33,497 research outputs found
Polarization of kilonova emission from a black hole-neutron star merger
A multi-messenger, black hole (BH) - neutron star (NS) merger event still
remains to be detected. The tidal (dynamical) ejecta from such an event,
thought to produce a kinonova, is concentrated in the equatorial plane and
occupies only part of the whole azimuthal angle. In addition, recent
simulations suggest that the outflow or wind from the post-merger remnant disk,
presumably anisotropic, can be a major ejecta component responsible for a
kilonova. For any ejecta whose photosphere shape deviates from the spherical
symmetry, the electron scattering at the photosphere causes a net polarization
in the kilonova light. Recent observational and theoretical polarization
studies have been focused to the NS-NS merger kilonova AT2017gfo. We extend
those work to the case of a BH-NS merger kilonova. We show that the degree of
polarization at the first hr can be up to 3\% if a small amount
() of free neutrons have survived in the fastest component
of the dynamical ejecta, whose beta-decay causes a precursor in the kilonova
light. The polarization degree can be 0.6\% if free neutrons survived in
the fastest component of the disk wind. Future polarization detection of a
kilonova will constrain the morphology and composition of the dominant ejecta
component, therefore help to identify the nature of the merger.Comment: 10 pages, 5 figures. Accepted for publication in Ap
Alexis de Tocqueville; chronicler of the American democratic experiment
[Abstract]: The purpose of this work is to develop an interactive tool which helps botanists to extract the vein system with its hierarchical properties with as little user interaction as possible. In this paper, we present a new venation extraction method using independent component analysis (ICA). The popular and efficient FastICA algorithm is applied to patches of leaf images to learn a set of linear basis functions or features for the images and then the basis functions are used as the pattern map for vein extraction. In our experiments, the training sets are randomly generated from different leaf images. Experimental results demonstrate that ICA is a promising technique for extracting leaf veins and edges of objects. ICA, therefore, can play an important role in automatically identifying living plants
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