Radio flares of Cygnus X-3

We present results from a long monitoring campaign carried out with Medicina at 8.5, 18.6, and 24.1GHz, parallel to the Metsahovi radio telescope at 37GHz, from 2017 April 4 to 11. We observe a spectral steepening from {alpha}=0.2 to 0.5 (with S_{nu}_{prop}{nu}^-{alpha}^) within 6hr of the epoch of the flare's peak maximum, and rapid changes in the spectral slope in the following days during brief enhanced emission episodes while the general trend of the radio flux density indicated the decay of the giant flare.

We further study the radio orbital modulation of CygX-3 emission associated with the 2017 giant flare and with six mini-flares observed in 1983, 1985, 1994, 1995, 2002, and 2016. The enhanced emission episodes observed during the decline of the giant flare at 8.5GHz coincide with the orbital phase {phi}~0.5 (orbital inferior conjunction). On the other hand, the light curves of the mini-flares observed at 15-22GHz peak at {phi}~0, except for the 2016 light curve, which is shifted 0.5w.r.t. the other ones.