On the Origin of Intense Radio Emission from the Brown Dwarfs

Resumo

Observations of quasi-periodic intense radio emission at 2–8 GHz from the brown dwarfs with a brightness temperature of up to T_b ∼ 10¹³ K and with a fairly narrow radiation pattern initiated a series of studies in which the radiation was interpreted in terms of the electron cyclotron maser emission generated by energetic electrons with the “loss cone.” The plasma mechanism of the radio emission was excluded from consideration because it requires that the electron plasma frequency should exceed the electron gyrofrequency in the source of the radio emission, i. e., ν_p > ν_c. In this paper, we propose a coherent plasma radiation mechanism for intense radio emission from the brown dwarfs. The possibility of the formation of hot extended coronae in the magnetic loops that occur in the atmospheres of the brown dwarfs as a result of the photospheric convection is shown. The electric currents generated in the magnetic loops by photospheric convection lead to the plasma heating and elevation of the “squeezed” atmosphere. This ensures that the condition ν_p > ν_ce required for the plasma mechanism of radio emission is fulfilled at the coronal levels. In addition, the pumping mechanism supplying energetic particles into the coronae of the brown dwarfs, which maintain the long-term generation of intense radio emission from these stars, is studied. The parameters of the Langmuir turbulence explaining the observed properties of the radio emission from the brown stars are determined.