A search for hard X-ray microflares near solar minimum

✍ Scribed by R. P. Lin; K. C. Hurley; D. M. Smith; R. M. Pelling

• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 435 KB
• Volume: 135
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00146698

✦ Synopsis

Near solar maximum, hard X-ray microflares with peak 20 keV fluxes of > 10-2 (cm 2 s keV)-1, more than ten times smaller than for typical flares and subflares, can occur at the rate of about once every five minutes. We report here on a search for hard X-ray microflares made on a long duration balloon flight in February 1987 near solar minimum, at a time when no active regions were on the Sun. No microflares were observed over a total observing time of 16.5 hours spread over three days, implying a statistical upper limit to their rate of occurrence about a factor of ten lower than observed near solar maximum. Thus hard X-ray microflaring appears to be an active region phenomenon, and apparently not associated with flaring of soft X-ray bright points.