SN 2016B a.k.a. ASASSN-16ab: a transitional Type II supernova

Abstract

We present photometry, polarimetry, and spectroscopy of the Type II supernova ASASSN-16ab/SN 2016B in PGC 037392. The photometric and spectroscopic follow-up commenced about 2 weeks after shock breakout and continued until nearly 6 months. The light curve of SN 2016B exhibits intermediate properties between those of Type IIP and IIL. The early decline is steep (1.68 ± 0.10 mag 100 d<SUP>-1</SUP>), followed by a shallower plateau phase (0.47 ± 0.24 mag 100 d<SUP>-1</SUP>). The optically thick phase lasts for 118 d, similar to Type IIP. The <SUP>56</SUP>Ni mass estimated from the radioactive tail of the bolometric light curve is 0.082 ± 0.019 M<SUB>☉</SUB>. High-velocity component contributing to the absorption trough of H α and H β in the photospheric spectra are identified from the spectral modelling from about 57-97 d after the outburst, suggesting a possible SN ejecta and circumstellar material interaction. Such high-velocity features are common in the spectra of Type IIL supernovae. By modelling the true bolometric light curve of SN 2016B, we estimated a total ejected mass of ∼15 M<SUB>☉</SUB>, kinetic energy of ∼1.4 foe, and an initial radius of ∼400 R<SUB>☉</SUB>.