The going-on bright flare from the X-ray binary Cygnus X-3
ATel #16581; S. A. Trushkin, N. N. Bursov, A. V Shevchenko, N. A. Nizhelskij, P. G. Tsybulev (SAO RAS, Russia)
on 9 Apr 2024; 16:50 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Sergei Trushkin (satr@sao.ru)
Subjects: Radio, Millimeter, X-ray, Gamma Ray, >GeV, Binary, Black Hole
We carry out the long-term multi-frequency monitoring of the Galactic microquasars with the RATAN-600 radio telescope almost daily in 2024 at 1.24-30 GHz. We have detected the activity from
the microquasar Cygnus X-3 on 27 March after the long period of the very low hard X-ray state at 15-50 keV, named by a hyper-soft state, as according to the Swift/BAT public domain data.
After 31 March (MJD 60399.218) we have detected the start of a giant flare from the object, which reached maximal flux densities about 14 Jy at 2.3 GHz on 3 April (MJD 60403.21). Before on 16-17 February we have already detected the similar giant flare with maximal fluxes about 15 Jy at 2.3 GHz (see Farah el al., ATel #16466 and Egron et al. ATel #16577), while the hyper-state continued in total March. Again as usually for giant flares March-April flare is probably characterized a single ejection event while up to now it is not over. The beginning of the flare followed to the linear law from time as the multi-azimuthal measurements have showed (see Trushkin et al. 2023).
The evolution of the flare evolved from optically thick to optically thin mode at frequencies lower
2.3 GHz. At frequencies 4.7-11.2 GHz) the spectral index of radio emission changed from positive
values to -0.5, and further to -0.75. See selected daily spectra during the flare
here .
It worth to note that 31 March (MJD 60400.5) the Fermi/LAT telescope detected the
most bright flux (3.79e10-6 photons/cm^2/s) for total period of the observations of Cyg X-3.
The light curves at 2.3-30 GHz during the March-April flare from Cyg X-3
