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Reduced transition probabilities for 4He radiative capturereactions at astrophysical energies

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Research in Astronomy and Astrophysics 2014年第3期14卷 367-372页

作者： Hossein Sadeghi Reza Ghasemi Department of Physics Faculty of ScienceArak University

The reduced transition probabilities from an electric quadrupole B（E2） andreduced transition probabilities from a magnetic dipole B（M1） between the groundstate and the first excited state have been calculated for the 3He（α,γ）7Be, 8Be（α,γ）12cand 12C（α,γ）160 radiative capture reactions with the M3Y potential. These reactionsare important in stellar evolution. The calculated B（M1） and B（E2） for 7Be nuclei arefound to be 1.082 x 10-3 e2 fm2 and 1.921 e2 fma from transitions 3/2- to 1/2-, re-spectively. The obtained values for reduced transition probabilities B（E2） for the 12Cand 160 nuclei from transitions 0＋ to 2＋ are 12.54 e2 fm4 and 14.18 e2 fm4, respec-tively. The results are in satisfactory agreement with available experimental data.

关键词： nuclear reactions abundances methods: numerical

Detecting radio afterglows of gamma-ray bursts with FAST

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Research in Astronomy and Astrophysics 2015年第2期15卷 237-251页

作者： Zhi-Bin Zhang Si-Wei Kong Yong-Feng Huang Di Li Long-Biao Li Department of Physics College of Sciences Guizhou University Key Laboratory for Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Department of Astronomy Nanjing University National Astronomical Observatories Chinese Academy of Sciences

Using the generic hydrodynamic model of gamma-ray burst （GRB） after- glows, we calculate the radio afterglow light curves of low luminosity, high luminosity, failed and standard GRBs in different observational bands of FAST＇s energy window. The GRBs are assumed to be located at different distances from us. Our results rank the detectability of GRBs in descending order as high luminosity, standard, failed and low luminosity GRBs. We predict that almost all types of radio afterglows except those of low luminosity GRBs could be observed by a large radio telescope as long as the domains of time and frequency are appropriate. It is important to note that FAST can detect relatively weak radio afterglows at a higher frequency of 2.5 GHz for very high redshift up to z = 15 or even more. Radio afterglows of low luminosity GRBs can only be detected after the completion of the second phase of FAST. FAST is expected to significantly expand the sample of GRB radio afterglows in the near future.

关键词： gamma rays: bursts methods: numerical telescopes

PHoToNs–A parallel heterogeneous and threads oriented code for cosmological N-body simulation

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Research in Astronomy and Astrophysics 2018年第6期18卷 7-16页

作者： Qiao Wang Zong-Yan Cao Liang Gao Xue-Bin Chi Chen Meng Jie Wang Long Wang Key Laboratory of Computational Astrophysics National Astronomical Observatories Chinese Academy of Sciences Supercomputing Center Computer Network Information Center Chinese Academy of Sciences Institute for Computational Cosmology Department of Physics Durham University Science Laboratories System Department Baidu Group Ltd.

We introduce a new code for cosmological simulations, PHo To Ns, which incorporates features for performing massive cosmological simulations on heterogeneous high performance computer(HPC) systems and threads oriented programming. PHo To Ns adopts a hybrid scheme to compute gravitational force, with the conventional Particle-Mesh(PM) algorithm to compute the long-range force,the Tree algorithm to compute the short range force and the direct summation Particle-Particle(PP) algorithm to compute gravity from very close particles. A self-similar space filling a Peano-Hilbert curve is used to decompose the computing domain. Threads programming is advantageously used to more flexibly manage the domain communication, PM calculation and synchronization, as well as Dual Tree Traversal on the CPU+MIC platform. PHo To Ns scales well and efficiency of the PP kernel achieves68.6% of peak performance on MIC and 74.4% on CPU platforms. We also test the accuracy of the code against the much used Gadget-2 in the community and found excellent agreement.

关键词： methods: numerical galaxies: interactions dark matter

An axion-like scalar field environment effect on binary black hole merger

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Research in Astronomy and Astrophysics 2018年第6期18卷 35-48页

作者： Qing Yang Li-Wei Ji Bin Hu Zhou-Jian Cao Rong-Gen Cai Department of Astronomy Beijing Normal University Beijing 100875 China CAS Key Laboratory of Theoretical Physics Institute of Theoretical Physics Chinese Academy of SciencesBeijing 100190 China School of Physical Sciences University of Chinese Academy of Sciences Beijing 100049 China

The environment, such as an accretion disk, could modify the signal of the gravitational wave from astrophysical black hole binaries. In this article, we model the matter field around intermediatemass binary black holes by means of an axion-like scalar field and investigate their joint evolution. In detail, we consider equal mass binary black holes surrounded by a shell of axion-like scalar field both in spherically symmetric and non-spherically symmetric cases, and with different strengths of the scalar field. Our result shows that the environmental scalar field could essentially modify the dynamics. Firstly,in the spherically symmetric case, with increase of the scalar field strength, the number of circular orbits for the binary black hole is reduced. This means that the scalar field could significantly accelerate the merger process. Secondly, once the scalar field strength exceeds a certain critical value, the scalar field could collapse into a third black hole with its mass being larger than that of the binary. Consequently,the new black hole that collapses from the environmental scalar field could accrete the binary promptly and the binary collides head-on with each other. In this process, there is almost no quadrupole signal produced, and, consequently, the gravitational wave is greatly suppressed. Thirdly, when the scalar field strength is relatively smaller than the critical value, the black hole orbit could develop eccentricity through accretion of the scalar field. Fourthly, during the initial stage of the inspiral, the gravitational attractive force from the axion-like scalar field could induce a sudden turn in the binary orbits, hence resulting in a transient wiggle in the gravitational waveform. Finally, in the non-spherical case, the scalar field could gravitationally attract the binary moving toward the center of mass for the scalar field and slow down the merger process.

关键词： stars: black holes gravitational waves methods: numerical