The Neupert effect refers to an empirical tendency for high-energy ('hard')

X-ray X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

emission to coincide temporally with the rate of rise of lower-energy ('soft') X-ray emission of a

solar flare A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other sola ...

. 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. 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 ''Bremsstrahlung'' (), from "to brake" and "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typicall ...

) release energy in the lower solar atmosphere (the

chromosphere A chromosphere ("sphere of color") is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively. In the S ...

); this energy then leads to

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

(soft X-ray) emission as the chromospheric plasma heats and expands into the corona. The effect is very common, but does not represent an exact relationship and is not observed in all solar flares.

References

X-rays {{astronomy-stub

See also

References