On the origin of the type-III radiation observed near the Sun

AIMS 1. To use Parker Solar Probe (PSP) data to test the accepted theory that type-III radiation is produced by counter-streaming Langmuir waves that coalesce to produce the electromagnetic wave at twice the Langmuir frequency. 2. If this theory is found to be incorrect, to replace it with a description of type-III generation that is consistent with the PSP data. METHODS To obtain new properties of the Langmuir wave and its harmonics, their phase velocities and density fluctuations were measured. If the harmonic wave was electromagnetic, as in the accepted theory, these quantities would not be measurable. However, in an electrostatic wave, they would be measurable by the PSP instruments. RESULTS The Langmuir wave and its harmonics at frequencies of nωp, where ωp = 2PI*125 kHz is the Langmuir frequency and n = 2, 3, 4, 5, 6, and 7, were measured in an active type-III event. The lowest harmonics contained density fluctuations, so they were electrostatic waves and not type-III emissions. This result was bolstered by measuring their very slow phase velocities ( 2000 km/sec) which are not those of a type-III wave. Thus, the harmonic waves were not a result of the three-wave interaction (as required by the accepted theory) but they were electrostatic antenna waves produced by radiation of the Langmuir wave. As at least the first harmonic wave evolved through density irregularities, its wave number decreased and it became the electromagnetic wave that was the type-III radiation.