论文标题
发现Cepheus A HW2的6.7 GHz甲醇梅尔发射的复发耀斑
Discovery of recurrent flares of 6.7 GHz methanol maser emission in Cepheus A HW2
论文作者
论文摘要
上下文：6.7 GHz的II级甲醇泥浆果始于高质量的年轻恒星物体（Hmysos）。它们对局部条件变化的高灵敏度使它们成为新兴巨大恒星活性的有用标记。目的：我们旨在使用新的和档案的单词和高分辨率非常长的基线干涉法（VLBI）数据集仔细研究CEP A HW2中6.7 GHz甲醇masers的可变性。方法：我们使用Torun 32 M射电望远镜在2009年至2021年之间向目标监测了6.7 GHz甲醇masers，并分析了16年以上VLBI观察结果的9个数据集。结果：靠近假定的中心星位置附近的微弱，极端红移的maser发射，与无线电射流相吻合，表现出较小的活动，周期约为5年。耀斑具有不对称的轮廓，上升时间比为0.18，相对振幅高于10。耀斑的云层的速度以3-4 * 10^-5 km/s/d的速度漂移约11.5年。两个耀斑特征的峰之间的时置意味着令人兴奋的因子约1000 km/s的传播速度。在极端红移发射的耀斑之后，蓝色和红移特征的通量密度的同步和反相关的变化开始了约2.5年。
Context: Class II methanol masers at 6.7 GHz originate close to high-mass young stellar objects (HMYSOs). Their high sensitivity to local condition variations makes them a useful marker of the activity of the emerging massive stars. Aims: We aim to closely examine the variability of the 6.7 GHz methanol masers in Cep A HW2 using the new and archival single-dish and high-resolution Very-Long-Baseline Interferometry (VLBI) datasets. Methods: We monitored 6.7 GHz methanol masers towards the target between 2009 and 2021 using the Torun 32 m radio telescope, and analysed nine datasets of VLBI observations taken over 16 yr. Results: Faint, extremely redshifted maser emission located close to the presumed central star position and coincident with the radio jet shows flaring activity with a period of ~ 5 yr. Flares have an asymmetric profile with a rise-to-decay time ratio of 0.18 and relative amplitude higher than 10. The velocity of the flaring cloudlets drifts at a rate of 3-4 * 10^-5 km/s/d for about 11.5 yr of the monitoring. The time-lag between the peaks of the two flaring features implies a propagation speed of the exciting factor of ~ 1000 km/s. Synchronised and anticorrelated variations of the flux density of blue- and redshifted features begin ~ 2.5 yr after flares of the extremely redshifted emission.
