We present optical photometry and spectroscopy of the Type IIP supernova SN 2004et that occurred in the nearby galaxy NGC 6946. The observations span a time range of 8-541 d after explosion. The late time bolometric luminosity and the Hα luminosity in the nebular phase indicate that 0.06 ± 0.02 M of 56 Ni was synthesized during the explosion. The plateau luminosity, its duration and the expansion velocity of the supernova at the middle of the plateau indicate an explosion energy of E exp = 1.20 +0.38 −0.30 × 10 51 erg. The late time light curve and the evolution of the [O I] and Hα emission-line profiles indicate the possibility of an early dust formation in the supernova ejecta. The luminosity of [O I] 6300, 6364 Å doublet, before the dust formation phase, is found to be comparable to that of SN 1987A at similar epochs, implying an oxygen mass in the range 1.5-2 M , and a main-sequence mass of 20 M for the progenitor.

Aims. We present multiwavelength observations of the gamma-ray burst GRB 051028 detected by HETE-2 in order to derive its afterglow emission parameters and to determine the reason for its optical faintness when compared to other events. Methods. Observations were taken in the optical (2.0 m Himalayan Chandra Telescope, 1.34 m Tautenburg, 4.2 m William Herschel Telescope) and in X-rays (Swift/XRT) between 2.7 h and ∼10 days after the onset of the event.Results. The data can be interpreted by collimated emission in a jet with a typical value of p = 2.4 which is moving in a homogeneous interstellar medium and with a cooling frequency ν c still above the X-rays at 0.5 days after the burst onset. GRB 051028 can be classified as a "gray" or "potentially dark" GRB. On the basis of the combined optical and Swift/XRT data, we conclude that the reason for the optical dimness is not extra absorption in the host galaxy, but rather the GRB taking place at high-redshift. We also notice the very striking similarity with the optical lightcurve of GRB 050730, a burst with a spectroscopic redshift of 3.967, although GRB 051028 is ∼3 mag fainter. We suggest that the bumps could be explained by multiple energy injection episodes and that the burst is intrinsically faint when compared to the average afterglows detected since 1997. The non-detection of the host galaxy down to R = 25.1 is also consistent with the burst arising at high redshift, compatible with the published pseudo-z of 3.7 ± 1.8.