Data obtained from a proportional counter on OSO-5 are examined to study variations in emission from individual solar active regions within the waveband 0.3-0.9 nm. Flux' levels are highly variable, even from the areas having a low mean emission, because increases characteristic of X-ray flares occur most of the time.It is usual to assume that the coronal levels above a plage region are heated by a fairly continuous incident energy flux (perhaps waves), while impulsive effects associated with flares add to this over localised areas. The data given here indicate that the impulsive mechanism is probably the more important in producing the total soft X-ray flux from an active region. There is also reason to believe that many of the small flares observed are not restricted to particularly localised areas. They are of the gradual rise and fall variety which probably have an extended spatial structure. It seems possible that flare heating might account for almost the entire X-ray emission throughout the active region.
A grazing incidence X-ray telescope for the study of the spatial and temporal variation of solar X-radiation in the region 0.8 to 1.6 nm, with proportional counters and pulse height wavelength discrimination, is described in some detail. An accompanying slit system covering the 0.3 to 0.9 nm region provides a more rapid coverage of flares than the spacecraft raster period would otherwise allow. Results are given illustrating the types of data being received from this instrument, which has been operating correctly for 18 months.
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