Multifrequency Observations of a Remarkable Solar Radio Burst

Observations of an impulsive solar radio burst from three observatories are presented. The striking observational aspects or this flare are that the time profile was identical throughout at 8.6, 15, and 86 GHz, that the spectrum was apparently flat from 15 to 86 GHz, and that there was a sharp cutoff in the spectrum between 5.0 and 8.6 GHz. The simplest interpretation of the cutoff, namely as a plasma frequency effect, leads to the conclusion that there was exceptionally high-density material in the solar corona (∼5 × 10 11 cm -3 )