Cygnus X-3 entered in the quenched radio and hard X-ray state

ATel #12510; S. A. Trushkin, N. A. Nizhelskij, P. G. Tsybulev, A. V. Shevchenko (SAO RAS, Russia)
on 17 Feb 2019; 13:04 UT
Credential Certification: Sergei Trushkin (satr@sao.ru)

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We continue the RATAN-600 radio telescope daily monitoring of Cyg X-3 since the giant flares in 2016-2018. During last some days we have observed that the radio fluxes from microquasar Cygnus X-3 do gradually decrease from the quiescent level 100-300 mJy to almost the quenched level 10-50 mJy at 4.6, 8.2 and 11.2 GHz on 17 February 2019 (MJD 58531.332). The dramatic quenching of the hard X-ray fluxes were detected with the Swift/BAT Hard X-ray Transient Monitor at 15-50 keV (see http://swift.gsfc.nasa.gov/results/transients/CygX-3/ and Krimm et al., 2013) also. Similar radio behaviour was detected yet by Waltman et al. (1996), as an indicator of a soon coming giant radio flare. Many times (MacCollough et al. 1997, Koljonen et al., 2010, 2018, ATel #9416, Trushkin et al., 2017) it was showed that Cyg X-3 run through a so-called "hypersoft X-rays state" before the powerful ejections or radio jets. Thus again we are right to expect a new giant flare during next 10-30 days. The last such events were detected in August 2018 (MJD 58337-350) although these giant flares were not record (comparing with the flare in September 2016, see ATel #9501), less 3.5 Jy at 8-11 GHz. We plotted the RATAN radio data and Swift hard X-ray data during last 60 days together (see http://www.sao.ru/hq/lran/XB/CygX-3/CygX-3_lc_rat_sw_2019f.png ). The spectrum on 17 Feb 2019 was extremely inverted with the spectral index of power-law fitting of +1.57 that could be related with a compact optically thick radio jets. We continue the RATAN daily observations and any radio, X-rays, of Gamma-rays observations will be very useful.

The quenched radio spectrum of Cyg X-3 on 17 February 2019