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arXiv 0903.0716astro-ph.HE
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脉冲星同步加速器:相干射电辐射

The pulsar synchrotron: coherent radio emission

Ioannis Contopoulos

摘要:

我们提出了一个简单的物理图片的相干无线电发射的轴对称脉冲星磁层,这是完全不同的无线电发射来自磁极帽的典型范例的产生。在这第一篇论文中,我们只考虑轴对称的情况下,一个对齐的转子。我们的图片利用了磁层的MHD表示的一个重要元素,即共转闭合线区域(“死区”)和起源于极冠的开放场线之间的分界线。沿着分界线流动的返回电流对应于从极冠发出的主磁层电流。穿过分界线,磁场的环向分量和极向分量都不连续地变化。极向分量的不连续性要求存在一个显著的环形电流,而这一点至今尚未得到解释。我们估计了这个环形电流在闭合线区域尖端的位置和厚度,并表明它由与洛伦兹因子在10^5量级上共转的电子(正电子)组成,发射出非相干的同步辐射,在硬X射线中达到峰值。这些粒子停留在接近赤道的环形电流最高的区域,路径长度为一米。我们提出,在与该路径长度相当的波长处,粒子发射相干辐射,辐射功率与N^2成正比,其中N是上述路径长度中的粒子总数。我们计算了在这个波长范围内的总射电功率及其与脉冲星周期和恒星磁场的比例关系,并表明它与基于观测的射电光度估计是一致的。

英文摘要:

We propose a simple physical picture for the generation of coherent radio emission in the axisymmetric pulsar magnetosphere that is quite different from the canonical paradigm of radio emission coming from the magnetic polar caps. In this first paper we consider only the axisymmetric case of an aligned rotator. Our picture capitalizes on an important element of the MHD representation of the magnetosphere, namely the separatrix between the corotating closed-line region (the `dead zone') and the open field lines that originate in the polar caps. Along the separatrix flows the return current that corresponds to the main magnetospheric electric current emanating from the polar caps. Across the separatrix, both the toroidal and poloidal components of the magnetic field change discontinuously. The poloidal component discontinuity requires the presence of a significant annular electric current which has up to now been unaccounted for. We estimate the position and thickness of this annular current at the tip of the closed line region, and show that it consists of electrons (positrons) corotating with Lorentz factors on the order of 10^5, emitting incoherent synchrotron radiation that peaks in the hard X-rays. These particles stay in the region of highest annular current close to the equator for a path-length of the order of one meter. We propose that, at wavelengths comparable to that path-length, the particles emit coherent radiation, with radiated power proportional to N^2, where N is the population of particles in the above path-length. We calculate the total radio power in this wavelength regime and its scaling with pulsar period and stellar magnetic field and show that it is consistent with estimates of radio luminosity based on observations.

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