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 (similar to 1 x 10(13) cm), low-mass (similar to 0.1 M-circle dot) H-rich envelope on top of a dense, compact (similar to 2 x 10(11) cm), more massive (similar to 1.1 M-circle dot) He-rich core. The nickel mass synthesized during the explosion was found to be similar to 0.21 M-circle dot, 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 similar to 16 000 and similar to 14 000 km s(-1), respectively. Then, the velocities declined up to day +40 and became nearly constant at later epochs.