Light curve and spectral evolution of the Type IIb supernova 2011fu

We present the low-resolution spectroscopic and UBVRI broad-band photometric investigations of the Type IIb supernova (SN) 2011fu, discovered in UGC 01626. The photometric follow-up of this event was initiated a few days after the explosion and covers a period of about 175 d. The early-phase light curve shows a rise, followed by steep decay in all bands, and shares properties very similar to that seen for SN 1993J, with a possible detection of the adiabatic cooling phase. Modelling of the quasi-bolometric light curve suggests that the progenitor had an extended (∼1 × 10 13 cm), low-mass (∼0.1 M ⊙ ) H-rich envelope on top of a dense, compact (∼2 × 10 11 cm), more massive (∼1.1 M ⊙ ) He-rich core. The nickel mass synthesized during the explosion was found to be ∼0.21 M ⊙ , slightly larger than that seen for other Type IIb SNe. The spectral modelling performed with synow suggests that the early-phase line velocities for H and Fe ii features were ∼16000 and ∼14000 km s −1 , respectively. Then, the velocities declined up to day +40 and became nearly constant at later epochs.