  We observed the newly discovered Galactic jet source XTE J0421+560 (= CI Cam)
with ASCA from 1998 April 3.3 to April 4.1 (UT), three days after the beginning
of the outburst. The X-ray intensity in the 1-10 keV band gradually decreased
with an e-folding time of about 30 hours; the decline was accompanied by
spectral softening. Two flare-like intensity enhancements were detected below 1
keV. We could fit the average spectrum above 0.8 keV with a two-temperature
model (5.7 and 1.1 keV) of thermal emission from an optically thin
ionization-equilibrium plasma. The broad iron-K profile, however, requires an
extra emission line at 6.4 keV, or Doppler broadening (or both). The former can
be explained in terms of reflection from cold matter, while the latter can be
attributed to emission from the twin jets. In both cases, the time evolution of
the emission measure and of the temperature are difficult to explain by
emission from a single plasma, suggesting that heat input and/or injection of
material was occurring during the outburst.
