恒星诞生时磁活动的证据：来自0级原恒星HOPS 383的强大X射线耀斑
Evidence for magnetic activity at starbirth: a powerful X-ray flare from the Class 0 protostar HOPS 383
摘要：
上下文0级原恒星代表太阳型恒星的最早演化阶段，在此期间，系统的大部分质量都存在于一个由气体和尘埃组成的下沉包层中，而不是在中央的新生恒星中。虽然X射线是更演化的原恒星和年轻恒星中磁活动的关键特征，但这种磁活动是否存在于0级阶段仍然存在争议。目的。我们的目标是用X射线探测真正的0级原恒星。方法.我们在2017年12月用钱德拉X射线天文台（$\sim$ 84 ks）的X射线和南方天体物理研究望远镜的近红外成像观测了HOPS 383。结果HOPS 383是在一次强烈的耀斑期间被X射线探测到的。这个硬（E > 2 keV）X射线对应物与HOPS 383的西北4 cm分量在空间上一致，这将是HOPS 383发射的射电热喷流的基础。耀斑持续时间为$\sim$ 3.3小时;在峰值时，X射线亮度达到$\sim$ 4 x 1 E31 erg s -1，在2-8 keV的能量带，至少比HOPS 383未被检测到的静态发射大一个数量级。X射线耀斑光谱是高度吸收的（NH $\sim$ 7 x 1 E23 cm -2），它显示出6.4 keV的发射线，等效宽度为$\sim$ 1.1 keV，由中性或低电离铁产生。结论.从HOPS 383探测到的一个强大的X射线耀斑直接证明了在太阳型恒星的最早形成阶段可能存在磁活动。
英文摘要：
Context. Class 0 protostars represent the earliest evolutionary stage of solar-type stars, during which the majority of the system mass resides in an infalling envelope of gas and dust and is not yet in the central, nascent star. Although X-rays are a key signature of magnetic activity in more evolved protostars and young stars, whether such magnetic activity is present at the Class 0 stage is still debated. Aims. We aim to detect a bona fide Class 0 protostar in X-rays. Methods. We observed HOPS 383 in 2017 December in X-rays with the Chandra X-ray Observatory ($\sim$84 ks) and in near-infrared imaging with the Southern Astrophysical Research telescope. Results. HOPS 383 was detected in X-rays during a powerful flare. This hard (E > 2 keV) X-ray counterpart was spatially coincident with the northwest 4 cm component of HOPS 383, which would be the base of the radio thermal jet launched by HOPS 383. The flare duration was $\sim$3.3 h; at the peak, the X-ray luminosity reached $\sim$4 x 1E31 erg s --1 in the 2-8 keV energy band, a level at least an order of magnitude larger than that of the undetected quiescent emission from HOPS 383. The X-ray flare spectrum is highly absorbed (NH $\sim$ 7 x 1E23 cm --2), and it displays a 6.4 keV emission line with an equivalent width of $\sim$1.1 keV, arising from neutral or low-ionization iron. Conclusions. The detection of a powerful X-ray flare from HOPS 383 constitutes direct proof that magnetic activity can be present at the earliest formative stages of solar-type stars.
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