The sources of widespread solar energetic particle events - A comprehensive combined modeling and observational approach

太阳高能粒子(SEP)通过太阳的磁重联过程和/或激波来加速。这些SEP事件中的一个子群是所谓的广泛事件，它显示了粒子在日光层中极大的纵向扩散，最高可达360度。由于它们的粒子分布很广，与太阳的母体活动区相隔很远，这些事件在空间天气方面特别令人感兴趣，需要确定潜在的过程。不同的机制正在讨论中：一方面，粒子的传输，即粒子向外传播过程中的强烈垂直扩散可能是造成较大扩散的原因。另一方面，粒子进入行星际介质的开放磁场区域的大注入区域，例如大范围，可能是原因。如此大的注入区域可以指向特定的磁场配置，然而，也可以使用更大的加速区域，如激波。由于大型SEP事件通常不仅显示太阳耀斑，而且还伴随着日冕物质抛射(CME)，这可以驱动激波，因此除了点状耀斑区域外，可能还存在如此大的加速区。SEP事件的现场测量由一组航天器记录，例如位于地球轨道上。为了推断加速和注入过程，采用了多波长遥感观测。为了弥合注射位置和现场测量之间的差距，采用了描述颗粒传播的输运模型。由于每个SEP事件分别由加速、注入和传输过程的相互作用决定，因此需要进行全面和综合的分析，以理清不同的成分，并确定极大颗粒扩散的驱动因素。在拟议的研究中，我们将侧重于在1AU同时靠近地球以及在两个立体航天器上观测到的近相对论的广泛电子事件。我们将使用最先进的传输模型来再现多个航天器对特定大范围事件的观测。通过采用观察和建模相结合的方法，我们将确定每个分析事件的广泛分布的主要驱动因素。此外，我们还研究了点源和强垂直输运是否可以解释这些观测，或者是否所有这些极端事件都需要一定宽度的注入区。最后，我们将分析是否存在不同类型的广泛事件，或者总是必须涉及某些过程的组合。

Solar Energetic Particle (SEP) are accelerated by magnetic reconnection processes at the Sun and/or by shocks. A subgroup of these SEP events are the so-called widespread events which show extremely wide longitudinal particle spreads in the heliosphere up to 360 degrees. Because of their wide particle distributions, up to longitudes far separated from the parent activity regions at the Sun, these events are of special interest in terms of space weather and the underlying processes need to be identified. Different mechanisms are under discussion: On the one hand, the particle transport, i.e. strong perpendicular diffusion during the outward propagation of the particles may be responsible for the wide spreads. On the other hand, a large injection region, e.g. a wide range, over which the particles enter the open magnetic field regime of the interplanetary medium, could be the reason. Such a large injection region could point to specific magnetic field configurations, however, a larger acceleration region such as a shock would serve as well. As large SEP events often show not only a solar flare but also an accompanying Coronal Mass Ejection (CME), which can drive a shock, such a large acceleration region, apart from the point-like flaring region, might be present. In-situ measurements of SEP events are recorded by a fleet of spacecraft, e.g. situated in the Earth's orbit. To infer the acceleration and injection processes, multi-wavelength remote-sensing observations are employed. To bridge the gap between the injection sites and the in-situ measurements, transport models are used which characterize the particle propagation. As each SEP event is determined by the interplay of acceleration, injection, and transport processes, respectively, a comprehensive and combined analysis is needed to disentangle the different ingredients and to identify the drivers of the extraordinary wide particle spreads. In the proposed study we will focus on near-relativistic widespread electron events observed at 1 AU simultaneously close to Earth as well as at the two STEREO spacecraft. We will use a state of the art transport model to reproduce the multi-spacecraft observations of specific widespread events. By employing a combined observational and modeling approach we will identify the main drivers of the wide spreads for each analyzed event. Furthermore, we investigate if a point source together with strong perpendicular transport can explain such observations or if a certain width of the injection region is needed for all of these extreme events. Finally, we will analyze if different types of widespread events exist or if always a combination of certain processes must be involved.