Structural development of the X-ray limb flare of 30 April 1980

We describe the development of the limb flare of 30 April 1980, 20:20 UT, as observed by the Hard X-ray Imaging Spectrometer (HXIS) aboard the Solar Maximum Mission (SMM). It consisted of a short-lived bright nucleus (FWHM < 10,000 km), just inside the Sun's limb; a longer lasting tongue, extending to a height of 30,000 km, and a more complicated feature, approximately situated at the Sun's limb. The tongue was a pre-existing magnetic structure that started emitting X-rays only a few seconds after the bright nucleus, and which had a slightly higher temperature than the nucleus; its X-ray emission may be caused by electrons escaped from the nucleus.