  Gamma-ray bursts (GRBs) are short, intense flashes of soft gamma-rays coming
from the distant Universe. Long-duration GRBs (those lasting more than ~2 s)
are believed to originate from the deaths of massive stars, mainly on the basis
of a handful of solid associations between GRBs and supernovae. GRB 060614, one
of the closest GRBs discovered, consisted of a 5-s hard spike followed by
softer, brighter emission that lasted for ~100 s. Here we report deep optical
observations of GRB 060614 showing no emerging supernova with absolute visual
magnitude brighter than M_V = -13.7. Any supernova associated with GRB 060614
was therefore at least 100 times fainter, at optical wavelengths, than the
other supernovae associated with GRBs. This demonstrates that some long-lasting
GRBs can either be associated with a very faint supernova or produced by
different phenomena.
