GRB 061121在其X射线浅衰变相附近的光学行为
Optical Behavior of GRB 061121 around its X-Ray Shallow Decay Phase
摘要：
目标。我们报告的详细研究的光学余辉的GRB 061121与我们原来的时间序列测光数据。结合X射线观测，讨论了它的光学余辉和X射线余辉的来源。方法.我们用东广岛天文台的Kanata 1.5-m望远镜观测了雨燕暴GRB 061121的光学余辉。我们的观察涵盖了X射线平台期之后的一段时间。我们还在2010年用斯巴鲁望远镜进行了深度成像，以估计宿主星系的污染。结果在光变曲线中，我们发现光学余辉也表现出与X射线余辉一样的突变。然而，我们的观察表明，在光变曲线中的光学断裂之前可能存在一个驼峰结构或平坦期。在X射线光变曲线中没有这样一个隆起的迹象。结论.这意味着光学的发射区域与X射线的发射区域不同。光学光变曲线中的驼峰可能是由另一个与早期余辉不同的前向激波的同步辐射的典型频率通过引起的。所观察到的衰变和光谱指数与标准的同步辐射激波模型不一致。因此，观察需要在冲击区的微物理参数的变化或中央引擎的先前活动。或者，在浅衰变阶段的发射可能是两个前向冲击发射的组合，如光变曲线中的驼峰结构所示。
英文摘要：
Aims. We report on a detailed study of the optical afterglow of GRB 061121 with our original time-series photometric data. In conjunction with X-ray observations, we discuss the origin of its optical and X-ray afterglows. Methods. We observed the optical afterglow of Swift burst GRB 061121 with the Kanata 1.5-m telescope at Higashi-Hiroshima Observatory. Our observation covers a period just after an X-ray plateau phase. We also performed deep imaging with the Subaru telescope in 2010 in order to estimate the contamination of the host galaxy. Results. In the light curve, we find that the optical afterglow also exhibited a break as in the X-ray afterglow. However, our observation suggests a possible hump structure or a flattening period before the optical break in the light curve. There is no sign of such a hump in the X-ray light curve. Conclusions. This implies that the emitting region of optical was distinct from that of X-rays. The hump in the optical light curve was possibly caused by the passage of the typical frequency of synchrotron emission from another forward shock distinct from the early afterglow. The observed decay and spectral indices are inconsistent with the standard synchrotron-shock model. Hence, the observation requires a change in microphysical parameters in the shock region or a prior activity of the central engine. Alternatively, the emission during the shallow decay phase may be a composition of two forward shock emissions, as indicated by the hump structure in the light curve.
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