Temporal behaviour of GRB afterglow light curve is derived for the case where
the electron energy distribution is relatively flat, with the power-law index p
lying between 1.0 and 2.0. It is shown that the expected behaviour will be the
same as that for p>2.0 if the upper cutoff in the electron energy distribution
evolves in direct proportion to the bulk Lorentz factor of the blast wave.Comment: 8 pages, uses basi.sty (included). Revised according to referees'
comments. Added discussion on Dai & Cheng (2001) astro-ph/0105055. Accepted
for publication in Bull. Astr. Soc. Indi
