  We report the variable X-ray emission from BL Lacertae detected in the ASCA
ToO observation conducted during the EGRET and RXTE pointings, coincident with
the 1997 July outburst. The source showed a historically high state of X-ray,
optical, and gamma-ray emission, with its 2-10 keV flux peaking at ~3.3 E-11
erg/cm2/s. This is more than 3 times higher than the value measured by ASCA in
1995. We detected two rapid flares which occured only in the soft X-ray band,
while the hard X-ray flux also increased, but decayed with a much longer time
scale. Together with the requirement of a very steep and varying power law
dominating the soft X-ray band in addition to the hard power law, we suggest
that both the high energy end of the synchrotron spectrum and the hard inverse
Compton spectrum were visible in this source during the outburst. We discuss
the possible origins of the observed variability time scales, and interpret the
short time scales of the soft X-ray variability as reflecting the size of the
emission region.
