Energetic proton back-precipitation onto the solar atmosphere in relation to long-duration gamma-ray flares
Energetic proton back-precipitation onto the solar atmosphere in relation to long-duration gamma-ray flares
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与长持续时间伽马射线耀斑相关的太阳大气中的高能质子反沉淀
DOI：
10.1051/0004-6361/202142002
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发表时间：
2022
影响因子：
6.5
通讯作者：
Hutchinson A
中科院分区：
文献类型：
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作者：
Hutchinson A
长持续时间伽马射线耀斑 (LDGRF) 事件期间的伽马射线发射被认为主要是由大于 300 MeV 的质子与光球层或光球层附近的环境等离子体相互作用引起的。长时间的伽马射线发射促使人们提出这样的建议：高能质子的来源是日冕物质抛射（CME）驱动的激波中的加速，随后粒子在较长时间内反向沉淀到太阳大气中。目的我们使用测试粒子模拟来研究后一种假设，这使我们能够研究与湍流相关的散射是否有助于粒子克服磁镜效应，磁镜在粒子行进时通过反射粒子来阻碍反向沉淀方法研究瞬时沉淀分数 P，即在固定高度 ri 成功沉淀注入的质子比例，作为散射平均自由程 λandri 的函数。在中等散射条件下（λ = 0.1 AU），计算了 8 个 LDGRF 事件的总降水分数上限。结果我们发现，与无散射情况相比，散射的存在有助于反降水，尽管在非常低的 λ 值下，太阳风的向外对流最终占主导地位。对于八个 LDGRF 事件，由于强镜像，即使在存在散射的情况下，也非常小，在 0.56% 到 0.93% 之间。 结论 根据我们的模拟，如观测结果所示，对于移动激波源来说，时间延长的加速度和大的总降水分数无法协调一致。因此，在这种情况下不可能同时获得长持续时间的γ射线发射和高效降水。这些结果对日冕物质抛射冲击源情景作为 LDGRF 中 γ 射线产生的主要机制提出了挑战。
ContextGamma-ray emission during long-duration gamma-ray flare (LDGRF) events is thought to be caused mainly by > 300 MeV protons interacting with the ambient plasma at or near the photosphere. Prolonged periods of the gamma-ray emission have prompted the suggestion that the source of the energetic protons is acceleration at a coronal mass ejection (CME)-driven shock, followed by particle back-precipitation onto the solar atmosphere over extended times.AimsWe study the latter hypothesis using test particle simulations, which allow us to investigate whether scattering associated with turbulence aids particles in overcoming the effect of magnetic mirroring, which impedes back-precipitation by reflecting particles as they travel sunwards.MethodsThe instantaneous precipitation fraction,P, the proportion of protons that successfully precipitate for injection at a fixed height,ri, is studied as a function of scattering mean free path,λandri. Upper limits to the total precipitation fraction, , were calculated for eight LDGRF events for moderate scattering conditions (λ= 0.1 AU).ResultsWe find that the presence of scattering helps back-precipitation compared to the scatter-free case, although at very lowλvalues outward convection with the solar wind ultimately dominates. For eight LDGRF events, due to strong mirroring, is very small, between 0.56 and 0.93% even in the presence of scattering.ConclusionsTime-extended acceleration and large total precipitation fractions, as seen in the observations, cannot be reconciled for a moving shock source according to our simulations. Therefore, it is not possible to obtain both long durationγray emission and efficient precipitation within this scenario. These results challenge the CME shock source scenario as the main mechanism forγray production in LDGRFs.