We followed-up the massive young stellar object (MYSO) S255-NIRS3 (=S255-IRS1b) during its recent accretion outburst event in the Ks band with Kanata/HONIR for four years after its burst and obtained a long-term light curve. This is the most complete NIR light-curve of the S255-NIRS3 burst event that has ever been presented. The light curve showed a steep increase reaching a peak flux that was 3.4 mag brighter than the quiescent phase and then a relatively moderate year-scale fading until the last observation, similar to that of the accretion burst events such as EXors found in lower-mass young stellar objects. The behavior of the Ks band light curve is similar to that observed in 6.7 GHz class II methanol maser emission, with a sudden increase followed by moderate year-scale fading. However, the maser emission peaks appear 30-50 days earlier than that of the Ks band emission. The similarities confirmed that the origins of the maser emission and the Ks band continuum emission is common as previously shown from another infrared and radio observations by Stecklum et al. (2016); Caratti o Garatti et al. (2017a); Moscadelli et al. (2017). However, the differences in energy transfer paths, such as the exciting/emitting/scattering structures, may cause the delay in the flux-peak dates.

中文翻译：

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大质量年轻星体S255-NIRS3吸积爆发的近红外监测

我们对大质量年轻恒星天体（MYSO）S255-NIRS3（=S255-IRS1b）最近在Ks波段的吸积爆发事件中与Kanata/HONIR一起在其爆发后的四年中进行了跟踪，并获得了长期的光变曲线。这是有史以来最完整的 S255-NIRS3 爆发事件的 NIR 光曲线。光变曲线显示出急剧增加，达到比静止阶段亮 3.4 mag 的峰值通量，然后相对温和的年尺度衰减直到最后一次观测，类似于吸积爆发事件，例如在低质量中发现的 EXor年轻的恒星。Ks 波段光曲线的行为类似于在 6.7 GHz II 类甲醇脉泽发射中观察到的行为，突然增加，然后是中等的年尺度衰减。然而，脉泽发射峰值比 Ks 波段发射提前 30-50 天出现。相似之处证实了微波激射发射和 Ks 波段连续谱发射的起源是常见的，如先前 Stecklum 等人在另一项红外和无线电观测中所示。(2016); Caratti o Garatti 等人。(2017a); 莫斯卡德利等。(2017)。然而，能量传输路径的差异，例如激发/发射/散射结构，可能会导致通量峰值日期的延迟。