Beginning of the new giant flare from Cygnus X-3
ATel #13461; S. ATrushkin, P. G. Tsybulev, N. N. Bursov, N. A. Nizhelskij, A. V. Shevchenko (SAO RAS, Russia)
on 8 Feb 2020; 18:42 UT
Credential Certification: Sergei Trushkin (satr@sao.ru)
Subjects: Radio, Millimeter, Infra-Red, X-ray, Gamma Ray, Binary
In the intensive multi-frequency monitoring of the Galactic microquasars with RATAN-600 radio telescope we have received daily light curves of their radio emission at 1.3-30 GHz. On 16 January (MJD 58864) we have detected fluxes lower 5 mJy at 4.7 GHz from Cyg X-3 and then during next 12 days radio emission was very low. In the same dates the hard X-ray emission (Swift/BAT at 12-50 keV, here HXR) was almost zero (< 0.006 count/cm^2/s). Usually such a state, named hyper-soft state, suggested that in Cygnus X-3 a giant radio flare will occur during close weeks after transition to a simple soft, and then to a hard state.
First short and small event happened after 12 days (MJD 58876), when fluxes grew to ~100 mJy at 4.7 GHz. Second the brighter event was detected after MJD 58881.3 with peaked fluxes near 1 Jy and optically thick spectrum. At last we have detected the third event - a giant flare - on MJD 58885.3. Today the fluxes increased to 10 Jy at 4.7 GHz on MJD 58887.35 already with the optically thin spectrum at frequencies higher 4.7 GHz, having the spectral index -0.28. The spectra during last days are given here .
The measurements after 2.5 hours showed further increase of the fluxes at 4.7 and 8.6 GHz up to 13 Jy. Probably this flare is evolving yet. We must notice that HXR flux increased to 0.033 count/cm^2/s after MJD 58885.5. That means that the binary entered in a soft state.
The flaring radio activity of Cygnus X-3 goes on, probably it is related with the gamma-ray flaring activity from Cygnus X-3 detected by AGILE by Piano et al. in ATel #13458.
The further observations of Cygnus X-3 would be extremely useful.
The RATAN multi-frequency light curves of Cygnus X-3 in January-February 2020