This SN was discovered by Stefano Moretti
(IAUC 8413) on September 22, 2004, and was absent on September 15,
2004, so discovered shortly after explosion.
The host galaxy
is at z=0.000160 (NED).
The same IAUC also suggests it is of type II, confirmed later by Filippenko and co.
This paper by Li and collaborators, discusses the progenitor of
SN 2004et, and also provides light curves, spectra and a photometric calibration.