Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006spd....37.2803x&link_type=abstract
American Astronomical Society, SPD meeting #37, #28.03; Bulletin of the American Astronomical Society, Vol. 38, p.254
Astronomy and Astrophysics
Astronomy
Scientific paper
In this study, we present the results of a new approach to evaluatingthe empirical form of the energy loss rate of bremsstrahlung-producingelectrons in solar flares. The method involves a study of the sizeof extended solar flare structures as a function of photon energy.Ten M-class limb events were selected and their correspondingReuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)hard X-ray images in different energy bands were analyzed.Using a method that involves forward-fitting the source visiilities,we determined the fit parameters for each energy band. In a simplecollisional thick target model with electron injection from a point sourceinto a uniform density target, the centroid s of the emission in one leg ofthe extended source should scale as the square of the photon energyobserved, whereas for thermal bremsstrahlung models, the size shoud scaleinversely with energy e, roughly varying as e^-1/2.Our results show that observed best-fit power-law indices are clustered ina relatively narrow range centered on s e^0.5,which is at variance with the predictions of both these simple models.A non-uniform density distribution along the flare loop can be used toreconcile the data with a non-thermal collision model; however, the resultingdensity profiles are somewhat unreasonable. Therefore, our results suggest eitheran extended accelweration region and/or a substantial role for noncollisionalprocesses in the evolution of the accelerated electrons.
Emslie Gordon A.
Hurford Gordon J.
Xu Yan
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