Electron-cyclotron maser emission by power-law electrons in coronal loops

Details Electron-cyclotron maser emission by power-law electrons in coronal loops Electron-cyclotron maser emission by power-law electrons in coronal loops

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009a%26a...493..623t&link_type=abstract

Astronomy and Astrophysics, Volume 493, Issue 2, 2009, pp.623-628

Astronomy and Astrophysics

Astrophysics

4

Masers, Plasmas, Radiation Mechanisms: Nonthermal, Sun: Radio Radiation

Scientific paper

Context: The electron-cyclotron maser (ECM) instability is an important mechanism that amplifies electromagnetic radiation directly by nonthermal electrons trapped in magnetic fields. The nonthermal electrons frequently have a negative power-law distribution with a lower energy cutoff (E_c), which will depress the instability. Aims: In this paper, it is shown that the lower energy cutoff behavior of power-law electrons trapped in coronal loops can drive the ECM instability efficiently. Methods: Based on the dispersive relation for high-frequency waves and distribution function for power-law electrons with a lower energy cutoff in a coronal loop, the growth rates of the O and X mode waves at fundamental and harmonic frequencies are calculated. Results: The results show that the instability is driven when δ>α because of a population inversion below the cutoff energy E_c, where δ is the steepness index describing the cutoff behavior and α the power-law spectrum index. The growth rates increase with δ and E_c, but decrease with α, σ, and Ω, where σ is the magnetic mirror ratio of the loop and Ω the ratio frequency in the loop. Conclusions: This novel driving mechanism for the ECM emission can be expected to have a potential importance for understanding the microphysics of radio bursts from the Sun and others.

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