电子回旋脉泽不稳定性驱动的太阳射电辐射机制

Solar Radio Emission Mechanism Driven by Electron-cyclotron Maser Instability

在解释天体爆发过程中的短时标相干射电辐射现象方面,非热电子驱动的回旋脉泽辐射得到了广泛应用。在以往的研究中,一个关键条件是非热电子具有各向异性速度分布,从而有效激发回旋脉泽不稳定性。然而,观测显示太阳和其他天体的非热电子经常呈现负幂律谱形式的能量分布。非热电子的这种负幂律能谱特征会严重抑制回旋脉泽不稳定性放大率,因此,进一步研究非热电子的负幂律能谱分布行为,能拓宽电子回旋脉泽辐射机制的适用性,很好地发展天体射电辐射机制理论。最近研究结果显示,负幂律谱电子的低能截止行为可以有效地激发电子回旋脉泽辐射,从而拓宽了其在天体物理研究中的应用范围。

Electromagnetic radiation mechanism is the most basic and important research topic in astrophysics.And the generation of radio emission is one of the most complex emission mechanisms. This paper gives an overview of the solar radio emission and bursts from observation to theory.The electron-cyclotron maser instability is an important mechanism that directly amplifies electromagnetic radiation by nonthermal energetic electrons trapped in magnetic fields.It has been extensively applied to explain various short-time radio burst phenomena,such as the auroral kilometric radiation from the Earth,radio emission from other magnetized planets in the solar system and extra-solar planets,radio bursts or spikes from the Sun and other stars.Most discussions on the electron-cyclotron maser instability suppose that the nonthermal electrons have an anisotropy loss-cone distribution.This is the primary condition of the nonthermal electrons to driven electron-cyclotron maser instability and it restrict this mechanism to be applied widely. On the other hand,major astrophysical observations imply that the nonthermal electrons frequently exhibit an energy distribution that can be approximated by a negative power-law spectrum with a lower energy cutoff.From the close connection between the hard X ray emission and radio emission we can expect that the hard X ray and radio emission are driven by the same nonthermal electron beam.Recent study show that the power-law electrons with the steepness cutoff can efficiently excite the electron-cyclotron maser instability because of the energy reverse distribution below the cutoff energy.Thus greatly broaden the applicable condition of the electron cyclotron maser emission mechanism,and then expand the prospect of application of it in astrophysics.