标题： X射线丰富的伽马暴050408的广泛多带研究。 一个可能的离轴事件，并伴有强烈的能量注入 显示英文标题

标题： Extensive multiband study of the X-ray rich GRB 050408. A likely off-axis event with an intense energy injection

摘要： 目标。 理解X射线丰富（XRR）暴 GRB 050408 的多波段光变曲线的形状及其含义。 方法。 我们展示了一条覆盖从伽马射线事件开始到几个月后仅检测到宿主星系的时间范围内的多波段光学光变曲线。结合X射线、毫米波和射电观测，我们整理了迄今为止已知最完整的XRR暴后随波段覆盖数据。 结果。 光学和X射线光变曲线的特点是早期平坦化，并在爆发开始后大约6天出现一个强烈的峰值。我们通过一个侧视喷流来解释前者，这与一些模型对XRR的预测一致；后者则用初始冲击强度相当的能量注入来解释。光谱流量分布的分析揭示了一种与周围低化学富集环境相容的消光现象。结合宿主星系中恒星形成活动的探测，我们可以加强XRR与经典长持续时间暴之间的联系。 显示英文摘要

摘要： Aims. Understand the shape and implications of the multiband light curve of GRB 050408, an X-ray rich (XRR) burst. Methods. We present a multiband optical light curve, covering the time from the onset of the gamma-ray event to several months after, when we only detect the host galaxy. Together with X-ray, millimetre and radio observations we compile what, to our knowledge, is the most complete multiband coverage of an XRR burst afterglow to date. Results. The optical and X-ray light curve is characterised by an early flattening and an intense bump peaking around 6 days after the burst onset. We explain the former by an off-axis viewed jet, in agreement with the predictions made for XRR by some models, and the latter with an energy injection equivalent in intensity to the initial shock. The analysis of the spectral flux distribution reveals an extinction compatible with a low chemical enrichment surrounding the burst. Together with the detection of an underlying starburst host galaxy we can strengthen the link between XRR and classical long-duration bursts.