ASASSN-16fp (SN 2016coi): a transitional supernova between Type Ic and broad-lined Ic

We present results based on a well-sampled optical (UBVRI) and ultraviolet (Swift/UVOT) imaging, and low-resolution optical spectroscopic follow-up observations of the nearby Type Ic supernova (SN) ASASSN-16fp (SN 2016coi). The SN was monitored during the photospheric phase (-10 to +33 d with respect to the B-band maximum light). The rise to maximum light and early post-maximum decline of the light curves are slow. The peak absolute magnitude (M_V = -17.7 ± 0.2 mag) of ASASSN-16fp is comparable with broad-lined Ic SN 2002ap, SN 2012ap and transitional Ic SN 2004aw but considerably fainter than the gamma-ray burst/X-ray flash associated SNe (e.g. SN 1998bw, 2006aj). Similar to the light curve, the spectral evolution is also slow. ASASSN-16fp shows distinct photospheric phase spectral lines along with the C II features. The expansion velocity of the ejecta near maximum light reached ∼16 000 km s^-1 and settled to ∼8000 km s^-1, ∼1 month post-maximum. Analytical modelling of the quasi-bolometric light curve of ASASSN-16fp suggests that ∼0.1 M_⊙ ⁵⁶Ni mass was synthesized in the explosion, with a kinetic energy of 6.9^{+1.5}_{-1.3} × 10⁵¹ erg and total ejected mass of ∼4.5 ± 0.3 M_⊙.