Radio Spectra of Selected Compact Sources in the Nucleus of M 82

We have determined detailed radio spectra for 26 compact sources in the starburst nucleus of M82, between λλ 74 and 1.3 cm. Seventeen show low-frequency turnovers. One other has a thermal emission spectrum, and we identify it as an H II 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 φ −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 .