Other
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.9326k&link_type=abstract
American Astronomical Society Meeting 210, #93.26; Bulletin of the American Astronomical Society, Vol. 39, p.215
Other
Scientific paper
Sunquakes, the helioseismic response to solar flares, are caused by strong localized hydrodynamic impacts in the photosphere, which are observed directly in SOHO/MDI Dopplergrams during the impulsive phase. These impacts correlate very well both temporary and spatially with hard X-ray sources, and in some cases are close to gamma-ray sources imaged by RHESSI. A common paradigm is
the sunquake events are caused by accelerated protons because protons carry more momentum and penetrate much deeper into the solar atmosphere than electrons which loose most of their energy in the upper chromosphere. I present the results of analysis of the hydrodynamic
response for the sunquake events when both hard X-rays and gamma-rays were observed by RHESSI. In one event, X5.6 flare of July 23, 2002, the hard X-ray and gamma-ray sources were significantly separated from each other, approximately by 20" (with 5-sigma confidence). Analysis of MDI Dopplergrams reveals hydrodynamic and seismic responses associated the hard X-ray source and shows no significant signal in the gamma-source area. These observations effectively rule out high-energy protons as a source of sunquakes. Furthermore, detailed analysis of the dynamics of sunquake sources reveals their close association with expanding flare ribbons, and thus with the magnetic reconnection process. The fast motion of these sources results in strong anisotropy of the seismic waves, clearly observed in the MDI data. The general picture that comes from the analysis of MDI and RHESSI is consistent with the previously developed hydrodynamic thick-target model, in which electrons heat the upper chromosphere to high temperatures generating a high-pressure region, expansion of which causes a high compression shock, which reaches the photosphere and excites the seismic waves. I discuss how the observations and modeling of sunquakes and their sources help to understand processes of the energy release and transport in solar flares.
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