Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...437..522g&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 437, no. 1, p. 522-528
Astronomy and Astrophysics
Astronomy
26
Brightness Distribution, Gamma Ray Astronomy, Microwaves, Radio Astronomy, Solar Magnetic Field, Solar X-Rays, Sunspots, X Ray Astronomy, Japanese Spacecraft, Radio Emission, Spaceborne Astronomy, Very Large Array (Vla), X Ray Telescopes
Scientific paper
We report observations of transient microwave (2 cm) brightenings and their relationship with brightenings in soft X-rays. The peak flux of the microwave brightenings observed by the Very Large Array (VLA) is smaller than the previously reported fluxes by two orders of magnitude. The microwave sources were highly polarized (up to 100%) and were situated on the periphery of a sunspot umbra. Among the many transients observed in X-rays by Yohkoh, two were observed simultaneously in microwaves. The microwave sources were found to be closer to the umbra of the sunspot than were the X-ray loops. It seems that the microwave sources are located at the footpoints of the looplike X-ray transients. Using the combined VLA, Yohkoh, and Mees data set, we determine the physical parameters of the loop in which the brightenings occur. We find that an increase in emission measure accompanied by small-scale heating can account for the X-ray brightening. The microwave emission can be interpreted as thermal gyroresonance or nonthermal gyrosynchrotron processes during the X-ray brightening. The magnetic field in the microwave-source region is found to be 1200-1800 G. The observations also provide evidence for temperature gradient in the coronal loops.
Canfield Richard C.
de La Beaujardiere J.
Gopalswamy Nat
Kundu Mukul R.
Lemen James R.
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