The Neupert effect refers to an empirical tendency for high-energy ('hard') X-ray emission to coincide temporally with the rate of rise of lower-energy ('soft') X-ray emission of a solar flare.[1] Here 'hard' and 'soft' mean above and below an energy of about 10 keV to solar physicists, though in non-solar X-ray astronomy one typically sets this boundary at a lower energy.
This effect gets its name from NASA solar physicist and spectroscopist Werner Neupert, who first documented a related correlation (the integral form) between microwave (gyrosynchrotron) and soft X-ray emissions in 1968.[2] The standard interpretation is that the accumulated energy injection associated with the acceleration of non-thermal electrons (which produce the hard X-rays via non-thermal bremsstrahlung) release energy in the lower solar atmosphere (the chromosphere); this energy then leads to thermal (soft X-ray) emission as the chromospheric plasma heats and expands into the corona.[1] The effect is very common, but does not represent an exact relationship and is not observed in all solar flares.[3]
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References edit
- ^ a b Veronig, Astrid; Brown, John; Dennis, Brian; Schwartz, Richard; Sui, Linhui; Tolbert, Kimberley (March 2005). "Physics of the Neupert Effect: Estimates of the Effects of Source Energy, Mass Transport, and Geometry Using RHESSI and GOES Data". The Astrophysical Journal. 621 (1): 482–497. Bibcode:2005ApJ...621..482V. doi:10.1086/427274.
- ^ Neupert, Werner (July 1968). "Comparison of Solar X-Ray Line Emission with Microwave Emission during Flares". Astrophysical Journal. 153: L59. Bibcode:1968ApJ...153L..59N. doi:10.1086/180220.
- ^ McTiernan, Jim. "The Neupert Effect as a Function of Temperature". Retrieved 8 February 2015.
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