  We report on the X-ray spectrum of the 401 Hz X-ray pulsar and type I burst
source SAX J1808.4-3658, during its 1998 April/May hard outburst. The
observations were made with RXTE over a period of three weeks. The spectrum is
well-described by a power law with photon index 1.86+/-0.01 that is
exponentially cut off at high energies. Excess soft emission above the power
law is present as well as a weak Fe-K line. This is the first truly
simultaneous broad-band (2.5-250 keV) spectrum of a type I burst source in the
hard state. The spectrum is consistent with other hard state burster spectra
which cover either only the soft (1-20 keV) or hard (>20 keV) bands, or cover
both, but not simultaneously. The cut-off power law resembles black hole
candidates (BHCs) in their low states, observed with RXTE. We compare the SAX
J1808.4-3658 spectrum to three BHCs and find that the power law is somewhat
softer. This suggests that the photon index may provide a way to distinguish
between low state emission from Galactic black holes and type I bursters.
