It has been suggested that the peculiar properties of the luminous Type Ic supernova SN 1998bw and its low-energy gamma-ray burst GRB 980425 may be understood if they originated in a standard gamma-ray burst explosion viewed far from the axis of the relativistic jet .
In this scenario , strong radio emission is predicted from the jet on a timescale 1 to 10 years after the explosion as it decelerates and spreads into our line of sight .
To test this hypothesis we have carried out late-time radio observations of SN 1998bw at t = 5.6 years , yielding upper limits which are consistent with the continued fading of the supernova .
We find these limits to be consistent with an off-axis jet only if the progenitor mass loss rate is \dot { M } \lesssim 4 \times 10 ^ { -7 } M _ { \odot } yr ^ { -1 } ( for a wind velocity v _ { w } = 1000 
km s ^ { -1 } ) or the fraction of the shock energy in magnetic fields is \epsilon _ { B } \lesssim 10 ^ { -3 } .
These values are low relative to those inferred for cosmological GRBs .
We combine the SN 1998bw measurements with existing observations for a sample of 15 local Type Ibc supernovae to estimate that at most 6 % produce collimated , relativistic outflows .