ACCELERATION OF ELECTRONS OUTSIDE FLARES - EVIDENCE FOR CORONAL EVOLUTION AND HEIGHT-EXTENDED ENERGY-RELEASE DURING NOISE STORMS

The injection of suprathermal electrons in the solar corona in the abs ence of flares is witnessed by noise storm emission at decimetric and metric wavelengths. A sample of nine noise storm continua is studied b y multifrequency imaging observations. The radio observations show the frequent existence of time delays of the noise storm onsets at low fr equencies and the ubiquity of broadband fluctuations of the continuum emission on time scales of several minutes. These results agree with t he idea that noise storms are due to suprathermal electrons injected a nd trapped in extended coronal structures (or parts of such structures ). In order to carry out several bounces in such structures, the elect rons must have energies of some tens of keV. A key result is that the noise storms are systematically accompanied by a brightening of the fu ll Sun flux at soft X-ray wavelengths. The frequently comparable durat ion of soft X-ray brightenings and noise storms and occasional common features in the time profiles during the rise of the emissions point t o a physical link between the heating of the plasma in the active regi on and the injection of electrons into the overlying corona. On the ot her hand, pronounced differences in the later phases suggest that the mechanism which heats the soft X-ray emitting plasma does not simultan eously supply the electrons which radiate the noise storm emission. It is argued that these observations confirm the picture of noise storms being born in evolving systems of large-scale magnetic loops, when th e coronal magnetic field restructures itself in response to a perturba tion of the underlying active region.