Radio view of a broad-line Type Ic supernova ASASSN-16fp

Abstract

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 × 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 × 1047 (t/t0)0.65 erg. We determine the mass-loss rate of the progenitor star to be M˙∼(0.4−3.2)×10−5M⊙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 × 1016 cm from the explosion centre.