2020MNRAS.494...84N

We present extensive radio observations of a Type Ic supernova, ASASSN-16fp. Our data represent the lowest frequency observations of the supernova beyond 1000 d with a frequency range of 0.33-25 GHz and a temporal range of ∼8-1136 d post-explosion. The observations are best represented by a model of synchrotron emission from a shocked circumstellar shell initially suppressed by synchrotron self-absorption. Assuming equipartition of energy between relativistic particles and magnetic fields, we estimate the velocity and radius of the blast wave to be v ∼ 0.15c and r ∼ 3.4 x 10¹⁵ cm, respectively, at t₀ ∼ 8 d post-explosion. We infer the total internal energy of the radio-emitting material evolves as E ∼ 0.37 x 10⁴⁷ (t/t₀)^0.65 erg. We determine the mass-loss rate of the progenitor star to be {dot}M ∼(0.4-3.2) ×10^–5 M_☉ yr^–1 at various epochs post-explosion, consistent with the mass-loss rate of Galactic Wolf-Rayet stars. The radio light curves and spectra show a signature of density enhancement in the circumstellar medium at a radius of ∼1.10 x 10¹⁶ cm from the explosion centre.