early-phase
neutrino signal from supernovae taking neutrino oscillations into account. The
early-phase analysis has advantages in that it is not affected by the time
evolution of the density structure of the star due to shock propagation or
whether the remnant is a neutron star or a black hole. The initial mass affects
the evolution of the massive star and its presupernova structure, which is
important for two reasons when considering the neutrino signal. First, the
density profile of the mantle affects the dynamics of neutrino oscillation in
supernova. Second, the final iron core structure determines the features of the
neutrino burst, i.e., the luminosity and the average energy. We find that both
effects are rather small. This is desirable when we try to extract information
on neutrino parameters from future supernova-neutrino observations. Although
the uncertainty due to the progenitor mass is not small for intermediate
(), we
can, nevertheless, determine the character of the mass hierarchy and whether
is very large or very small.Comment: 8 pages, 15 figure
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
Relativistic Hydrodynamic Evolutions with Black Hole Excision
We present a numerical code designed to study astrophysical phenomena
involving dynamical spacetimes containing black holes in the presence of
relativistic hydrodynamic matter. We present evolutions of the collapse of a
fluid star from the onset of collapse to the settling of the resulting black
hole to a final stationary state. In order to evolve stably after the black
hole forms, we excise a region inside the hole before a singularity is
encountered. This excision region is introduced after the appearance of an
apparent horizon, but while a significant amount of matter remains outside the
hole. We test our code by evolving accurately a vacuum Schwarzschild black
hole, a relativistic Bondi accretion flow onto a black hole, Oppenheimer-Snyder
dust collapse, and the collapse of nonrotating and rotating stars. These
systems are tracked reliably for hundreds of M following excision, where M is
the mass of the black hole. We perform these tests both in axisymmetry and in
full 3+1 dimensions. We then apply our code to study the effect of the stellar
spin parameter J/M^2 on the final outcome of gravitational collapse of rapidly
rotating n = 1 polytropes. We find that a black hole forms only if J/M^2<1, in
agreement with previous simulations. When J/M^2>1, the collapsing star forms a
torus which fragments into nonaxisymmetric clumps, capable of generating
appreciable ``splash'' gravitational radiation.Comment: 17 pages, 14 figures, submitted to PR
Gravitational radiation from gamma-ray bursts as observational opportunities for LIGO and VIRGO
Gamma-ray bursts are believed to originate in core-collapse of massive stars.
This produces an active nucleus containing a rapidly rotating Kerr black hole
surrounded by a uniformly magnetized torus represented by two counter-oriented
current rings. We quantify black hole spin-interactions with the torus and
charged particles along open magnetic flux-tubes subtended by the event
horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of
frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with
GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii)
aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich
et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al.
2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating
LIGO/Virgo detectors enables searches for nearby events and their spectral
closure density 6e-9 around 250Hz in the stochastic background radiation in
gravitational waves. At current sensitivity, LIGO-Hanford may place an upper
bound around 150MSolar in GRB030329. Detection of Egw thus provides a method
for identifying Kerr black holes by calorimetry.Comment: to appear in PRD, 49
SN1987A and the properties of neutrino burst
We reanalyze the neutrino events from SN1987A in IMB and Kamiokande-II (KII)
detectors, and compare them with the expectations from simple theoretical
models of the neutrino emission. In both detectors the angular distributions
are peaked in the forward direction, and the average cosines are 2 sigma above
the expected values. Furthermore, the average energy in KII is low if compared
with the expectations; but, as we show, the assumption that a few (probably
one) events at KII have been caused by elastic scattering is not in contrast
with the 'standard' picture of the collapse and yields a more satisfactory
distributions in angle and (marginally) in energy. The observations give useful
information on the astrophysical parameters of the collapse: in our
evaluations, the mean energy of electron antineutrinos is =12-16 MeV, the
total energy radiated around (2-3)*1.E53 erg, and there is a hint for a
relatively large radiation of non-electronic neutrino species. These properties
of the neutrino burst are not in disagreement with those suggested by the
current theoretical paradigm, but the data leave wide space to non-standard
pictures, especially when neutrino oscillations are included.Comment: 14 pages, 5 figure
Anaesthetic efficacy and physiological responses to clove oil-anaesthetized kelp grouper Epinephelus bruneus
Observations on the biology of Nile tilapia, Oreochromis niloticus L., in two Ugandan crater lakes
Host Plant Records for Fruit Flies (Diptera: Tephritidae: Dacini) in the Pacific Islands: 2. Infestation Statistics on Economic Hosts
Detailed host records are listed for 39 species of Bactrocera and 2 species of Dacus fruit flies, infesting 98 species of commercial and edible fruits in the Pacific Island Countries and Territories, based on sampling and incubating in laboratory almost 13,000 field collected samples, or over 380,000 fruits. For each host-fly-country association, quantitative data are presented on the weight and number of fruits collected, the proportion of infested samples, the number of adult flies emerged per kg of fruits and, whenever available, the percentage of individual fruits infested. All the published records of each fly-host-country association are cited and erroneous or dubious published records are rectified or commented. Laboratory forced infestation data are also cited and reviewed