New giant radio flare from Cygnus X-3

ATel #15142; S. A. Trushkin, N. A. Nizhelskij, P. G. Tsybulev (SAO RAS)
on 25 Dec 2021; 08:30 UT
Credential Certification: Sergei Trushkin (satr@sao.ru)

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During the long-term multi-frequency monitoring of the Galactic microquasars with the RATAN-600 radio telescope we have detected the giant flare at 1.2-30 GHz from the microquasar Cygnus X-3 on 31 August 2021 (ATel #14281). This flare was probably characterized a single ejection event and was over relatively soon after two weeks. But the active X-ray state continued according the Swift/BAT data at 15-50 keV, and on 18 October 2021 (MJD 59505) we have detected the very unusually long giant flare with the maximum flux about 16 Jy at 4.8 GHz (see also ATel #14989, #14509, #14518). This flare consisted of some consistent ejection events and was over after 45 days, on MJD 59550. Both the August and October flares accompanied by the Gamma-ray activity, detected by the Fermi observatory (0.1-300 GeV) and continued to MJD 59531. On 24 December 2021 (MJD 59572.48) we have detected the new giant flare with fluxes: 2.0, 7.7, 16.1, 19.1, 18.8 and 12.7 Jy at 2.3, 4.7, 8.2, 11.2, 22.3 and 30 GHz respectively (errors are within 3-4%). According to the synchrotron emission theory such spectrum is determined by optically thick and optically thin modes of the forming jets. We consider that Cygnus X-3 is in the starting of jet motion and the flare will evolve. The radio spectra during last two days are given here . The Swift/BAT data (http://swift.gsfc.nasa.gov/results/transients/CygX-3) showed the 4-fold increase of hard X-ray flux at 15-50 keV on MJD 59572. Again we can see clear association of flaring events in the radio and X-ray bands, reflecting the disk-jet coupling in the X-ray binary stars as a result of a jet production in the polar regions of accretion disk around a black hole. This giant radio flare formed just after a transition from a hyper-soft X-ray state to a soft state in Cyg X-3. Following up the VLBI mapping, mm-band, X-ray and Gamma-ray observations of Cyg X-3 could be very useful.

The Swift, Fermi and RATAN-600 light curves of the Cyg X-3 in October-December 2021