42,038 research outputs found
Strong GeV Emission Accompanying TeV Blazar H1426+428
For High frequency BL Lac objects (HBLs) like H1426+428, a significant
fraction of their TeV gamma-rays emitted are likely to be absorbed in
interactions with the diffuse IR background, yielding pairs. The
resulting pairs generate one hitherto undiscovered GeV emission by
inverse Compton scattering with the cosmic microwave background photons
(CMBPs). We study such emission by taking the 1998-2000 CAT data, the
reanalyzed 1999 & 2000 HEGRA data and the corresponding intrinsic spectra
proposed by Aharonian et al. (2003a). We numerically calculate the scattered
photon spectra for different intergalactic magnetic field (IGMF) strengths. If
the IGMF is about or weaker, there comes very strong GeV
emission, whose flux is far above the detection sensitivity of the upcoming
satellite GLAST! Considered its relatively high redshift (), the
detected GeV emission in turn provides us a valuable chance to calibrate the
poor known spectral energy distribution of the intergalactic infrared
background, or provides us some reliable constraints on the poorly known IGMF
strength.Comment: 5 pages, 1 figure. A&A in Pres
The Ultraviolet flash accompanying GRBs from neutron-rich internal shocks
In the neutron-rich internal shocks model for Gamma-ray Burts (GRBs), the
Lorentz factors (LFs) of ions shells are variable, so are the LFs of
accompanying neutron shells. For slow neutron shells with a typical LF tens,
the typical beta-decay radius reads R_{\beta,s} several 10^{14} cm, which is
much larger than the typical internal shocks radius 10^{13} cm, so their impact
on the internal shocks may be unimportant. However, as GRBs last long enough
(T_{90}>20(1+z) s), one earlier but slower ejected neutron shell will be swept
successively by later ejected ion shells in the range 10^{13}-10^{15} cm, where
slow neutrons have decayed significantly. We show in this work that ion shells
interacting with the beta-decay products of slow neutron shells can power a
ultraviolet (UV) flash bright to 12th magnitude during the prompt gamma-ray
emission phase or slightly delayed, which can be detected by the upcoming
Satellite SWIFT in the near future.Comment: 6 pages (2 eps figures), accepted for publication in ApJ
Rescattering effects in B_{u,d,s}(bar) to D P, D(bar) P decays
We study quasi-elastic rescattering effects in B_{u,d,s}(bar) to DP, D(bar)P
decays, where P is a light pseudoscalar. The updated measurements of
B_{u,d}(bar) to DP decays are used to extract the effective Wilson coefficients
a^{eff}_1 ~ 0.90, a^{eff}_2 ~ 0.23, three strong phases delta ~ 53 degree,
theta ~ 18 degree, sigma ~ -88 degree, and the mixing angle tau ~ 9 degree.
This information is used to predict rates of nineteen B_{s}(bar) to DP and
B_{u,d,s}(bar) to D(bar)P decay modes, including modes of interests in the
gamma/phi_3 program. Many decay rates are found to be enhanced. In particular,
the B_s(bar) to D0 K0 rate is predicted to be 8\times 10^{-4}, which could be
measured soon. The rescattering effects on the corresponding B_{u,d,s}(bar) to
D(bar)P, DP amplitude ratios r_B, r_{B_s}, and the relative strong phases
delta_B, delta_{B_s} are studied. Although the decay rates are enhanced in most
cases, r_{B,B_s} values are similar to factorization expectation.Comment: 16 page
Probability-dependent gain-scheduled filtering for stochastic systems with missing measurements
Copyright @ 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.This brief addresses the gain-scheduled filtering problem for a class of discrete-time systems with missing measurements, nonlinear disturbances, and external stochastic noise. The missing-measurement phenomenon is assumed to occur in a random way, and the missing probability is time-varying with securable upper and lower bounds that can be measured in real time. The multiplicative noise is a state-dependent scalar Gaussian white-noise sequence with known variance. The addressed gain-scheduled filtering problem is concerned with the design of a filter such that, for the admissible random missing measurements, nonlinear parameters, and external noise disturbances, the error dynamics is exponentially mean-square stable. The desired filter is equipped with time-varying gains based primarily on the time-varying missing probability and is therefore less conservative than the traditional filter with fixed gains. It is shown that the filter parameters can be derived in terms of the measurable probability via the semidefinite program method.This work was supported in part by the Leverhulme Trust of the U.K., the Engineering and Physical Sciences Research Council (EPSRC) of the U.K. under Grant GR/S27658/01, the National Natural Science Foundation of China under Grants 61028008, 61074016 and 60974030, the Shanghai Natural
Science Foundation of China under Grant 10ZR1421200, and the Alexander von Humboldt Foundation of Germany
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