RADIO OBSERVATIONS OF GRS-1124-68 (X-RAY NOVA MUSCAE 1991)

We present radio observations of the bright soft X-ray transient source GRS 1124-68 (Nova Muscae 1991), which was discovered in X-rays on 1991 January 8, and first detected optically on January 13, Radio observations of GRS 1124-68 began on January 17, We report here on observations made with the Molonglo Observatory Synthesis Telescope and with the Australia Telescope Compact Array. When first observed in the radio the flux density was similar to 150 mJy at 4.7 GHz and already decreasing, The radio observations of the next few days have much in common with. observations of earlier strong X-ray transients. However, a second burst of radio emission from GRS 1124-68 was observed with both telescopes, beginning on about January 28. We believe that the observations of this later radio burst are the first observations of the rising phase of a radio transient associated with a soft X-ray transient source. Furthermore, the observations of this rising phase of emission cannot be fitted using the standard model for such radio transients.