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 .
SN 2004aw 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 SN 1994I , 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 ^ { 56 } Ni mass is \approx 0.20 M _ { \odot } .
The ejecta mass as constrained by the models is \sim 3 - 5 M _ { \odot } , while the kinetic energy is estimated as E _ { K } \sim 3 - 6 \times 10 ^ { 51 } ergs .
The ratio E _ { K } / M _ { \textrm { ej } } , the specific energy which influences the shape of the spectrum , is therefore \approx 1 .
The corresponding zero-age main-sequence mass of the progenitor star may have been \sim 23 - 28 M _ { \odot } .
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 E _ { K } is a lower limit .
SN 2004aw 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 SN 2004aw .