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

Abstract

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 (V, R) 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 interband 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, which can be interpreted by the model of random small synchrotron cells.