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首页> 外文期刊>The Astrophysical journal >ROTATIONAL MODULATION OF THE RADIO EMISSION FROM THE M9 DWARF TVLM 513-46546: BROADBAND COHERENT EMISSION AT THE SUBSTELLAR BOUNDARY?
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ROTATIONAL MODULATION OF THE RADIO EMISSION FROM THE M9 DWARF TVLM 513-46546: BROADBAND COHERENT EMISSION AT THE SUBSTELLAR BOUNDARY?

机译：M9 DWARF TVLM 513-46546的无线电发射的旋转调制：子边界的宽带宽带相干发射？

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摘要

The Very Large Array was used to observe the ultracool rapidly rotating M9 dwarf TVLM 513—46546 simultaneously at 4.88 and 8.44 GHz. The radio emission was determined to be persistent, variable, and periodic at both frequencies with a period of ～2 hr. This periodicity is in excellent agreement with the estimated period of rotation of the dwarf based on its v sin i of ～60 km s~(-1). This rotational modulation places strong constraints on the source size of the radio-emitting region and hence the brightness temperature of the associated emission. We find the resulting high brightness temperature, together with the inherent directivity of the rotationally modulated component of the emission, difficult to reconcile with incoherent gyrosynchrotron radiation. We conclude that a more likely source is coherent, electron cyclotron maser emission from the low-density regions above the magnetic poles. This model requires the magnetic field of TVLM 513 —46546 to take the form of a large-scale, stable dipole or multipole with surface field strengths up to at least 3 kG. We discuss a mechanism by which broadband, persistent electron cyclotron maser emission can be sustained in the low-density regions of the magnetospheres of ultracool dwarfs. A second nonvarying, unpo-larized component of the emission may be due to depolarization of the coherent electron cyclotron maser emission or, alternatively, incoherent gyrosynchrotron or synchrotron radiation from a population of electrons trapped in the large-scale magnetic field.
机译：超大阵列用于同时观测4.88 GHz和8.44 GHz超冷快速旋转的M9矮TVLM 513-46546。在这两个频率下，无线电发射被确定为持续，可变和周期性的，周期约为2小时。这个周期与基于60 km s〜（-1）的v sin i估计的矮星自转周期非常吻合。这种旋转调制对无线电发射区域的源尺寸以及因此的相关发射的亮度温度施加了严格的约束。我们发现产生的高亮度温度，以及发射的旋转调制分量的固有方向性，很难与非相干陀螺回旋加速器辐射调和。我们得出结论，更可能的源是来自磁极上方低密度区域的相干电子回旋加速器maser发射。该模型要求TVLM 513 —46546的磁场采取表面场强至少达到3 kG的大规模，稳定的偶极子或多极子的形式。我们讨论了一种机制，通过该机制，可以在超冷矮星的磁层的低密度区域中维持持续的持续的电子回旋加速器maser发射。发射的第二个不变的，非极化的分量可能是由于相干电子回旋加速器主辐射的去极化，或者是由于来自大磁场中捕获的大量电子的非相干陀螺回旋加速器或同步加速器辐射引起的。

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