Prolonged millimeter-wave radio emission from a solar flare near the limb
Abstract
We present a multi-wavelength analysis of a gradual radio flare on June 27, 1993 which showed emission at millimeter waves long after the soft X-ray flux had peaked. The radio flare located at S12 E75 was associated with a GOES class M3.6 flare that lasted for more than one hour and hard X-ray emission during the rising phase of the soft X-ray/radio emission. The maximum radio flux density at 35 GHz was 60 sfu, but the calculated thermal bremsstrahlung flux from the GOES soft X-rays was less than half of that. The possible explanations for this prolonged millimeter wave emission could be accelerated high-energy electrons gyrating along the field-lines (nonthermal gyrosynchrotron emission) or thermal bremsstrahlung from evaporating chromospheric warm and dense plasma (cool enough to go undetected by GOES), or a mixture of these. Our model calculations show that even an inhomogeneous source containing both kinds of particles would not be able to produce such a spectral shape. A second source with extremely high electron densities (>1016 m-3), large source dimensions (>1015 m2), and very low temperatures (<106 K) must be assumed to explain the observed radio spectra.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2002
- DOI:
- 10.1051/0004-6361:20021431
- Bibcode:
- 2002A&A...396..683P
- Keywords:
-
- Sun: chromosphere;
- Sun: corona;
- Sun: flares;
- Sun: radio radiation;
- X-rays: general