416 research outputs found
Neutrinos From Individual Gamma-Ray Bursts in the BATSE Catalog
We calculate the neutrino emission from individual gamma-ray bursts observed
by the BATSE detector on the Compton Gamma-Ray Observatory. Neutrinos are
produced by photoproduction of pions when protons interact with photons in the
region where the kinetic energy of the relativistic fireball is dissipated
allowing the acceleration of electrons and protons. We also consider models
where neutrinos are predominantly produced on the radiation surrounding the
newly formed black hole. From the observed redshift and photon flux of each
individual burst, we compute the neutrino flux in a variety of models based on
the assumption that equal kinetic energy is dissipated into electrons and
protons. Where not measured, the redshift is estimated by other methods. Unlike
previous calculations of the universal diffuse neutrino flux produced by all
gamma-ray bursts, the individual fluxes (compiled at
http://www.arcetri.astro.it/~dafne/grb/) can be directly compared with
coincident observations by the AMANDA telescope at the South Pole. Because of
its large statistics, our predictions are likely to be representative for
future observations with larger neutrino telescopes.Comment: 49 pages, 7 figures. Accepted for publication in Astroparticle
Physic
Neutrinos from Gamma-Ray Bursts in Pulsar Wind Bubbles: \sim 10^{16} eV
The supranova model for Gamma-Ray Bursts (GRBs) is becoming increasingly more
popular. In this scenario the GRB occurs weeks to years after a supernova
explosion, and is located inside a pulsar wind bubble (PWB). Protons
accelerated in the internal shocks that emit the GRB may interact with the
external PWB photons producing pions which decay into \sim 10^{16} eV
neutrinos. A km^2 neutrino detector would observe several events per year
correlated with the GRBs.Comment: Accepted for publication in PRL. 4 pages, 3 figures, minor change
Do long-duration GRBs follow star formation?
We compare the luminosity function and rate inferred from the BATSE long
bursts peak flux distribution with those inferred from the Swift peak flux
distribution. We find that both the BATSE and the Swift peak fluxes can be
fitted by the same luminosity function and the two samples are compatible with
a population that follows the star formation rate. The estimated local long GRB
rate (without beaming corrections) varies by a factor of five from 0.05
Gpc^(-3)yr^(-1) for a rate function that has a large fraction of high redshift
bursts to 0.27 Gpc^(-3)yr^(-1) for a rate function that has many local ones. We
then turn to compare the BeppoSax/HETE2 and the Swift observed redshift
distributions and compare them with the predictions of the luminosity function
found. We find that the discrepancy between the BeppoSax/HETE2 and Swift
observed redshift distributions is only partially explained by the different
thresholds of the detectors and it may indicate strong selection effects. After
trying different forms of the star formation rate (SFR) we find that the
observed Swift redshift distribution, with more observed high redshift bursts
than expected, is inconsistent with a GRB rate that simply follows current
models for the SFR. We show that this can be explained by GRB evolution beyond
the SFR (more high redshift bursts). Alternatively this can also arise if the
luminosity function evolves and earlier bursts were more luminous or if strong
selection effects affect the redshift determination.Comment: 15 pages, 8 figures, accepted for publication in JCA
Efficiency and spectrum of internal gamma-ray burst shocks
We present an analysis of the Internal Shock Model of GRBs, where gamma-rays
are produced by internal shocks within a relativistic wind. We show that
observed GRB characteristics impose stringent constraints on wind and source
parameters. We find that a significant fraction, of order 20 %, of the wind
kinetic energy can be converted to radiation, provided the distribution of
Lorentz factors within the wind has a large variance and provided the minimum
Lorentz factor is higher than 10^(2.5)L_(52)^(2/9), where L=10^(52)L_(52)erg/s
is the wind luminosity. For a high, >10 %, efficiency wind, spectral energy
breaks in the 0.1 to 1 MeV range are obtained for sources with dynamical time
R/c < 1 ms, suggesting a possible explanation for the observed clustering of
spectral break energies in this range. The lower limit to wind Lorenz factor
and the upper limit, around (R/10^7 cm)^(-5/6) MeV to observed break energies
