We have determined detailed radio spectra for 26 compact sources in the starburst nucleus of M82 , between \lambda \lambda 74 and 1.3 cm .
Seventeen show low-frequency turnovers .
One other has a thermal emission spectrum , and we identify it as an \ion H2 region .
The low frequency turnovers are due to absorption by interstellar thermal gas in M82 .

New information on the AGN candidate , 44.01+595 , shows it to have a non-thermal falling powerlaw spectrum at the highest frequencies , and that it is strongly absorbed below 2 GHz .

We derive large magnetic fields in the supernova remnants , of order 1-2 ( 1 + k ) ^ { 2 / 7 } \phi ^ { -2 / 7 } milliGauss , hence large pressures in the sources suggest that the brightest ones are either expanding or are strongly confined by a dense interstellar medium .
From the largest source in our sample , we derive a supernova rate of 0.016 yr ^ { -1 } .