  An analysis of the Type Ic supernova (SN) 2004aw is performed by means of
models of the photospheric and nebular spectra and of the bolometric light
curve. SN2004aw is shown not to be ``broad-lined'', contrary to previous
claims, but rather a ``fast-lined'' SN Ic. The spectral resemblance to the
narrow-lined Type Ic SN1994I, combined with the strong nebular [O I] emission
and the broad light curve, point to a moderately energetic explosion of a
massive C+O star. The ejected 56Ni mass is ~0.2 Msun. The ejecta mass as
constrained by the models is ~3-5 Msun, while the kinetic energy is estimated
as KE ~3-6 e51 ergs. The ratio KE/Mej, the specific energy which influences the
shape of the spectrum, is therefore ~1. The corresponding zero-age
main-sequence mass of the progenitor star may have been ~23-28 Msun. Tests show
that a flatter outer density structure may have caused a broad-lined spectrum
at epochs before those observed without affecting the later epochs when data
are available, implying that our estimate of KE is a lower limit. SN2004aw may
have been powered by either a collapsar or a magnetar, both of which have been
proposed for gamma-ray burst-supernovae. Evidence for this is seen in the
innermost layers, which appear to be highly aspherical as suggested by the
nebular line profiles. However, any engine was not extremely powerful, as the
outer ejecta are more consistent with a spherical explosion and no gamma-ray
burst was detected in coincidence with SN2004aw.
