349 research outputs found

    Electromagnetic counterparts of binary neutron star mergers leading to a strongly magnetized long-lived remnant neutron star

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    We explore the electromagnetic counterparts that will associate with binary neutron star mergers for the case that remnant massive neutron stars survive for 0.5\gtrsim 0.5 s after the merger. For this study, we employ the outflow profiles obtained by long-term general-relativistic neutrino-radiation magneto-hydrodynamics simulations with a mean field dynamo effect. We show that a synchrotron afterglow with high luminosity can be associated with the merger event if the magnetic fields of the remnant neutron stars are significantly amplified by the dynamo effect. We also perform a radiative transfer calculation for kilonovae and find that for the highly amplified magnetic field cases, the kilonovae can be bright in the early epoch (t0.5dt\leq 0.5\,{\rm d}), while it shows rapid declining (1d\lesssim 1\,{\rm d}) emission and long-lasting (10d\sim 10\,{\rm d}) emission in the optical and near-infrared wavelength, respectively. All these features have not been found in GW170817, indicating that the merger remnant neutron star formed in GW170817 might have collapsed to a black hole within several hundreds ms or magnetic-field amplification might be a minor effect

    Self-consistent picture of the mass ejection from a one second-long binary neutron star merger leaving a short-lived remnant in general-relativistic neutrino-radiation magnetohydrodynamic simulation

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    We perform a general-relativistic neutrino-radiation magnetohydrodynamicsimulation of a one second-long binary neutron star merger on Japanesesupercomputer Fugaku using about 7272 million CPU hours with 20,73620,736 CPUs. Weconsider an asymmetric binary neutron star merger with masses of 1.21.2 and1.5M1.5M_\odot and a `soft' equation of state SFHo. It results in a short-livedremnant with the lifetime of 0.017\approx 0.017\,s, and subsequent massive torusformation with the mass of 0.05M\approx 0.05M_\odot after the remnant collapses toa black hole. For the first time, we confirm that after the dynamical massejection, which drives the fast tail and mildly relativistic components, thepost-merger mass ejection from the massive torus takes place due to themagnetorotational instability-driven turbulent viscosity and the two ejectacomponents are seen in the distributions of the electron fraction and velocitywith distinct features.<br

    General-relativistic neutrino-radiation magnetohydrodynamics simulation of black hole-neutron star mergers for seconds

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    Seconds-long numerical-relativity simulations for black hole-neutron star mergers are performed for the first time to obtain a self-consistent picture of the merger and post-merger evolution processes. To investigate the case that tidal disruption takes place, we choose the initial mass of the black hole to be 5.4M5.4M_\odot or 8.1M8.1M_\odot with the dimensionless spin of 0.75. The neutron-star mass is fixed to be 1.35M1.35M_\odot. We find that after the tidal disruption, dynamical mass ejection takes place spending 10ms\lesssim 10\,{\rm ms} together with the formation of a massive accretion disk. Subsequently, the magnetic field in the disk is amplified by the magnetic winding and magnetorotational instability, establishing a turbulent state and inducing the angular momentum transport. The post-merger mass ejection by the magnetically-induced viscous effect sets in at 300\sim 300-500ms500\,{\rm ms} after the tidal disruption, at which the neutrino luminosity drops below 1051.5erg/s\sim 10^{51.5}\,{\rm erg/s}, and continues for several hundreds ms. A magnetosphere near the rotational axis of the black hole is developed after the matter and magnetic flux fall into the black hole from the accretion disk, and high-intensity Poynting flux generation sets in at a few hundreds ms after the tidal disruption. The intensity of the Poynting flux becomes low after the significant post-merger mass ejection, because the opening angle of the magnetosphere increases. The lifetime for the stage with the strong Poynting flux is 11-2s2\,{\rm s}, which agrees with the typical duration of short-hard gamma-ray bursts

    A low-mass binary neutron star: long-term ejecta evolution and kilonovae with weak blue emission

