The 2006 radio outbursts of a microquasar Cygnus X-3: Observations and data

We present the results of multi-frequency observations of radio outbursts of the microquasar Cygnus X-3 in 2006 February and March with the Nobeyama 45-m telescope, the Nobeyama Millimeter Array, and the Yamaguchi 32-m telescope. Since the prediction of a flare by RATAN-600, the source was monitored from January 27 (UT) with these radio telescopes. At the eighteenth day after the quench of activity, successive flares exceeding 1 Jy were successfully observed. The time scale of the variability in the active phase is presumably shorter in higher frequency bands. We also present the result of a follow-up VLBI observation at 8.4 GHz with the Japanese VLBI Network 2.6 d after the first rise. A VLBI image exhibits a single core with a size of < 8 mas (80 AU). The observed image is almost stable, although the core shows a rapid variation in the flux density. No jet structure can be seen at a sensitivity of T-b (brightness temperature) = 7.5 x 10(5) K.