LIMITS TO DERIVED FLARE PROPERTIES USING ESTIMATES FOR THE BACKGROUND FLUXES - EXAMPLES FROM GOES

Most methods for deriving the temperature and emission measure during solar and stellar flares require subtraction of the correct amount of background, nonflare flux. If no subtraction is done, one implicitly averages over all emitting sources within the field of view, which can give derived properties that differ from the properties of the flare itself. At the other extreme, subtraction of the entire preflare flux avoids averaging over other sources but implicitly assumes that the flare plasma did not emit outside of flaring times. This, then, requires that either the temperature or the emission measure of the flare plasma was zero before and after the flare, which is not expected. A new method is presented for deriving the limits to the background fluxes that should be subtracted from the total flux to give the flare flux. This method is based on the assumption that the temperature, emission measure, and fluxes should all increase at the start of the flare. In addition, the flaring active region is assumed to be hotter than the average of all background sources. Solar soft X-ray fluxes observed by the disk-integrating X-ray sensors on the GOES spacecraft during the 1986 February 3 and 1987 October 22 flares are used to demonstrate this method. Results from this method show that the flare properties do not always lie between those derived by either using or subtracting the entire preflare flux. The addition of a third limit, found by subtracting the long-wavelength and using the short-wavelength preflare fluxes, is necessary to bound the flare properties.