  The serendipitous observation of GRB 780506 by co-aligned gamma-ray (HEAO 1
A-4 0.02 - 6 MeV) and X-ray (HEAO 1 A-2 2-60 keV) instruments during a six hour
pointing at a blank section of the sky gave us unprecedented high
signal-to-noise X-ray spectra and light curves of a gamma-ray burst and its
afterglow. We observed two breaks in the initial spectrum, one consistent with
a peak in nu-F-nu of ~45 keV, and one below 4 keV, consistent with strong
absorption, followed by dramatic spectral variability. The initial strong
turnover below a few keV evolved into a slight excess. The spectral shape
varied widely outside low energy limits prescribed by current relativistic
shock models. Two minutes after the burst ended, HEAO 1 A-2 detected a faint
resurgence of 2-10 keV flux, rising to a peak ~seven minutes after burst onset,
followed by irregular emission with best-fit decay time of half an hour. We
estimated that this entire afterglow radiated between 3 and 30% of the >1 keV
energy radiated during the burst.
