Microwave Spectral Evolution of Solar Flares

[摘要] Weanalyzethetimeevolutionofmicrowavespectralindicesfor103solarflaresobservedbyNobeyamaRadioPolarimeters(NoRP)between1998and2005.Themicrowavespectralindex,$$gamma(t)$$,isderivedfromthefluxspectralindex,$$delta(t)$$.Weassumeafluxfrequencydependenceoftheform$$S(u,t)=F_0u^{delta(t)}$$intheopticallythinpart,i.e.,abovetheturnoverfrequency,$$f_{max}$$.Here,$$f_{max}$$isdefinedasthefrequencywiththemaximumfluxamongsixdiscretefrequencies(i.e.,1,2,3.75,9.4,17,and35 GHz).BasedonNoRPobservations,wefindtwotypicaltypesofsolarflareswithvariousmicrowavespectralbehavior.TypeIdisplaysasoft–hard–softpattern,whilethetypeIIflarefollowsasoft–hard–harderbehaviorintherise–peak–decayphasesat35 GHz.Ourstatisticalresultsofmicrowaveflaresconfirmpreviousfindings.MostmicrowaveflaresappeartobeoftypeII(91outofthepresentsamples),whichisdifferentfromthehardX-rayflaresdominatedbythesoft–hard–softproperty.Suchadifferenceisanobservationalconstraintforelectronaccelerationandtransporttheoriesinflaremodels.

[学科分类] 天文学(综合)

[关键词] "Sun: activity";"Sun: flares";"Sun: radio radiation"