The Intraday multi-frequency radio observations of the microquasar Cygnus X-3

The results of the intraday multi-frequency monitoring of Cygnus X-3 during four flares in 2019-2021 are presented. Study of the radio spectra evolution at different time scales is the key for understanding the formation of jets during the accretion of the matter from a Wolf-Rayet star to a black hole or a neutron star. We carried out long-term almost daily observations of bright microquasars at frequencies 1.2-30 GHz during last years (see Trushkin et al in this value). Since August 2016, Cygnus X-3 has entered a new active phase (as a rule, characterized by the hyper-soft X-ray state). We detected the giant flares in 2016, 2017, 2019, 2020 and 2021. The first time the intraday observations of the last flares (2019-2021) were carried out with the southern sector of the antenna with a flat mirror, when 31 measurements at 1-3 frequencies around a local culmination time were made with time steps of about ten minutes. We have detected a clear evolution of the spectra during the 5.5 hours of the sets. We detected the very beginning of the flare on 18 April 2019 and found the linear growth of the fluxes, starting sumultaniously on MJD 58651.0. These new data could be used for the modeling of synchrotron radiation in relativistic jets. The Multifaceted Universe: and -