Radio emission from GRO J1655-40 during the 1994 jet ejection episodes

We report multifrequency radio observations of GRO J1655-40 obtained with t he Australia Telescope Compact Array, the Molonglo Observatory Synthesis Te lescope and the Hartebeesthoek Radio Astronomy Observatory at the time of t he major hard X-ray and radio outbursts in 1994 August-September. The radio emission reached levels of the order of a few Jy and was found to be linea rly polarized by up to 10%, indicating a synchrotron origin. The light curv es are in good agreement with those measured with the VLA, but our closer t ime sampling has revealed two new short-lived events and significant deviat ions from a simple exponential decay. The polarization data show that the m agnetic held is well ordered and aligned at right angles to the radio jets for most of the monitoring period. The time evolution of the polarization c annot be explained solely in terms of a simple synchrotron bubble model, an d we invoke a hybrid "core-lobe" model with a core which contributes both s ynchrotron and free-free emission and "lobes," which are classical synchrot ron emitters.