活动星特殊的射电$-$ X射线关系
Peculiar radio$-$X-ray relationship in active stars
摘要：
非热的5 GHz射电光度和活动恒星日冕的软X射线光度之间的经验关系，被称为Güdel-Benz关系（Güdel & Benz 1993），一直是恒星射电天文学的基石，因为它明确地将射电发射与日冕加热机制联系起来。这种关系从太阳上的微耀斑延伸到最活跃的恒星的日冕，表明活跃的日冕是通过类似耀斑的过程加热的（Benz & Güdel 1994）。这种关系被认为起源于一个一致的分区的可用耀斑能量到相对论性收费，通过非相干回旋同步加速器机制，并在无线电波段发射的散装日冕等离子体的加热，通过韧致辐射机制发射的X射线带。因此，来自恒星和亚恒星物体的相干发射预计不会像在超冷矮星和棕矮星中观察到的那样遵循这种经验关系。在这里，我们报告了一群无线电检测到的色球活跃恒星，尽管它们的无线电发射因其高圆极化分数和高亮度温度而被归类为相干发射，但它们令人惊讶地遵循居德尔-本茨关系。我们的研究结果促使重新审视Güdel-Benz关系背后的物理学，它对活跃恒星中日冕加热和粒子加速机制的影响，以及太阳和恒星耀斑之间的现象学联系。
英文摘要：
The empirical relationship between the non-thermal 5GHz radio luminosity and the soft X-ray luminosity of active stellar coronae, canonically called the Güdel-Benz relationship (Güdel & Benz 1993), has been a cornerstone of stellar radio astronomy as it explicitly ties the radio emission to the coronal heating mechanisms. The relationship extends from microflares on the Sun to the coronae of the most active stars suggesting that active coronae are heated by a flare-like process (Benz & Güdel 1994). The relationship is thought to originate from a consistent partition of the available flare energy into relativistic charges, that emit in the radio-band via the incoherent gyrosynchrotron mechanism, and heating of the bulk coronal plasma, that emits in the X-ray band via the Bremsstrahlung mechanism. Consequently, coherent emission from stellar and sub-stellar objects is not expected to adhere to this empirical relationship, as is observed in ultracool dwarf stars and brown dwarfs. Here we report a population of radio-detected chromospherically active stars that surprisingly follows the Güdel-Benz relationship despite their radio emission being classified as coherent emission by virtue of its high circularly polarised fraction and high brightness temperature. Our results prompt a re-examination of the physics behind the Güdel-Benz relationship, its implication for the mechanism of coronal heating and particle acceleration in active stars and the phenomenological connection between solar and stellar flares.
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