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    We study the long-term evolution of ejecta formed in a binary neutron star (BNS) merger that results in a long-lived remnant NS by performing a hydrodynamics simulation with the outflow data of a numerical relativity simulation as the initial condition. At the homologously expanding phase, the total ejecta mass reaches 0.1M\approx0.1\,M_\odot with an average velocity of 0.1c\approx0.1\,c and lanthanide fraction of 0.005\approx 0.005. We further perform the radiative transfer simulation employing the obtained ejecta profile. We find that, contrary to a naive expectation from the large ejecta mass and low lanthanide fraction, the optical emission is not as bright as that in GW170817/AT2017gfo, while the infrared emission can be brighter. This light curve property is attributed to preferential diffusion of photons toward the equatorial direction due to the prolate ejecta morphology, large opacity contribution of Zr, Y, and lanthanides, and low specific heating rate of the ejecta. Our results suggest that these light curve features could be used as an indicator for the presence of a long-lived remnant NS. We also found that the bright optical emission broadly consistent with GW170817/AT2017gfo is realized for the case that the high-velocity ejecta components in the polar region are suppressed. These results suggest that the remnant in GW170817/AT2017gfo is unlikely to be a long-lived NS, but might have collapsed to a black hole within O(0.1){\cal O}(0.1) s

    An information-bearing seed for nucleating algorithmic self-assembly

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    Self-assembly creates natural mineral, chemical, and biological structures of great complexity. Often, the same starting materials have the potential to form an infinite variety of distinct structures; information in a seed molecule can determine which form is grown as well as where and when. These phenomena can be exploited to program the growth of complex supramolecular structures, as demonstrated by the algorithmic self-assembly of DNA tiles. However, the lack of effective seeds has limited the reliability and yield of algorithmic crystals. Here, we present a programmable DNA origami seed that can display up to 32 distinct binding sites and demonstrate the use of seeds to nucleate three types of algorithmic crystals. In the simplest case, the starting materials are a set of tiles that can form crystalline ribbons of any width; the seed directs assembly of a chosen width with >90% yield. Increased structural diversity is obtained by using tiles that copy a binary string from layer to layer; the seed specifies the initial string and triggers growth under near-optimal conditions where the bit copying error rate is 17 kb of sequence information. In sum, this work demonstrates how DNA origami seeds enable the easy, high-yield, low-error-rate growth of algorithmic crystals as a route toward programmable bottom-up fabrication

    Self-Assembly of 4-sided Fractals in the Two-handed Tile Assembly Model

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    We consider the self-assembly of fractals in one of the most well-studied models of tile based self-assembling systems known as the Two-handed Tile Assembly Model (2HAM). In particular, we focus our attention on a class of fractals called discrete self-similar fractals (a class of fractals that includes the discrete Sierpi\'nski carpet). We present a 2HAM system that finitely self-assembles the discrete Sierpi\'nski carpet with scale factor 1. Moreover, the 2HAM system that we give lends itself to being generalized and we describe how this system can be modified to obtain a 2HAM system that finitely self-assembles one of any fractal from an infinite set of fractals which we call 4-sided fractals. The 2HAM systems we give in this paper are the first examples of systems that finitely self-assemble discrete self-similar fractals at scale factor 1 in a purely growth model of self-assembly. Finally, we show that there exists a 3-sided fractal (which is not a tree fractal) that cannot be finitely self-assembled by any 2HAM system

    Optimal self-assembly of finite shapes at temperature 1 in 3D

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    Working in a three-dimensional variant of Winfree's abstract Tile Assembly Model, we show that, for an arbitrary finite, connected shape XZ2X \subset \mathbb{Z}^2, there is a tile set that uniquely self-assembles into a 3D representation of a scaled-up version of XX at temperature 1 in 3D with optimal program-size complexity (the "program-size complexity", also known as "tile complexity", of a shape is the minimum number of tile types required to uniquely self-assemble it). Moreover, our construction is "just barely" 3D in the sense that it only places tiles in the z=0z = 0 and z=1z = 1 planes. Our result is essentially a just-barely 3D temperature 1 simulation of a similar 2D temperature 2 result by Soloveichik and Winfree (SICOMP 2007)

    Study of double pion photoproduction on the deuteron

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    AbstractThe π+π− photoproductions on the proton and deuteron have been studied in a photon energy range of 0.8–1.1 GeV at the Laboratory of Nuclear Science, Tohoku University. Charged pions and protons were detected using Neutral Kaon Spectrometer. We obtained the cross sections for the p(γ,pπ+π−) and d(γ,pπ+π−)n. The quasi-free process with a neutron spectator was extracted by the neutron momentum cut of pn>0.3 GeV/c. The cross section for the Δ++Δ− production was deduced in the non-quasi-free process of the γd→pnπ+π−. It was 13.4±0.4 μb at Eγ=0.82 GeV
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