Monitoring of the giant flare of Cygnus X-3 with the Sardinia Radio Telescope
ATel #13475; E. Egron, A. Pellizzoni, D. Perrodin, M. Pilia, M. Bachetti, M. Pili, L. Schirru (INAF-OAC), N. Iacolina (ASI)
on 13 Feb 2020; 22:48 UT
Credential Certification: Elise Egron (elise.egron@inaf.it)
Subjects: Radio, Binary, Black Hole, Transient
The daily monitoring performed with the RATAN-600 detected a new quenched radio state (< 5 mJy 4.7 GHz) of the microquasar Cyg X-3 on 16 January 2020 (MJD 58864). The very low radio emission was associated with an hyper-soft X-ray state (< 0.006 counts/cm^2/s from Swift/BAT, 15-50 keV).
After a small rise of flux (< 1 Jy) during two events, the radio flux suddenly increased in a significantly way on MJD 58886 (7 February 2020) from 1 Jy to 10 Jy at 4.7 GHz within a day. This intense and quick increase marked the beginning of a new giant radio flare (Trushkin et al. in ATel #13461), which is also associated with a gamma-flare detected by AGILE on MJD 58884-58886 (Piano et al. in ATel #13458).
We triggered a daily monitoring program with the Sardinia Radio Telescope (SRT; 64-m dish) at 7.2 GHz and 24.7 GHz in order to follow the evolution of the giant flare. A first peak (11.0+/-0.5 Jy at 7.2 GHz and 8.7 +/-0.9 Jy at 24.7 GHz) was reached on MJD 58888 (9 February), then an even brighter second peak (15.0+/-0.7 Jy at 7.2 GHz and 8.7 +/-0.9 Jy at 24.7 GHz) two days later, on MJD 58890.
The radio flux is now slowly decreasing (10.8+/-0.5 Jy at 7.2 GHz and 5.5 +/-0.6 Jy at 24.7 GHz) while the hard X-ray flux (Swift/BAT) is increasing (0.024 counts/cm^2/s on MJD 58891: http://swift.gsfc.nasa.gov/results/transients/CygX-3/ ).
We thank E. Molinari and S. Poppi for allowing us to promptly trigger the observations.
SRT light curves of Cyg X-3 at 7.2 GHz and 24.7 GHz
