Evidence for thin-target X-ray emission in a small solar flare on 26 February 1972

We compare solar X-ray observations from the UCSD experiment aboard OSO-7 with high resolution energetic electron observations from the UCAL experiment on IMP-6 for a small solar flare on 26 February 1972. A proportional counter and NaI scintillator covered the X-ray energy range 5–300 keV, while a semiconductor detector telescope covered electrons from 18 to 400 keV. A series of four non-thermal X-ray spikes were observed from 1805 to 1814 UT with average spectrum dJ/d (hv) (hv)^–4.0 over the 14–64 keV range. The energetic electrons were observed at 1 AU beginning 1840 UT with a spectrum dJ/dE E ^–3.1. If the electrons which produce the X-ray emission and those observed at 1 AU are assumed to originate in a common source, then these observations are consistent with thin target X-ray production at the Sun and inconsistent with thick target production. Under a model consistent with the observed soft X-ray emission, we obtain quantitative estimates of the total energy, total number, escape efficiency, and energy lost in collisions for the energetic electrons.