高红移耀变体4C 38.41光学多波段光变性质

4C 38.41是一颗红移为1.813、可分类为平谱射电类星体的耀变体,使用一台85 cm望远镜在2018年2月22日至26日期间对其进行了光学V和R波段测光观测,得到两个波段的准同时数据.基于这些数据分析了该源在不同光变时标下的光变特性.结果表明:这颗源在观测期间处于较弱的活动状态, V和R波段星等(V, R)总变化均约为0.20等.在天内时标下,其中3晚探测到了该源的天内光变,另有一晚可能存在天内光变.此外,通过色指数和时延分析发现4C 38.41在不同时标下都展现越亮越红行为,与大多数平谱射电类星体类似,但在最后一晚4C 38.41在颜色-星等图上呈现出v字形,即首先展现越亮越红行为,然后转变为越亮越蓝行为,这可能是由该源的辐射在吸积盘主导和喷流主导之间的转换造成的.此外在第2晚探测到了V、R波段之间的时延,这是首次在高红移耀变体中探测到不同光学波段光变之间的时延,可以用随机同步辐射小结构模型来解释.

Multi-Wavelength Optical Variability of High Redshift Blazar 4C 38.41

4C 38.41 is a blazar with a redshift of 1.813 and is classified as a flat spectrum radio quasar. The photometric observations on this object were carried out quasi-simultaneously in the optical V and R bands by using a 85cm telescope from February 22, 2018 to February 26, 2018. The variability properties of the source on diverse timescales are analyzed. The results show that this source is in a weak active state during the whole observation period, and the variation amplitudes in the V and R bands are both about 0.2 mag. Intra-day variability is detected in three nights and probably in one more night. In addition, the colour-magnitude relationship and inter-band cross-correlation analysis are performed. The results show that 4C 38.41 exhibited a redder-when-brighter behaviour on both intra- and inter-day timescales, which is consistent with those of most flat-spectrum radio quasars. In the last night, 4C 38.41 exhibited a v-shape in the colour-magnitude diagram, i.e., it showed redder-when-brighter behaviour at first and then become bluer-when-brighter trend. This phenomenon can be interpreted by the change of the dominance between the accretion disk emission and the jet emission in this source. In addition, a time delay between the V- and R-variations is detected on the second night. This is the first reported time delay between the variations in different optical bands in a high redshift blazar, which can be interpreted by the model of random small synchrotron cells.