  We present an update of our systematic analysis of all Gamma-Ray Burst (GRB)
afterglow data, now published through the end of 2004, in an attempt to detect
the predicted supernova light component. We fit the observed photometric light
curves as the sum of an afterglow, an underlying host galaxy, and a supernova
component. The latter is modeled using published UBVRI light curves of SN
1998bw as a template. The total sample of afterglows with established redshifts
contains now 29 bursts (GRB 970228 - GRB 041006). For 13 of them a weak
supernova excess (scaled to SN 1998bw) was found. In agreement with our earlier
result (Zeh et al. 2004) we find that also in the updated sample all bursts
with redshift < 0.7 show a supernova excess in their afterglow light curves.
The general lack of a detection of a supernova component at larger redshifts
can be explained with selection effects. These results strongly support our
previous conclusion based on all afterglow data of the years 1997 to 2002 that
in fact all afterglows of long-duration GRBs contain light from an associated
supernova.
