The nearest starburst, in M82, is being studied intensively with the VLA, MERLIN and VLBI. The VLA/MERLIN map at 20cm wavelength is the best overall representation of the radio source. As well as diffuse emission there are $\sim 50$ compact sources many which have been resolved into shells. The shell structures confirm that the compact sources are indeed supernova remnants (SNR) and hence M82 is a convenient laboratory for studying SNR. European VLBI observations over an 11 year time baseline have measured expansion velocities of ±9000 km/s in several remnants indicating that their ages range from about 35 to about 100 years. Assuming similar expansion velocities for the larger shells, mapped with MERLIN, implies that their ages are up to 1000 years. Future VLBI observations should enable the ages of many more remants to be estimated and hence allow the present supernova rate to be determined.
Wills, Muxlow, Pedlar (Manchester)