Deka-keV X-ray emission associated with the onset of radio noise storms

N. Crosby, N. Vilmer, Niels Lund, K.L. Klein, R. Sunyaev

    Research output: Contribution to journalJournal articleResearchpeer-review


    Radio noise storms show that suprathermal electrons (a few tens of keV) are present in the vicinity of active regions during several hours or even a few days. Where and how these electrons are energized is not yet well known. A flare-like sudden energy release in the active region is in general observed at the onset of noise storms, either as a fully developed flare or, more often, as a soft X-ray brightening without conspicuous Her signature. In order to investigate to what extent electrons energized in the active region contribute to the noise-storm emission in the overlying coronal structures, we combine radio imaging (Nancay radioheliograph) with X-ray spectral observations at photon energies of a few keV (GOES) and - for the first time - around 10 keV (WATCH/GRANAT). In two of four studied events the WATCH data show a significant excess of the deka-keV count rate above the expectation from an isothermal fit to the GOES fluxes. Although the electron population producing the deka-keV X-ray emission would be energetic enough to power the simultaneous radio noise storm, the much longer duration of the radio emission requires time-extended particle acceleration. The acceleration probably occurs in the corona overlying the X-ray emitting region, triggered by the processes which give rise to the X-ray brightenings.
    Original languageEnglish
    JournalSolar Physics
    Issue number1-2
    Pages (from-to)333-348
    Publication statusPublished - 1996


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