Radio, infrared and X-ray activity of Cygnus X-3.

We present the 1-6 keV X-ray and the S-band radio light curves around 29 June 1991, when the infrared spectrum showed strong He emission lines. The X-ray and the radio data indicate that Cygnus X-3 on 29 June 1991 was in its X-ray high state, and the X-ray spectrum was soft. We also found that on 29 June 1991 Cygnus X-3 was in the decay phase of a 4 Jy radio flare, which peaked on 23 June 1991 (MJD 48430.9). In addition, 29 June 1991 was 26 days prior to the onset of the major 18 Jy flare, which peaked on 26 July 1991 (MJD 48463.9). The strong infrared emission lines and the continuum in the X-ray high intensity state are not in agreement with the prediction by van Kerkwijk (1993). However, introducing a possible relationship between the X-ray intensity and the stellar wind density could explain the observations with the van Kerkwijk model.