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Solar flares observed in the 200-400 GHz radio domain may exhibit a slowlyvarying and time-extended component which follows a short (few minutes)impulsive phase and which lasts for a few tens of minutes to more than onehour. The few examples discussed in the literature indicate that suchlong-lasting submillimeter emission is most likely thermal bremsstrahlung. Wepresent a detailed analysis of the time-extended phase of the 2003 October 27(M6.7) flare, combining 1-345 GHz total-flux radio measurements with X-ray,EUV, and H{\alpha} observations. We find that the time-extended radio emissionis, as expected, radiated by thermal bremsstrahlung. Up to 230 GHz, it isentirely produced in the corona by hot and cool materials at 7-16 MK and 1-3MK, respectively. At 345 GHz, there is an additional contribution fromchromospheric material at a few 10^4 K. These results, which may also apply toother millimeter-submillimeter radio events, are not consistent with theexpectations from standard semi-empirical models of the chromosphere andtransition region during flares, which predict observable radio emission fromthe chromosphere at all frequencies where the corona is transparent.

Origin of the submillimeter radio emission during the time-extended phase of a solar flare