Results of studying the radio and optical variability properties of MRK 501 active galaxy

MRK 501 is a giant radio galaxy with an active core in the constellation Hercules. It is a powerful gamma source. MRK 501 has gamma cyclic variability as well as high X-ray and optical activity. MRK 501 is a quite powerful variable radio source, with a flux density at 15 GHz about 1.2 Jy. Of particular interest is the presence of cyclic brightness variations in gamma and optical ranges, which, according to modern models, may be caused by the presence of a supermassive double black hole in the core of the galaxy MRK 501. In this work, optical observatories of three countries, Ukraine (Mayaki, Heavenly Owl), Slovakia (Vihorlat) and Latvia (Baldone), took part in a joint project to study the rapid variability of AGN in radio and optical bands. The analysis of observations obtained from different observatories in V , R, I bands showed the presence of a wave-like, presumably cyclic, variability in the light curves with an average quasi-period of 46.7 days. Taking into account that a quasi-period of about 23 days was detected in the gamma range, it is most likely that we have found a harmonic (doubled value) of this period in the optical range, which is a new result. In addition, an analysis of long-term variability of MRK 501, from historical light curves of the AAVSO catalog, showed the presence of two longer cycles of variability with quasiperiods of about 1 year and about 5–6 years. It is shown that these quasi-periods, as well as their amplitudes, are unevenly distributed over an observation time interval from 2003 to 2021 (18 years) and change significantly over time.