  The well-known black-hole X-ray transient A0620-00 was a bright radio source
during the first part of its outburst in 1975. We have revisited the available
data and find for the first time evidence that the source exhibited multiple
jet ejections. Rapid radio spectral changes indicate the addition of at least
three new components which are initially optically thick. From single baseline
interferometry taken about three weeks after the start of the X-ray outburst we
find that the source is extended on arcsec scales and infer a relativistic
expansion velocity. Some of the other (soft) X-ray transients, such as GS
1124-68 and GS 2000+25, show very similar X-ray outburst light curve shapes to
that of A0620-00, while their radio outburst light curve shapes are different.
We suggest that this is due to the radio emission being strongly beamed in
outburst, whereas the X-ray emission remains isotropic. Since this effect is
stronger at higher jet velocities, this strengthens our conclusion that the
jets in A0620-00 and other soft X-ray transients move with relativistic speeds.
