2,168 research outputs found

    Statistical Properties of Multiple Optical Emission Components in Gamma-Ray Bursts and Implications

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    Well-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are complied from the literature. Multiple optical emission components are extracted with power-law function fits to these lightcurves. We present a systematical analysis for statistical properties and their relations to prompt gamma-ray emission and X-ray afterglow for each component. We show that peak luminosity in the prompt and late flares are correlated and the evolution of the peak luminosity may signal the evolution of the accretion rate. No tight correlation between the shallow decay phase/plateau and prompt gamma-ray emission is found. Assuming that they are due to a long-lasting wind injected by a compact object, we show that the injected behavior favors the scenarios of a long-lasting wind after the main burst episode. The peak luminosity of the afterglow onset is tightly correlated with Eiso, and it is dimmer as peaking later. Assuming that the onset bump is due to the fireball deceleration by the external medium, we examine the Gamma_0-Eiso relation and find that it is confirmed with the current sample. Optical re-brightening is observed in 30 GRBs in our sample. It shares the same relation between the width and the peak time as found in the onset bump, but no clear correlation between the peak luminosity and Eiso as observed in the onset bumps is found. Although its peak luminosity also decays with time, the slope is much shallower than that of the onset peak. We get L t^{-1}_{p}$, being consistent with off-axis observations to an expanding external fireball in a wind-like circum medium. The late re-brightening may signal another jet component. Mixing of different emission components may be the reason for the observed chromatic breaks in different energy bands.Comment: 10 pages, 5 figures, to be published by IJMPD (Proceedings of "The Third Galileo - Xu Guangqi meeting", Beijing, October 11-15, 2011

    Triangle singularity in the J/ψ→K+K−f0(980)(a0(980))J/\psi \rightarrow K^+ K^- f_0(980)(a_0(980)) decays

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    We study the J/ψ→K+K−f0(980)(a0(980))J/\psi \rightarrow K^+ K^- f_0(980)(a_0(980)) reaction and find that the mechanism to produce this decay develops a triangle singularity around Minv(K−f0/K−a0)≈1515M_{\rm inv}(K^- f_0/K^- a_0) \approx 1515~MeV. The differential width dΓ/dMinv(K−f0/K−a0)d\Gamma / dM_{\rm inv}(K^- f_0/K^- a_0) shows a rapid growth around the invariant mass being 1515~MeV as a consequence of the triangle singularity of this mechanism, which is directly tied to the nature of the f0(980)f_0(980) and a0(980)a_0(980) as dynamically generated resonances from the interaction of pseudoscalar mesons. The branching ratios obtained for the J/ψ→K+K−f0(980)(a0(980))J/\psi \rightarrow K^+ K^- f_0(980)(a_0(980)) decays are of the order of 10−510^{-5}, accessible in present facilities, and we argue that their observation should provide relevant information concerning the nature of the low-lying scalar mesons.Comment: 12 pages, 8 figures, published in EPJ

    Radioactive Decay of Specific Heavy Elements as an Energy Source for Late-Time Kilonovae and Potential JWST Observations

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    Revealing the temporal evolution of individual heavy elements synthesized in the merger ejecta from binary neutron star mergers not only improves our understanding of the origin of heavy elements beyond iron but also clarifies the energy sources of kilonovae. In this work, we present a comprehensive analysis of the temporal evolution of the energy fraction of each nuclide based on the rr-process nucleosynthesis simulations. The heavy elements dominating the kilonova emission within ∼100\sim100~days are identified, including 127^{127}Sb, 128^{128}Sb, 129^{129}Sb, 130^{130}Sb, 129^{129}Te, 132^{132}I, 222^{222}Rn, 223^{223}Ra, 224^{224}Ra, and 225^{225}Ac. It is found that the late-time kilonova light curve (t≳20t\gtrsim20~days) is highly sensitive to the presence of the heavy element 225^{225}Ac (with a half-life of 10.0~days). Our analysis shows that the James Webb Space Telescope (JWST), with its high sensitivity in the near-infrared band, is a powerful instrument for the identification of these specific heavy elements.Comment: 7 pages, 8 figures, accepted by MNRA

    Female media use behavior and agreement with publicly promoted agenda-specific health messages.

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    This study set out to explore the relationship between female media use behavior and agreement with agenda-specific publicly promoted health messages. A random digit dial telephone cross-sectional survey was conducted using a nationally representative sample of female residents aged 25 and over. Respondents' agreement with health messages was measured by a six-item Health Information Scale (HIS). Data were analyzed using chi-square tests and multiple logistic regression. This survey achieved a response rate of 86% (n = 1074). In this study the longest duration of daily television news watching (OR = 2.32), high self-efficacy (OR = 1.56), and greater attention to medical and health news (OR = 5.41) were all correlates of greater agreement with the selected health messages. Surprisingly, Internet use was not significant in the final model. Many women that public health interventions need to be targeting are not receptive to health information that can be accessed through Internet searches. However, they may be more readily targeted by television campaigns. Agenda-specific public health campaigns aiming to empower women to serve as nodes of information transmission and achieve efficient trickle down through the family unit might do better to invest more heavily in television promotion

    Event Rate of Fast Radio Burst from Binary Neutron-star Mergers

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    It is proposed that one-off fast radio burst (FRB) with periodic structures may be produced during the inspiral phase of a binary neutron-star (BNS) merger. In this paper, we study the event rate of such kind of FRB. We first investigate the properties of two one-off FRBs with periodic structures (i.e., FRB~20191221A and FRB~20210213A) in this scenario, by assuming the fast magnetosonic wave is responsible for their radio emission. For the luminosities and periods of these bursts, it is found that the pre-merger BNS with magnetic field strength B≳1012 GsB\gtrsim 10^{12}\,{\rm Gs} is required. This is relatively high compared with that of the most of the BNSs observed in our Galaxy, of which the magnetic field is around 109 Gs10^{9}\,{\rm Gs}. Since the observed BNSs in our Galaxy are the binaries without suffering merger, a credited event rate of BNS-merger originated FRBs should be estimated by considering the evolution of both the BNS systems and their magnetic fields. Based on the population synthesis and adopting a decaying magnetic field of NSs, we estimate the event rate of BNS-mergers relative to their final magnetic fields. We find that the rapid merged BNSs tend to merge with high magnetization, and the event rate of BNS-merger originated FRBs, i.e., the BNS-mergers with both NSs' magnetic field being higher than 1012 Gs10^{12}\,{\rm Gs} is ∼8×104 yr−1\sim8\times10^{4}\,\rm{yr}^{-1} (19%19 \% of the total BNS-mergers) in redshift z<1z<1.Comment: 11 pages, 2 figures, accepted for publication in Astrophysical Journa
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