Radio spectra of selected compact sources in the nucleus of M82

We have determined detailed radio spectra for 26 compact sources in the starburst 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 interstellar thermal gas in M82. New information on the active galactic nucleus candidate 44.01+595 shows it to have a nonthermal falling power-law 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) mG; 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).