2,148 research outputs found
IceCube Non-detection of GRBs: Constraints on the Fireball Properties
The increasingly deep limit on the neutrino emission from gamma-ray bursts
(GRBs) with IceCube observations has reached the level that could put useful
constraints on the fireball properties. We first present a revised analytic
calculation of the neutrino flux, which predicts a flux an order of magnitude
lower than that obtained by the IceCube collaboration. For benchmark model
parameters (e.g. the bulk Lorentz factor is \Gamma=10^{2.5}, the observed
variability time for long GRBs is t_v=0.01 s and the ratio between the energy
in accelerated protons and in radiation is \eta_p=10 for every burst) in the
standard internal shock scenario, the predicted neutrino flux from 215 bursts
during the period of the 40-string and 59-string configurations is found to be
a factor of ~3 below the IceCube sensitivity. However, if we accept the
recently found inherent relation between the bulk Lorentz factor and burst
energy, the expected neutrino flux increases significantly and the spectral
peak shifts to lower energy. In this case, the non-detection then implies that
the baryon loading ratio should be \eta_p<10 if the variability time of long
GRBs is fixed to t_v=0.01 s. Instead, if we relax the standard internal shock
scenario but keep to assume \eta_p=10, the non-detection constrains the
dissipation radius to be R>4x10^{12} cm assuming the same dissipation radius
for every burst and benchmark parameters for fireballs. We also calculate the
diffuse neutrino flux from GRBs for different luminosity functions existing in
the literature. The expected flux exceeds the current IceCube limit for some
luminosity functions, and thus the non-detection constrains \eta_p<10 in such
cases when the variability time of long GRBs is fixed to t_v=0.01 s.Comment: Accepted by ApJ, 14 pages, 5 figures, typos corrected, scheduled for
the June 10, 2012, v752 - 1 issu
KD-EKF: A Consistent Cooperative Localization Estimator Based on Kalman Decomposition
In this paper, we revisit the inconsistency problem of EKF-based cooperative
localization (CL) from the perspective of system decomposition. By transforming
the linearized system used by the standard EKF into its Kalman observable
canonical form, the observable and unobservable components of the system are
separated. Consequently, the factors causing the dimension reduction of the
unobservable subspace are explicitly isolated in the state propagation and
measurement Jacobians of the Kalman observable canonical form. Motivated by
these insights, we propose a new CL algorithm called KD-EKF which aims to
enhance consistency. The key idea behind the KD-EKF algorithm involves perform
state estimation in the transformed coordinates so as to eliminate the
influencing factors of observability in the Kalman observable canonical form.
As a result, the KD-EKF algorithm ensures correct observability properties and
consistency. We extensively verify the effectiveness of the KD-EKF algorithm
through both Monte Carlo simulations and real-world experiments. The results
demonstrate that the KD-EKF outperforms state-of-the-art algorithms in terms of
accuracy and consistency
Extremely Strong ^{13}CO J=3-2 Line in the "Water Fountain" IRAS 16342-3814: Evidence for the Hot-Bottom Burning
We observed four "water fountain" sources in the CO J=3-2 line emission with
the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in
2010-2011. The water fountain sources are evolved stars that form high-velocity
collimated jets traced by water maser emission. The CO line was detected only
from IRAS 16342-3814. The present work confirmed that the ^{12}CO to ^{13}CO
line intensity ratio is ~1.5 at the systemic velocity. We discuss the origins
of the very low ^{12}CO to ^{13}CO intensity ratio, as possible evidence for
the "hot-bottom burning" in an oxygen-rich star, and the CO intensity variation
in IRAS 16342-3814.Comment: 10 pages, 3 figures, accepted for publication to the Publications of
the Astronomical Society of Japan, Vol. 64, No.
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