发表机构
ICRANet; Sapienza Università di Roma; INAF（国际相对论天体物理中心; 罗马第一大学; 意大利国家天体物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究仅从瞬时辐射确定GW170817喷流的角结构，发现其结构为2°至5°核心外$\epsilon\propto\theta^{-7.4}$，微弱性源于喷流结构，排除了四种常用结构。
AI 中文摘要
我们仅通过瞬时辐射（不借助余辉拟合、暴周密度或微物理参数）确定GW170817喷流的角结构。我们假设GRB 090510与GW170817属于同类外流，分别沿轴线和20°的干涉观测角被观测到。独立的引力波数据显示二者的双中子星质量和辐射能量兼容，为该假设提供了支撑。我们表明，对于观测到的喷流束充满外流的观测者，点源多普勒标度不适用：各向同性能量$E_{\rm iso}=4\pi\epsilon(\theta_v)$，其中$\epsilon$为视线方向单位立体角辐射的能量，而峰值能量满足$E_{\rm p,i}\propto\Gamma(\theta_v)$。我们从两个暴的比值中得到$n={\rm d}\ln\epsilon/{\rm d}\ln\Gamma = 3.76\pm0.29$，该结果无自由参数且未假设角度。这一结果以4.7σ至13σ的置信度排除了四种常用结构；在GW170817喷流峰值能量的全部报告范围内，仍有三种结构超过4σ的置信度。两条瞬时光谱未确定角尺度；结合GRB 090510的核心洛伦兹因子和观测角后，得到在2°至5°的核心外$\epsilon\propto\theta^{-7.4}$，这与从367个短暴推断出的宽度一致，外流在视线方向仍保持相对论性，洛伦兹因子$\Gamma=33$。该指数超过均匀共动流的洛伦兹加速所能产生的数值，因此该结构是外流的固有属性，而非加速的结果。同一结构确定了发射半径，其贡献了引力波信号与伽马射线之间1.74秒延迟中的0.41秒，其余延迟源于喷流的启动与 breakout，无自由参数。我们得出结论：（GW170817的）微弱性源于GW170817喷流的结构，而非明亮核心的去准直效应。
英文摘要
We determine the angular structure of the GW170817 jet by the prompt emission alone, without afterglow fitting, circumburst density or microphysical parameters. We assume that GRB 090510 and GW170817 have outflows of the same kind, observed respectively on-axis and at the interferometric viewing angle of $20^\circ$. We support this assumption with independent gravitational-wave data showing compatible binary masses and radiated energies. We show that for an observer whose beaming cone is filled with outflow, the point-source Doppler scalings do not apply: $E_{\rm iso}=4πε(θ_v)$, with $ε$ the energy radiated per unit solid angle along the line of sight, while the peak energy follows $E_{\rm p,i}\proptoΓ(θ_v)$. We obtain $n={\rm d}\lnε/{\rm d}\lnΓ= 3.76\pm0.29$ from the ratio of the two bursts, with no free parameter and no assumed angle. This excludes four structures in common use at $4.7σ$ to $13σ$; three remain above $4σ$ across the full reported range of the peak energy of the GW170817 jet. Two prompt spectra fix no angular scale; supplying it with the core Lorentz factor of GRB 090510 and the viewing angle gives $ε\proptoθ^{-7.4}$ outside a core of $2^\circ$--$5^\circ$, in agreement with the width inferred from $367$ short bursts, the outflow remaining relativistic at $Γ=33$ on the line of sight. The exponent exceeds what the Lorentz boost of a uniform comoving flow can produce, so the structure is intrinsic to the outflow and not a consequence of the boost. The same structure fixes the emission radius, which contributes $0.41$~s of the $1.74$~s delay between the gravitational-wave signal and the gamma-rays, the remainder being the launch and breakout of the jet, with no free parameters. We conclude that the faintness lies in the structure of the GW170817 jet, not in the de-beaming of a bright core.
Comments11 pages, 4 figures, including Supplemental Material
