标题： 塞弗斯A HW2中6.7 GHz甲醇脉泽发射的重复耀斑的发现 显示英文标题

标题： Discovery of recurrent flares of 6.7 GHz methanol maser emission in Cepheus A HW2

摘要： 上下文：6.7 GHz的II类甲醇脉泽靠近大质量年轻恒星物体（HMYSOs）。 它们对局部条件变化的高度敏感性使它们成为新兴大质量恒星活动的有用标志。 目标：我们旨在使用新的和存档的单天线和高分辨率甚长基线干涉测量（VLBI）数据集，仔细检查Cep A HW2中6.7 GHz甲醇脉泽的变异性。 方法：我们使用Torun 32米射电望远镜在2009年至2021年间对目标方向的6.7 GHz甲醇脉泽进行了监测，并分析了在过去16年中获得的九个VLBI观测数据集。 结果：位于假定中心恒星位置附近且与射电喷流一致的微弱、极端红移脉泽发射显示出周期约为5年的爆发活动。爆发具有不对称的轮廓，上升时间与衰减时间比为0.18，相对振幅高于10。 爆发云团的速度在约11.5年的监测期间以3-4 * 10^-5 km/s/d的速度漂移。 两个爆发特征峰值之间的时滞表明激发因素的传播速度约为1000 km/s。 蓝移和红移特征流量密度的同步反相关变化在极端红移发射爆发后约2.5年开始。 显示英文摘要

摘要： 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.