Neupert effect

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 electrons accelerated in the corona, which produce the hard X-rays via non-thermal bremsstrahlung), release most of their energy via collisions in the lower solar atmosphere (the chromosphere. This energy then leads to thermal (soft X-ray) emission as the chromospheric plasma heats and (somewhat counterintuitively) expands into the corona.[1] More generally, the phenomenon naturally results from juxtaposing the shorter time scales of the lower solar atmosphere with the longer time scales of cooling for the coronal flare effects. The effect is very common, but does not represent an exact relationship and is not observed in all solar flares.[3]

See also

References

  1. ^ 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.
  2. ^ 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.
  3. ^ McTiernan, Jim. "The Neupert Effect as a Function of Temperature". Retrieved 8 February 2015.


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