The Radio and X-Ray-Luminous Type Ibc Supernova 2003L

We present extensive radio observations of SN 2003L, the most luminous and energetic Type Ibc radio supernova with the exception of SN 1998bw (associated with GRB 980425). Observations from the Very Large Array are well described by fitting a synchrotron self-absorption model to the emission spectrum. This model implies a subrelativistic ejecta velocity, v̄ ≈ 0.2c, and a size of r ≈ 4.3 × 1015 cm at t ≈ 10 days. The circumstellar density is suitably fitted with a stellar wind profile, ne ∝ r-2 cm-3 and a constant mass-loss rate of Ṁ ≈ 7.5 × 10-6 M☉ yr-1. Moreover, the magnetic field follows B ∝ r-1 and the kinetic energy of the radio-bright ejecta is roughly E ≈ 1048 ergs assuming equipartition of energy between relativistic electrons and magnetic fields. Furthermore, we show that free-free absorption does not contribute significantly to the radio spectrum, since it implies ejecta velocities that are inconsistent with size constraints derived from Very Long Baseline Array observations. In conclusion, we find that although SN 2003L has a radio luminosity comparable to that seen in SN 1998bw, it shows no evidence for a significant amount of energy coupled to relativistic ejecta. Using SN 2003L as an example, we comment briefly on the coupling of ejecta velocity and energy in Type Ibc supernovae.