论文标题
伽马射线外部冲击中磁场几何形状的极化约束
Polarization constraints on the geometry of the magnetic field in the external shock of gamma-ray bursts
论文作者
论文摘要
我们研究了长期伽马射线爆发的光学余波中线性极化测量的合奏。我们假设非侧向式的顶级射流几何形状，并在假设它们代表统计上无偏见的假设下使用相对较大的测量值。这使我们能够约束最大预测极化与测量的比率，这是外部冲击下游区域中磁场几何形状的指标。我们发现，对于完全有序的磁场，与冲击法线平行的完全有序的磁场或完全包含在冲击平面中的磁场相对于最大值的最大值被基本抑制。测得的极化平均限制在理论上可能的最大值的25％至30％之间。这种还原要求磁场的垂直成分相对于平行于冲击阵线的分量，在能量中占主导地位，这对于产生的冲击和/或冲击压缩场所期望的。但是，我们发现数据仅在略微支持一个简单的顶帽射流的假设上，指向流出的几何形状。
We study the ensemble of linear polarization measurement in the optical afterglows of long-duration gamma-ray bursts. We assume a non sideways-expanding top-hat jet geometry and use the relatively large number of measurements under the assumption that they represent a statistically unbiased sample. This allows us to constrain the ratio between the maximum predicted polarization and the measured one, which is an indicator of the geometry of the magnetic field in the downstream region of the external shock. We find that the measured polarization is substantially suppressed with respect to the maximum possible for either a completely ordered magnetic field parallel to the shock normal or to a field that is entirely contained in the shock plane. The measured polarization is limited, on average, to between 25 and 30% of the maximum theoretically possible value. This reduction requires the perpendicular component of the magnetic field to be dominant in energy with respect to the component parallel to the shock front, as expected for a shock generated and/or shock compressed field. We find, however, that the data only marginally support the assumption of a simple top-hat jet, pointing towards a more complex geometry for the outflow.
