AI 中文总结
研究通过对甲烷矮星双星的射电观测，利用其射电频谱截止测量磁场强度。结果发现基于能量平衡的标度律预测过高，基于洛伦兹 - 科里奥利力平衡的标度律与之相符，强调多频率监测对确定场产生标度律的重要性。
AI 中文摘要
褐矮星和气态巨行星预计通过其磁层中非热电子驱动的电子回旋脉泽不稳定性（ECMI）机制发射相干射电辐射。检测其回旋辐射中的特征频谱截止可能是测量其磁场强度的唯一可行途径。先前对一些冷褐矮星（光谱类型T或甲烷矮星）的射电测量在高达$\gtrsim 10\,{\rm GHz}$的频率下未显示出这样的截止，这意味着磁场强度远高于发电机标度律的典型预期。但高频辐射也可能并非源自大规模磁场，而是来自表面的小的高场强环，而标度律并未设计用于预测这些。本文展示了对一个甲烷矮星双星（WISEP J101905.63+652954.2）的射电观测，其射电辐射首次在无目标低频巡天中被检测到，更有可能该辐射追踪了该天体的大规模磁场。该天体的光谱显示出清晰的射电频谱截止，其位置得出极表面场强约为126高斯。基于能量平衡的典型发电机标度律现在对该天体的场强预测过高，但基于洛伦兹 - 科里奥利力平衡（埃尔萨瑟数规则）的标度律与测量结果一致。我们的结果表明，对褐矮星电子回旋脉泽辐射进行多频率（MHz到GHz）监测对于分别测量大尺度上的‘平均场’和较小空间尺度上的‘波动场’至关重要，以便确定最准确预测气态巨行星和冷褐矮星金属氢层中场产生的发电机标度律。
英文摘要
Brown dwarfs and gas-giant planets are expected to emit coherent radio emission via the electron cyclotron maser instability (ECMI) mechanism powered by non-thermal electrons in their magnetospheres. Detection of a characteristic spectral cutoff in their cyclotron emission is likely to be the only feasible route to measure their magnetic field strengths. Previous radio measurements of a subset of cold brown dwarfs (spectral type T or methane dwarfs) have not shown such a cutoff at frequencies as high as $\gtrsim 10\,{\rm GHz}$, implying field strengths far higher than canonical expectations from dynamo scaling laws. However, it is also possible that these high-frequency emissions did not originate in the large-scale magnetic field but rather from small high-field-strength loops at the surface, which the scaling laws are not designed to predict. Here we present radio observations of a methane dwarf binary (WISEP J101905.63+652954.2) whose radio emission was first detected in an untargeted low-frequency survey, making it more likely that the emission traces the object's large-scale magnetic field. The object's spectrum shows a clear radio spectral cutoff whose location yields a polar surface field strength of around 126 gauss. Canonical dynamo scaling laws based on energy balance now over-predict the field strength for this object, but the scaling law based on Lorentz-Coriolis force balance (Elsasser number rule) is consistent with the measurement. Our results suggest that multi-frequency (MHz to GHz) monitoring of brown-dwarf electron cyclotron maser emission is essential to separately measure the `mean field' on large scales and `fluctuating' fields on smaller spatial scales in order to determine the dynamo scaling law that most accurately predicts field generation in the metallic hydrogen layer of gas giants and cold brown dwarfs.
Comments10 pages, 4 figures, 3 tables. Accepted for publication in A&A
