超冷矮星的稳态和瞬态射电辐射
Steady and Transient Radio Emission from Ultracool Dwarfs
摘要：
我们在超冷矮双星LP 349- 25的另外两个时期检测到无线电发射，发现所观察到的发射在10秒和10.7小时之间的时间尺度上是宽带和稳定的，以及在0.6和1.6年的时间尺度上。这个系统对于具有可检测到的无线电发射的超冷矮星来说是不寻常的，因为它缺乏任何大尺度的变化，特别是其他具有可检测到的无线电发射水平的物体所表现出的爆发（周期性或非周期性）行为。我们探讨的限制，缺乏变化的长期和短期的时间尺度，平坦的光谱指数，意味着有关的无线电发射结构和机制。时间上的限制，主张高纬度发射区的大倾角，使它总是在视图中，并生存至少0.6年。时间约束也限制了等离子体的条件，这意味着电子密度n_e <4 × 10^5 cm-3，B < 130 G，这样就不会看到由于高能粒子的碰撞或辐射损失而引起的时间变化。他们提供的意见和约束条件是最兼容的非热无线电发射机制，可能回旋同步辐射从空间均匀或不均匀的源。这表明，类似于在超冷矮星的色球、过渡区和日冕等离子体中观察到的行为，在活跃的高质量恒星中观察到的磁活动模式可以存活到亚恒星边界。我们还介绍了超冷矮星2 MASS 05233822-140322和2 MASS 14563831 -2809473（=LHS 3003）的多频射电观测的新纪元;每一个都在至少一个以前的纪元中被探测到，但在这里报告的纪元中没有被探测到。
英文摘要：
We detect radio emission in an additional two epochs of the ultracool dwarf binary LP 349- 25, finding that the observed emission is broadband and steady on timescales between 10s and 10.7 hours, as well as on timescales of 0.6 and 1.6 years. This system is unusual for ultracool dwarfs with detectable radio emission, in exhibiting a lack of any large scale variability, particularly the bursting (periodic or aperiodic) behavior exhibited by the other objects with detectable levels of radio emission. We explore the constraints that the lack of variability on long and short timescales, and flat spectral index, imply about the radio-emitting structures and mechanism. The temporal constraints argue for a high latitude emitting region with a large inclination so that it is always in view, and survives for at least 0.6 year. Temporal constraints also limit the plasma conditions, implying that the electron density be n_e <4x10^5 cm-3 and B < 130 G in order not to see time variations due to collisional or radiative losses from high energy particles. The observations and constraints provided by them are most compatible with a nonthermal radio emission mechanism, likely gyrosynchrotron emission from a spatially homogeneous or inhomogeneous source. This indicates that, similar to behaviors noted for chromospheric, transition region, and coronal plasmas in ultracool dwarfs, the magnetic activity patterns observed in active higher mass stars can survive to the substellar boundary. We also present new epochs of multi-frequency radio observations for the the ultracool dwarfs 2MASS 05233822-140322 and 2MASS14563831-2809473(=LHS 3003); each has been detected in at least one previous epoch but are not detected in the epochs reported here.
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