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EVIDENCE THAT SYNCHROTRON EMISSION FROM NONTHERMAL ELECTRONS PRODUCES THE INCREASING SUBMILLIMETER SPECTRAL COMPONENT IN SOLAR FLARES  

Adriana V. R. Silva   Submitted: 2007-06-04 10:08

We investigate the origin of the increasing spectra observed at submm wavelengths detected in the flare on November 2nd, 2003, starting at 17:17 UT. This flare, classified as a X8.3 and 2B event, was simultaneously detected by RHESSI and the Solar Submillimeter Telescope (SST) at 212 and 405 GHz. Comparison of the time profiles at various wavelengths shows that the submm emission resembles that of the high energy X-rays observed by RHESSI while the microwaves observed by OVSA resemble that of ~50 keV X-rays. Moreover, the centroid position of the submm radiation is seen to originate within the same flaring loops of the ultraviolet and X-rays sources. Nevertheless, the submm spectra are distinct from the usual microwave spectra, appearing to be a distinct spectral component with peak frequency in the THz range. Three possibilities to explain this increasing radio spectra are discussed: (1) gyrosynchrotron radiation from accelerated electrons, (2) bremsstrahlung from thermal electrons, and finally (3) gyrosynchrotron emission from the positrons produced by pion or radioactive decay after nuclear interactions. The latter possibility is ruled out on the grounds that to explain the submm observations requires 3000 - 2 imes 105 more positrons than what is inferred from X and gamma-ray observations. It is possible to model the emission as thermal, however such sources would produce too much flux in the ultraviolet and soft X-rays. On the other hand, we are able to explain both spectral components at microwaves and submm wavelengths by gyrosynchrotron emission from the same population of accelerated electrons that emit hard X-rays and gamma rays. We find that the same 5 imes 1035 electrons inferred from RHESSI observations are responsible for the compact submm source (0.5 arcsec in radius) in a region of 4500 G low in the atmosphere, and for the traditional microwave spectral component by a more extended source (50 arcsec) in a 480 GHz magnetic field located higher up in the loops. The extreme values in magnetic field and source size required to account for the submm emission can be relaxed if anisotropy and transport of the electrons are taken into account.

Authors: Adriana V. R. Silva, G. H. Share, R. J. Murphy, J. E. R. Costa, C. G. Giménez de Castro, J.-P. Raulin, P. Kaufmann
Projects: RHESSI

Publication Status: submitted to Solar Physics
Last Modified: 2007-06-04 14:37
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EVIDENCE THAT SYNCHROTRON EMISSION FROM NONTHERMAL ELECTRONS PRODUCES THE INCREASING SUBMILLIMETER SPECTRAL COMPONENT IN SOLAR FLARES

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
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