中子星并合的第一缕光：短伽马射线暴喷流驱动的偏轴茧冷却X射线辐射
First Light of Neutron Star Mergers: Off-axis Cocoon Cooling X-ray Emission from Short Gamma-Ray Burst Jets
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- School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）
- Department of Astronomy and Theoretical Astrophysics Center, University of California, Berkeley（加州大学伯克利分校天文学与理论天体物理中心）
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中文总结 AI 辅助
本文通过流体动力学模拟和辐射后处理，发现短伽马射线暴喷流驱动的茧冷却产生偏轴X射线瞬变，可被爱因斯坦探针探测，为识别中子星并合提供早期电磁对应体。
中文摘要 AI 辅助
中子星并合（NSMs）是已确认的引力波源。因此，为这些事件识别早期电磁对应体对于快速定位和多信使后续观测至关重要。然而，与之相关的伽马射线暴（GRBs）高度准直，因此容易被偏轴观测者错过。一个早期的、较少成束的对应体对于识别大多数并合事件至关重要。在本快报中，我们研究了由短伽马射线暴喷流穿过并合抛射物所产生的喷流驱动茧的冷却辐射。我们进行了流体动力学模拟和辐射后处理，以计算在宽泛视角范围内的早期X射线辐射。我们发现，中等相对论性茧为偏轴观测者产生明亮的软X射线瞬变，其光度为$10^{46-48}{\rm erg\\,s^{-1}}$，持续时间为几秒到十秒。X射线光谱是准热谱，特征温度为$0.1$--$1\\,{\rm keV}$。对于视角$\theta_{\rm v}=10^{\circ}$的观测者，茧辐射可被爱因斯坦探针（EP）探测到红移$z\simeq 0.3$。对于像GW170817这样的邻近事件，它仍然可探测到视角$\theta_{\rm v}\simeq 45^{\circ}$。在典型模型中，EP的预测探测率为$0.5\\,{\rm yr^{-1}}$。在未来的多信使观测活动中，对此类X射线触发的快速紫外/光学/红外后续观测可以随后识别相关的千新星和喷流余辉辐射，这将确认其起源。
英文摘要
Neutron star mergers (NSMs) are confirmed gravitational wave sources. Identifying an early electromagnetic counterpart for these events is therefore crucial for rapid localization and multimessenger follow-up. However, the associated Gamma-Ray Bursts (GRBs) are highly collimated and are therefore easily missed by off-axis observers. An early, less beamed counterpart is essential for identifying the majority of mergers. In this Letter, we investigate the cooling emission from jet-driven cocoons produced by short gamma-ray burst jets propagating through merger ejecta. We perform hydrodynamic simulations and radiative post-processing to calculate the early X-ray emission over a wide range of viewing angles. We find that the mildly relativistic cocoon produces bright soft X-ray transients for off-axis observers, with luminosities of $10^{46-48}{\rm erg\,s^{-1}}$ and durations of a few to ten seconds. The X-ray spectra are quasi-thermal with characteristic temperatures of $0.1$--$1\,{\rm keV}$. For observers at $θ_{\rm v}=10^{\circ}$, the cocoon emission is detectable by Einstein Probe (EP) out to $z\simeq 0.3$. For nearby events like GW170817, it remains detectable up to $θ_{\rm v}\simeq 45^{\circ}$. The predicted detection rate for EP is $0.5\,{\rm yr^{-1}}$ in the canonical model. In future multimessenger campaigns, rapid UV/optical/IR follow-up of such X-ray triggers can subsequently identify the associated kilonova and jet afterglow emission, which will confirm the origin.
