Study of the fast variability of the radio galaxy 3C 84 (Perseus A) in optical bands

The extragalactic radio source 3C 84 (also known as Perseus A) is the active nucleus of giant galaxy NGC 1275, the largest in the Perseus cluster of galaxies (Abell 426). It is one of the brightest X-ray clusters of galaxies. The nucleus of galaxy NGC 1275 (Seyfert II type) is a powerful radio source of the Northern sky (flux density at a frequency 8 GHz is about 30 Jy). However, in spite of the intensive study of 3C 84 in the X-ray and gamma ranges, there are still quite a few optical observations that allow distinguish-ing intra-night variability. This paper shows some results of studies of fast day-to-day variability of 3C 84 in BVRI filters, based on observations at observatories in Ukraine (Mayaki), Latvia (Baldone), and Slovakia (Vihorlat). The telescopes are located in close meridional directions, which makes it possible to carry out quasi-simultaneous observations. According to these data, the light curves of 3C 84 suggest the presence of quasicyclic variations with a period about 12–19 days. Analysis of intra-night variability (time interval 5 Feb – 21 Mar 2021) according to the Baldone observatory (Latvia) showed presence at 11 Feb 2021, significant manifestation of variability with characteristic times about 10 and 1 hour. Presumably, inta-night variability was recorded on 2 Mar and 18 Feb 2021, with characteristic times 7.8 hours, 54 minutes and 4.8 hours, 1.5 hours, respectively. At the same time, manifestation of inta-night variability is episodic. Most often, variations in the 3C 84 brightness within individual nights are linear or parabolic trend changes or just noise. The amplitude of intra-night variability relative to trend changes was about 0.01 mag.