Radio spectra of selected compact sources in the nucleus of M82

We have determined detailed radio spectra for 26 compact sources in the sta rburst nucleus of M82, between 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 result from absorption by int erstellar thermal gas in M82. New information on the active galactic nucleu s candidate 44.01+595 shows it to have a nonthermal falling power-law spect rum 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) mG; hence, large pressures in the sources suggest that the brightest ones are either expanding or are strongly confined by a dens e interstellar medium. From the largest source in our sample we derive a su pernova rate of 0.016 yr(-1).