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Published June 10, 2012 | Accepted Version + Published
Journal Article Open

Electron-beam-induced Radio Emission from Ultracool Dwarfs


We present the numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECM) with different plasma parameters and different magnetic field strengths for a relatively small region and short timescale in an attempt to interpret the recent discovered intense radio emission from ultracool dwarfs. We find that a large amount of electromagnetic (EM) field energy can be effectively released from the beam-driven ECM, which rapidly heats the surrounding plasma. A rapidly developed high-energy tail of electrons in velocity space (resulting from the heating process of the ECM) may produce the radio continuum depending on the initial strength of the external magnetic field and the electron beam current. Both significant linear polarization and circular polarization of EM waves can be obtained from the simulations. The spectral energy distributions of the simulated radio waves show that harmonics may appear from 10 to 70ν_(pe) (ν_(pe) is the electron plasma frequency) in the non-relativistic case and from 10 to 600ν_(pe) in the relativistic case, which makes it difficult to find the fundamental cyclotron frequency in the observed radio frequencies. A wide frequency band should therefore be covered by future radio observations.

Additional Information

© 2012 American Astronomical Society. Received 2011 December 14; accepted 2012 April 4; published 2012 May 25. Research at the Armagh Observatory is grant-aided by the N. Ireland Department of Culture, Arts, and Leisure. We also thank the Leverhulme Trust for their support of this project. A.A. gratefully acknowledges the support of the Bulgarian National Science Fund (Grant No. DDVU02/40−2010). A.L.M. thanks STFC for support through a Rolling Grant. S.Y. thanks the 9th international space simulation school for the tutorial courses and Professor Y. Omura for discussions. S.Y. also thanks Dr. J. McDonald in NUI,Galway for discussions.We thank the referee for his/her helpful and constructive comments.

Attached Files

Published - Yu2012p18830Astrophys_J.pdf

Accepted Version - 1204.2261.pdf


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