We examine 48 Swift/UVOT long Gamma-ray Burst light curves and find a
correlation between the logarithmic luminosity at 200 s and average decay rate determined
from 200 s onwards, with a Spearman rank coefficient of −0.58 at a significance of 99.998%
(4.2σ). We determine the
log L200s − α > 200s correlation to be
intrinsic and discuss two possible causes: there is a property of the central engine,
outflow or external medium that effects the rate of energy release so that the bright
afterglows release their energy more quickly and decay faster than the fainter afterglows;
alternatively, the observers viewing angle may produce the correlation, with observers at
large viewing angles observing fainter and slower decaying light curves.