VLA observations of solar flares, interpreted with optical, X-ray, and other microwave data

Journal Article · Thu Mar 01 04:00:00 EST 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156885· OSTI ID:6331390

Marsh, K A; Zirin, H; Hurford, G J

Three small solar flares were observed from the active region McMath 14979 during 1655--1725 UT on 1977 October 12, using the southwest arm of the Very Large Array (VLA) at 4.9 Ghz. These observations showed the presence of two distinct flare components: (1) A dominant broad component of size approx.10'', with gradual rise-and-fall behavior and 25%--50% circular polarization, and (2) small impulsive components of size approx.2''--4'', 53%--98% circularly polarized.Simultaneous interferometric observations of the 1703 UT flare with the Owens Valley solar interferometer at 10.7 Ghz, together with the VLA data, fixed the location of the broad component in two dimensions. Comparison with H..cap alpha.. photographs and magnetograms showed that this component was located in the magnetic arch at whose footpoints the H..cap alpha.. flare occurred. The electron temperature and emission measure implied by OSO 8 soft X-ray observations yielded a corresponding free-free microwave flux which entirely accounted for the observed emission at 10.7 GHz. The microwave spectrum at lower frequencies (2.7 GHz and 4.9 GHz) was then consistent with thermal gyroresonance radiation in a magnetic field of approx.300 gauss. The radio, optical, and X-ray observations thereby suggest that the broad microwave component was a thermal cloud trapped in a magnetic arch. The impulsive events probably occurred at the positive-polarity footpoints of this arch.

• Research Organization: Big Bear Solar Observatory, Hale Observatories, California Institute of Technology
• OSTI ID: 6331390
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 228:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ELECTROMAGNETIC RADIATION
ENERGY SPECTRA
INTERFEROMETRY
IONIZING RADIATIONS
MICROWAVE RADIATION
POLARIZATION
RADIATIONS
RADIOWAVE RADIATION
SOLAR ACTIVITY
SOLAR FLARES
SOLAR RADIATION
SOLAR RADIOWAVE RADIATION
SPECTRA
X RADIATION