Thick-target processes and white-light flares

✍ Scribed by H. S. Hudson

• Book ID: 104645183
• Publisher: Springer
• Year: 1972
• Tongue: English
• Weight: 820 KB
• Volume: 24
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00153384

✦ Synopsis

Observations indicate that fast electrons in solar flares, which cause the hard X-ray burst and the impulsive microwave burst, lose energy predominantly by collisional processes. This requires a thick-target theory of the emission, for which the electron spectrum inferred from the X-ray spectrum becomes 1.5 powers steeper than in the usual thin-target theory.

The low-energy end of this spectrum contains enough energy above about 5 keV to supply the white-light continuum emission occasionally observed in major flares. The penetration of the nontherreal electrons creates long-lived excess ionization which enhances the free-free and free-bound continuum in the heated medium. The emission will occur high above the photosphere at small optical depth in the visible continuum. Thus its spectrum will extend into the infrared and ultraviolet.