Survival probability and energy modification of hydrogen energetic neutral atoms on their way from the termination shock to Earth orbit
Survival probability and energy modification of hydrogen energetic neutral atoms on their way from the termination shock to Earth orbit
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氢高能中性原子从终止激波到地球轨道途中的生存概率和能量修正
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
M. Bzowski
中科院分区：
文献类型：
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作者：
M. Bzowski
语境。鉴于 NASA SMEX 任务 IBEX 即将发射，识别高能中性原子 (ENA) 从诞生地到地球轨道的传输已成为一个重要问题，该任务致力于通过原位检测 ENA 对日光层界面进行成像。目标。我们研究了 IBEX (0.01-6 keV) 可检测到的氢 ENA (H ENA) 在终止激波和地球轨道之间的生存概率能量的变化。我们考虑了可变的、各向异性的太阳风以及太阳 EUV 辐射的影响。方法。原子的能量变化是通过对距太阳和地球轨道约 100 个天文单位之间的 H ENA 轨道进行数值模拟来计算的，同时考虑到太阳引力和莱曼辐射压力，该压力随时间变化并取决于原子的径向速度。为了计算原子对抗电离的生存概率，构建了一个详细的基于观测的 3D 和时间相关的 HENA 电离模型，并使用该模型，通过沿先前计算的轨道进行数值积分来计算原子的生存概率。结果。由于辐射压力，在太阳活动高度活跃期间，除了能量低于 0.1 keV 的原子外，H ENA 到达地球轨道时几乎没有能量和方向变化。 H ENA 的生存概率从太阳极小期可检测到的最慢 ENA 的 2% 增加到最快 ENA 的 80%。对于地球轨道上给定的能量，我们预计生存概率的波动幅度在 0.01 keV 的 20% 到 6 keV 的百分之几之间，并且生存概率的调制是地球轨道位置、到达方向的黄道纬度和太阳周期相位的函数，太阳极小期 0.1 keV 原子的振幅为百分之几十，而 6 keV 原子的振幅为百分之几。 太阳最大值。结论。通过适当考虑局部传输效应，IBEX 应该能够发现来自日光层界面的 H ENA 通量的对称性偏差有几个百分点。
Context. Recognizing the transport of Energetic Neutral Atoms (ENA), from their place of birth to Earth orbit, has become an important issue in light of the forthcoming launch of the NASA SMEX mission IBEX, which is devoted to imaging of the heliospheric interface by in-situ detection of ENAs. Aims. We investigate the modifications of both energy of survival probability of the hydrogen ENA (H ENA) detectable by IBEX (0.01-6 keV), between the termination shock and Earth orbit. We take into account the influence of the variable and anisotropic solar wind and of solar EUV radiation. Methods. Energy changes of the atoms are calculated by numerical simulations of the orbits of H ENA between ∼100 AU from the Sun and Earth orbit, taking into account solar gravity and Lyman-a radiation pressure, which is variable in time and depends on the radial velocity of the atom. To calculate the survival probabilities of the atoms against ionization, a detailed observation-based 3D and time-dependent model of H ENA ionization is constructed, and with the use of this model the probabilities of survival of the atoms are calculated by numerical integration along the previously-calculated orbits. Results. Due to radiation pressure, H ENA reach the Earth orbit practically without energy and direction change, apart from the atoms of energy lower than 0.1 keV, during high solar activity. The survival probability of H ENA increases from just ∼2% for the slowest detectable ENA at solar minimum to ∼80% for the fastest ENA. For a given energy at Earth orbit we expect fluctuations in the survival probability of amplitude between ∼20 percent at 0.01 keV to just a few percent at 6 keV and a modulation of survival probability as a function of the location at Earth orbit, ecliptic latitude of the arrival direction, and phase of solar cycle with an amplitude of a few dozen percent for 0.1 keV atoms at solar minimum to a few percent for 6 keV atoms at solar maximum. Conclusions. With appropriate account of local transport effects IBEX should be able to discover departures from symmetry in the flux of H ENA from the heliospheric interface at a level of a few percent.