ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C
ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C
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DOI：
10.3847/2041-8213/ab2247
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发表时间：
2019-04
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通讯作者：
T. Laskar;K. Alexander;R. Gill;J. Granot;E. Berger;C. Mundell;Rodolfo Barniol-Duran;J. Bolmer;P. Duffell;H. V. Eerten;W. Fong;S. Kobayashi;R. Margutti;P. Schady
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文献类型：
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作者：
T. Laskar;K. Alexander;R. Gill;J. Granot;E. Berger;C. Mundell;Rodolfo Barniol-Duran;J. Bolmer;P. Duffell;H. V. Eerten;W. Fong;S. Kobayashi;R. Margutti;P. Schady
我们提出了阿塔卡玛大型毫米/亚毫米阵列97.5 GHz的总强度和线性偏振观测的毫米波段余辉的GRB 190114 C跨越2.2-5.2小时后爆发。我们探测到的线偏振在0.5 σ水平，从0.87 ± 0.13）%下降到（0.60 ± 0.19）%，偏振位置角在观测过程中从（10 ± 5）°演变到（−44 ± 12）°。这是首次探测和测量γ射线暴中偏振射电/毫米波发射的时间演化。我们表明，光学和X射线观测之间的0.03天和100.3天是一致的快速冷却的前向冲击扩展到风的环境。然而，在0.03天的光学观测，以及无线电和毫米波观测，来自一个单独的组成部分，我们解释为从反向冲击喷出物的排放。利用测得的线性极化，我们将喷出物中纠缠磁场的相干尺度限制在θB <$10 −3弧度的角度大小，而极化角的旋转排除了喷流中大尺度有序轴对称磁场的存在，特别是大尺度环向场。
We present Atacama Large Millimeter/submillimeter Array 97.5 GHz total intensity and linear polarization observations of the mm-band afterglow of GRB 190114C spanning 2.2–5.2 hr after the burst. We detect linear polarization at the ≈5σ level, decreasing from Π = (0.87 ± 0.13)% to (0.60 ± 0.19)%, and evolving in polarization position angle from (10 ± 5)° to (−44 ± 12)° during the course of the observations. This represents the first detection and measurement of the temporal evolution of polarized radio/millimeter emission in a γ-ray burst. We show that the optical and X-ray observations between 0.03 days and ∼0.3 days are consistent with a fast-cooling forward shock expanding into a wind environment. However, the optical observations at ≲0.03 days, as well as the radio and millimeter observations, arise from a separate component, which we interpret as emission from the reverse-shocked ejecta. Using the measured linear polarization, we constrain the coherence scale of tangled magnetic fields in the ejecta to an angular size of θB ≈ 10−3 radian, while the rotation of the polarization angle rules out the presence of large-scale, ordered axisymmetric magnetic fields, and in particular a large-scale toroidal field, in the jet.