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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.63] Multi-wavelength Observations of Transient Microwave Brightenings in a Solar Active Region

J. Zhang, N. Gopalswamy, M. R. Kundu, E. J. Schmahl (Dept. of Astronomy, Univ. of Maryland, College Park, MD 20742), J. R. Lemen (Lockheed Martin Advanced Tecknology Center, Building 252, Dept. 91-30, 3251 Hanover ST. Palo Alto, CA 94304)

We present multi-wavelength Very Large Array observations of two transient microwave brightenings (TMBs) in the solar active region 7135. The events were observed at 2 cm (spatial resolution \sim2'') and 3.6 cm (spatial resolution \sim3'') with a temporal resolution of 3.3 s in a time-sharing mode. Soft X-ray data (about 5'' spatial resolution) were available from the Soft X-ray Telescope on board the YOHKOH satellite. The 2 cm and 3.6 cm emission sources were very compact, located near the footpoint of the magnetic loops seen in the X-ray images. The TMBs traced out the three dimensional structure of the magnetic loops where the transient brightenings occurred. For the two events reported in this paper, the projected angular separation between the centroids of 2 and 3.6 cm source is about 2.3'' and 3.1'', respectively. We interpret the spatial and temporal distributions as implying that the 2 and 3.6 cm flux is mainly due to thermal gyro-resonance emmision. The 2 cm emission seems to be at the 3rd gyro-harmonic coming from the 1800 G gyro-resonance layer. The 3.6 cm emission seems to be at both the 2nd and 3rd harmonics, originating from gyro-resonance layers with a magnetic field of 1500 G and 1000 G, respectively. However, the two gyro-resonance layers for 3.6 cm emission are not resolved with the current spatial resolution. The estimated magnetic field gradient near the footpoint of the magnetic loop is about 0.17 G km^-1 and 0.22 G km^-1 for the two events.

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