发表机构
Indian Institute of Astrophysics（印度天体物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
利用低频热韧致辐射的圆偏振观测，通过射线追踪模拟估算日冕磁场强度，在51 MHz下测得峰值圆偏振度约2.7%，对应磁场约1.55高斯。
AI 中文摘要
利用瞬变射电暴以外的观测手段，测量日心距离 $r\\,{\gtrsim}\\,1.1\\,R_{\odot}$ 处太阳日冕磁场强度的研究十分罕见。频率低于 100 MHz 的热韧致辐射射电辐射通常起源于太阳日冕中 $r\\,{>}\\,1.1R_{\odot}$ 的区域，其圆偏振观测可有效用于此目的。热韧致辐射本身是随机偏振的，但在磁场存在时，它会在两种偏振方向相反的圆偏振模式中传播，这两种模式在介质中的差分吸收会导致可观测的圆偏振。我们报告了一项利用 Gauribidanur 射电日像仪（GRAPH）在 51 MHz 频率下对太阳日冕上述圆偏振进行二维成像观测的案例研究，并估算了相关的日冕磁场强度。根据 GRAPH 观测到的总强度和圆偏振强度图像计算得到的峰值圆偏振度（$dcp$）约为 2.7%。利用射线追踪模拟，我们发现观测到的峰值 $dcp$ 对应于 51 MHz 下位于 $r\\,{\approx}\\,1.65\\,{\pm}\\,0.15\\,R_{\odot}$ 处的射电源，其磁场强度约为 $1.55\\,{\pm}\\,0.3$ 高斯。
英文摘要
Measurements of the magnetic field strength in the solar corona at heliocentric distances $r\,{\gtrsim}\,1.1\,R_{\odot}$, using observations other than transient radio bursts, are rare. Circular polarization observations of thermal bremsstrahlung radio emission at frequencies $<$ 100 MHz, which typically originate at $r\,{>}\,1.1R_{\odot}$ in the solar corona, can be effectively used for this purpose. The thermal bremsstrahlung emission is randomly polarized, but in the presence of a magnetic field it propagates in two oppositely polarized circular modes whose differential absorption in the medium results in an observable circular polarization. We report a case study of two-dimensional imaging observations of the above mentioned circular polarization in the solar corona at 51\,MHz using the Gauribidanur RAdioheliograPH (GRAPH), and estimates of the associated coronal magnetic field strength. The peak degree of circular polarization ($dcp$), calculated from the observed total and circularly polarized intensity images with the GRAPH, is ${\approx}$2.7%. Using ray-tracing simulations we find that the observed peak $dcp$ corresponds to a radio source located at $r\,{\approx}\,1.65\,{\pm}\,0.15\,R_{\odot}$ at 51 MHz, and its field strength is ${\approx}\,1.55\,{\pm}\,0.3\,$Gauss.
CommentsAccepted in The Astrophysical Journal
