The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum
The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum
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DOI：
10.3847/2041-8213/aab2ad
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发表时间：
2018-01
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通讯作者：
R. Margutti;K. Alexander;Xiaoyi Xie;L. Sironi;B. Metzger;A. Kathirgamaraju;W. Fong;P. Blanchard;E. Berger;A. MacFadyen;D. Giannios;C. Guidorzi;A. Hajela;R. Chornock;P. Cowperthwaite;T. Eftekhari;M. Nicholl;V. Villar;P. G. Williams;J. Zrake
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作者：
R. Margutti;K. Alexander;Xiaoyi Xie;L. Sironi;B. Metzger;A. Kathirgamaraju;W. Fong;P. Blanchard;E. Berger;A. MacFadyen;D. Giannios;C. Guidorzi;A. Hajela;R. Chornock;P. Cowperthwaite;T. Eftekhari;M. Nicholl;V. Villar;P. G. Williams;J. Zrake
本文报道了钱德拉深X射线天文台（CXO）、哈勃空间望远镜（HST）和卡尔·Jansky甚大阵（VLA）对双星星星事件GW 170817在合并后t < 160天的观测结果。这些观测结果表明，GW 170817已经随着时间的推移而稳定地变亮，现在可能已经达到了峰值，并将发射过程限制为非热同步辐射，其中冷却频率νc高于X射线波段，同步辐射频率νm低于无线电波段。非常简单的幂律谱扩展到8个数量级的频率，使最精确的测量指数p的分布的非热相对论性电子加速的冲击发射的中子星星（NS）-NS合并日期。我们发现p = 2.17 ± 0.01，这表明来自具有Γ π 3-10的喷出物的辐射占观测到的辐射的主导地位。虽然限制了发射过程的性质，但这些观测结果并没有限制相对论喷出物的性质。我们采用模拟NS喷出物云发射的爆炸外流表明，从GW 170817的非热发射的光谱和时间演变是一致的，从径向分层准球形喷出物在温和的相对论速度行驶的排放，并从离轴准直喷出物的特点是一个狭窄的超相对论材料锥较慢的翅膀延伸到更大的角度发射。在后一种情况下，GW 170817隐藏着一个正常的短伽马射线暴（SGRB），远离我们的视线。在t ≤ 200天的观测不太可能解决这一争论，因为在这两种情况下，观测到的辐射实际上都是由温和相对论性物质的辐射主导的。
We report deep Chandra X-ray Observatory (CXO), Hubble Space Telescope (HST), and Karl J. Jansky Very Large Array (VLA) observations of the binary neutron star event GW170817 at t < 160 days after merger. These observations show that GW170817 has been steadily brightening with time and might have now reached its peak, and constrain the emission process as non-thermal synchrotron emission where the cooling frequency νc is above the X-ray band and the synchrotron frequency νm is below the radio band. The very simple power-law spectrum extending for eight orders of magnitude in frequency enables the most precise measurement of the index p of the distribution of non-thermal relativistic electrons accelerated by a shock launched by a neutron star (NS)–NS merger to date. We find p = 2.17 ± 0.01, which indicates that radiation from ejecta with Γ ∼ 3–10 dominates the observed emission. While constraining the nature of the emission process, these observations do not constrain the nature of the relativistic ejecta. We employ simulations of explosive outflows launched in NS ejecta clouds to show that the spectral and temporal evolution of the non-thermal emission from GW170817 is consistent with both emission from radially stratified quasi-spherical ejecta traveling at mildly relativistic speeds, and emission from off-axis collimated ejecta characterized by a narrow cone of ultra-relativistic material with slower wings extending to larger angles. In the latter scenario, GW170817 harbored a normal short gamma-ray burst (SGRB) directed away from our line of sight. Observations at t ≤ 200 days are unlikely to settle the debate, as in both scenarios the observed emission is effectively dominated by radiation from mildly relativistic material.