Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Conditions for electron-cyclotron maser emission in the solar corona   Context. The Sun is an active source of radio emission ranging from long
duration radio bursts associated with solar flares and coronal mass ejections
to more complex, short duration radio bursts such as solar S bursts, radio
spikes and fibre bursts. While plasma emission is thought to be the dominant
emission mechanism for most radio bursts, the electron-cyclotron maser (ECM)
mechanism may be responsible for more complex, short-duration bursts as well as
fine structures associated with long-duration bursts. Aims. We investigate the
conditions for ECM in the solar corona by considering the ratio of the electron
plasma frequency {\omega}p to the electron-cyclotron frequency {\Omega}e. The
ECM is theoretically possible when {\omega}p/{\Omega}e < 1. Methods.
Two-dimensional electron density, magnetic field, plasma frequency, and
electron cyclotron frequency maps of the off- limb corona were created using
observations from SDO/AIA and SOHO/LASCO, together with potential field
extrapolations of the magnetic field. These maps were then used to calculate
{\omega}p/{\Omega}e and Alfven velocity maps of the off-limb corona. Results.
We found that the condition for ECM emission ({\omega}p/{\Omega}e < 1) is
possible at heights < 1.07 R_sun in an active region near the limb; that is,
where magnetic field strengths are > 40 G and electron densities are greater
than 3x10^8 cm-3. In addition, we found comparatively high Alfv\'en velocities
(> 0.02 c or > 6000 km s-1) at heights < 1.07 R_sun within the active region.
Conclusions. This demonstrates that the condition for ECM emission is satisfied
within areas of the corona containing large magnetic fields, such as the core
of a large active region. Therefore, ECM could be a possible emission mechanism
for high-frequency radio and microwave bursts.

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The categories of this paper are: hep-th
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The categories of this paper are: math
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The categories of this paper are: econ
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The categories of this paper are: hep-ex
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The categories of this paper are: plasm-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: q-alg
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: physics
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The categories of this paper are: chem-ph
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The categories of this paper are: cond-mat