SN 2013df, a double-peaked IIb supernova from a compact progenitor and an extended H envelope.

Optical observations of the Type IIb SN 2013df from a few days to about 250 d after explosion are presented. These observations are complemented with UV photometry taken by SWIFT up to 60 d post-explosion. The double-peak optical light curve is similar to those of SNe 1993J and 2011fu although with different decline and rise rates. From the modelling of the bolometric light curve, we have estimated that the total mass of synthesized 56Ni in the explosion is ∼0.1 M_⊙, while the ejecta mass is 0.8-1.4 M_⊙ and the explosion energy 0.4-1.2 × 1051 erg. In addition, we have estimated a lower limit to the progenitor radius ranging from 64 to 169 R⊙. The spectral evolution indicates that SN 2013df had a hydrogen envelope similar to SN 1993J (∼0.2 M_⊙). The line profiles in nebular spectra suggest that the explosion was asymmetric with the presence of clumps in the ejecta, while the [O I] λλ6300, 6364 luminosities, may indicate that the progenitor of SN 2013df was a relatively low-mass star (∼12-13 M_⊙). [ABSTRACT FROM AUTHOR]