We present ground-based and Hubble Space Telescope optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z = 0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broad-band spectral energy distributions (SEDs) of the OT resemble those of local Type Ic supernovae (SNe). For GRB 090618, the dense sampling of our optical observations has allowed us to detect well-defined bumps in the optical LCs, as well as a change in colour, that are indicative of light coming from a core-collapse SN. The accompanying SNe for both events are individually compared with SN1998bw, a known GRB supernova, and SN1994I, a typical Type Ic supernova without a known GRB counterpart, and in both cases the brightness and temporal evolution more closely resemble SN1998bw. We also exploit our extensive optical and radio data for GRB 090618, as well as the publicly available Swift-XRT data, and discuss the properties of the afterglow at early times. In the context of a simple jet-like model, the afterglow of GRB 090618 is best explained by the presence of a jet-break at t − t o > 0.5 d. We then compare the rest-frame, peak V-band absolute magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large sample of local Type Ibc SNe, concluding that, when host extinction is considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from the peak magnitudes of non-GRB/XRF SNe.

Optical UBVRI photometry and medium‐resolution spectroscopy of the Type Ib supernova SN 2009jf, during the period from ∼ −15 to +250 d, with respect to the B maximum are reported. The light curves are broad, with an extremely slow decline. The early post‐maximum decline rate in the V band is similar to SN 2008D; however, the late‐phase decline rate is slower than other Type Ib supernovae studied. With an absolute magnitude of MV=−17.96 ± 0.19 at peak, SN 2009jf is a normally bright supernova. The peak bolometric luminosity and the energy deposition rate via the 56Ni →56Co chain indicate that ∼0.17+0.03−0.03 M⊙ of 56Ni was ejected during the explosion. The He i 5876 Å line is clearly identified in the first spectrum of day ∼ −15, at a velocity of ∼16 000 km s−1. The [O i] 6300–6364 Å line seen in the nebular spectrum has a multipeaked and asymmetric emission profile, with the blue peak being stronger. The estimated flux in this line implies that ≳1.34 M⊙ oxygen was ejected. The slow evolution of the light curves of SN 2009jf indicates the presence of a massive ejecta. The high expansion velocity in the early phase and broader emission lines during the nebular phase suggest it to be an explosion with a large kinetic energy. A simple qualitative estimate leads to the ejecta mass of Mej= 4–9 M⊙ and kinetic energy EK= 3–8 × 1051 erg. The ejected mass estimate is indicative of an initial main‐sequence mass of ≳20–25 M⊙.

We present a theoretical model for Type Ib supernova (SN) 2006jc. We calculate the evolution of the progenitor star, hydrodynamics and nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC). The synthetic bolometric LC is compared with the observed bolometric LC constructed by integrating the UV, optical, near-infrared (NIR), and mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as 40M ⊙ on the zero-age main-sequence. The star undergoes extensive mass loss to reduce its mass down to as small as 6.9M ⊙ , thus becoming a WCO Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which amorphous carbon grains can be formed. This could explain the NIR brightening and the dust feature seen in the MIR spectrum. We suggest that the progenitor of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss and such massive stars are the important sites of dust formation. We derive the parameters of the explosion model in order to reproduce the bolometric LC of SN 2006jc by the radioactive decays: the ejecta mass 4.9M ⊙ , hypernova-like explosion energy 10 52 ergs, and ejected 56 Ni mass 0.22M ⊙ . We also calculate the circumstellar interaction and find that a CSM with a flat density structure is required to reproduce the X-ray LC of SN 2006jc. This suggests a drastic change of the mass-loss rate and/or the wind velocity that is consistent with the past luminous blue variable (LBV)-like event.

Photometric and spectral evolution of the Type Ic supernova SN 2007ru until around 210 days after maximum are presented. The spectra show broad spectral features due to very high expansion velocity, normally seen in hypernovae. The photospheric velocity is higher than other normal Type Ic supernovae. It is lower than SN 1998bw at ∼ 8 days after the explosion, but is comparable at later epochs. The light curve evolution of SN 2007ru indicates a fast rise time of 8±3 days to B band maximum and post-maximum decline more rapid than other broad-line Type Ic supernovae. With an absolute V magnitude of −19.06, SN 2007ru is comparable in brightness with SN 1998bw and lies at the brighter end of the observed Type Ic supernovae. The ejected mass of 56 Ni is estimated to be ∼ 0.4M ⊙ . The fast rise and decline of the light curve and the high expansion velocity suggest that SN 2007ru is an explosion with a high kinetic energy/ejecta mass ratio (E K /M ej ). This adds to the diversity of Type Ic supernovae. Although the early phase spectra are most similar to those of broadline SN 2003jd, the [OI] line profile in the nebular spectrum of SN 2007ru shows the singly-peaked profile, in contrast to the doubly-peaked profile in SN 2003jd. The singly-peaked profile, together with the high luminosity and the high expansion velocity, may suggest that SN 2007ru could be an aspherical explosion viewed from the polar direction. Estimated oxygen abundance 12 + log(O/H) of ∼8.8 indicates that SN 2007ru occurred in a region with nearly solar metallicity.