Evidence for X-Ray Emission in Excess to the Jet-afterglow Decay 3.5 yr after the Binary Neutron Star Merger GW 170817: A New Emission Component
Evidence for X-Ray Emission in Excess to the Jet-afterglow Decay 3.5 yr after the Binary Neutron Star Merger GW 170817: A New Emission Component
复制标题
DOI：
10.3847/2041-8213/ac504a
复制
发表时间：
2021-04
期刊：
影响因子：
--
通讯作者：
A. Hajela;R. Margutti;J. Bright;K. Alexander;B. Metzger;V. Nedora;A. Kathirgamaraju;B. Margalit;D. Radice;C. Guidorzi;E. Berger;A. MacFadyen;D. Giannios;R. Chornock;I. Heywood;L. Sironi;O. Gottlieb;D. Coppejans;T. Laskar;Y. Cendes;R. Duran;T. Eftekhari;W. Fong;A. McDowell;M. Nicholl;X. Xie;J. Zrake;S. Bernuzzi;F. Broekgaarden;C. Kilpatrick;G. Terreran;V. Villar;P. Blanchard;S. Gomez;G. Hosseinzadeh;D. Matthews;J. Rastinejad
中科院分区：
文献类型：
--
作者：
A. Hajela;R. Margutti;J. Bright;K. Alexander;B. Metzger;V. Nedora;A. Kathirgamaraju;B. Margalit;D. Radice;C. Guidorzi;E. Berger;A. MacFadyen;D. Giannios;R. Chornock;I. Heywood;L. Sironi;O. Gottlieb;D. Coppejans;T. Laskar;Y. Cendes;R. Duran;T. Eftekhari;W. Fong;A. McDowell;M. Nicholl;X. Xie;J. Zrake;S. Bernuzzi;F. Broekgaarden;C. Kilpatrick;G. Terreran;V. Villar;P. Blanchard;S. Gomez;G. Hosseinzadeh;D. Matthews;J. Rastinejad
在双中子星合并事件GW 170817后3年的第一个∼中，射电和X射线辐射主要是由合并900d后传播到n值为n900的低密度介质中的结构相对论离轴喷流所发出的辐射。对于L x≈5×1038erg S−1的1234天，最近探测到的X射线发射代表着≥3.2σ(高斯当量)偏离了早期最适合多波长余辉的普遍的喷流后模型。在JetFit余辉模型的背景下，当前的数据表示具有统计意义的偏离≥3.1σ，这取决于火球的准直，最真实的模型显示在≥3.7σ的水平上过度。缺乏可探测到的3 GHz射电发射表明，比喷流余辉更难获得宽带频谱。这些性质与一种新的发射成分的出现是一致的，例如由膨胀的合并喷发产生的温和相对论激波产生的同步辐射，即千诺瓦余辉。在此背景下，我们提出了一组从头算数值相对论双中子星(BNS)合并模拟，表明X射线过剩支持合并抛射中高速尾巴的存在，并反对合并残余物迅速崩塌成黑洞。致密天体残骸上的吸积过程产生的辐射是一种可行的替代方案。既没有观测到千诺瓦余辉，也没有观测到吸积动力发射，因为在这个演化阶段检测到BNS合并是史无前例的。
For the first ∼3 yrs after the binary neutron star merger event GW 170817, the radio and X-ray radiation has been dominated by emission from a structured relativistic off-axis jet propagating into a low-density medium with n 900 days after the merger. With L x ≈ 5 × 1038 erg s−1 at 1234 days, the recently detected X-ray emission represents a ≥3.2σ (Gaussian equivalent) deviation from the universal post-jet-break model that best fits the multiwavelength afterglow at earlier times. In the context of JetFit afterglow models, current data represent a departure with statistical significance ≥3.1σ, depending on the fireball collimation, with the most realistic models showing excesses at the level of ≥3.7σ. A lack of detectable 3 GHz radio emission suggests a harder broadband spectrum than the jet afterglow. These properties are consistent with the emergence of a new emission component such as synchrotron radiation from a mildly relativistic shock generated by the expanding merger ejecta, i.e., a kilonova afterglow. In this context, we present a set of ab initio numerical relativity binary neutron star (BNS) merger simulations that show that an X-ray excess supports the presence of a high-velocity tail in the merger ejecta, and argues against the prompt collapse of the merger remnant into a black hole. Radiation from accretion processes on the compact-object remnant represents a viable alternative. Neither a kilonova afterglow nor accretion-powered emission have been observed before, as detections of BNS mergers at this phase of evolution are unprecedented.