are set by Thomson optical depth due to electron positron pairs produced by
synchrotron photons. Natural consequences of the model are absence of bursts
with peak emission energy significantly exceeding 1 MeV, and existence of low
luminosity bursts with low, 1 keV to 10 keV, break energies.Comment: 10 pages, 5 ps-figures. Expanded discussion of magnetic field and
electron energy fraction. Accepted for publication in Astrophysical Journa
New Physics Effects From B Meson Decays
In this talk, we point out some of the present and future possible signatures
of physics beyond the Standard Model from B-meson decays, taking R-parity
conserving and violating supersymmetry as illustrative examples.Comment: Talk given at the Sixth Workshop on High Energy Particle
Phenomenology (WHEPP-6), Chennai (Madras), India. Includes 2 epsf figure
On the detectability of gravitational waves background produced by gamma ray bursts
In this paper we discuss a new strategy for the detection of gravitational
radiation likely emitted by cosmological gamma ray burst. Robust and
conservative estimates lead to the conclusion that the uncorrelated
superimposition of bursts of gravitational waves can be detected by
interferometric detectors like VIRGO or LIGO. The expected signal is predicted
to carry two very distinctive signatures: the cosmological dipole anisotropy
and a characteristic time scale in the auto correlation spectrum, which might
be exploited, perhaps with ad hoc modifications and/or upgrading of the planned
experiments, to confirm the non-instrumental origin of the signal.Comment: 9 pages, 2 figures, LATEX2e, Accepted for pubblications as a Letter
to the Editor in Journal of Physics G: Nuclear and Particle Physic
Neutrino Induced Upward Going Muons from a Gamma Ray Burst in a Neutrino Telescope of Km^2 Area
The number of neutrino induced upward going muons from a single Gamma Ray
Burst (GRB) expected to be detected by the proposed kilometer scale IceCube
detector at the South Pole location has been calculated. The effects of the
Lorentz factor, total energy of the GRB emitted in neutrinos and its distance
from the observer (red shift) on the number of neutrino events from the GRB
have been examined. The present investigation reveals that there is possibility
of exploring the early Universe with the proposed kilometer scale IceCube
neutrino telescope.Comment: 18pages, 5 figures. Physical Review D in pres
A redshift - observation-time relation for gamma-ray bursts: evidence of a distinct sub-luminous population
We show how the redshift and peak-flux distributions of gamma-ray bursts
(GRBs) have an observation time dependence that can be used to discriminate
between different burst populations. We demonstrate how observation time
relations can be derived from the standard integral distributions and that they
can differentiate between GRB populations detected by both the BATSE and
\emph{Swift} satellites. Using \emph{Swift} data we show that a
redshift--observation-time relation (log\,\,--\,log\,) is consistent with
both a peak-flux\,--\,observation time relation (log\,\,--\,log\,) and a
standard log\,\,--\,log\, brightness distribution. As the method depends
only on rarer small- events, it is invariant to high- selection effects.
We use the log\,\,--\,log\, relation to show that sub-luminous GRBs are a
distinct population occurring at a higher rate of order . Our analysis suggests that GRB 060505 -- a
relatively nearby GRB observed without any associated supernova -- is
consistent with a sub-luminous population of bursts. Finally, we suggest that
our relations can be used as a consistency test for some of the proposed GRB
spectral energy correlations.Comment: Accepted by MNRA
Color suppressed contributions to the decay modes B_{d,s} -> D_{s,d} D_{s,d}, B_{d,s} -> D_{s,d} D^*_{s,d}, and B_{d,s} -> D^*_{s,d} D^*_{s,d}
The amplitudes for decays of the type , have no
factorizable contributions, while , and have relatively small factorizable contributions
through the annihilation mechanism. The dominant contributions to the decay
amplitudes arise from chiral loop contributions and tree level amplitudes which
can be obtained in terms of soft gluon emissions forming a gluon condensate. We
predict that the branching ratios for the processes ,
and are all
of order , while ,
and are of
order . We obtain branching ratios for two 's in
the final state of order two times bigger.Comment: 15 pages, 4 figure
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