The Radio and X‐Ray–Luminous Type Ibc Supernova 2003L

We present extensive radio observations of SN 2003L, the most luminous andenergetic Type Ibc radio supernova with the exception of SN 1998bw (associatedwith GRB 980425). Observations from the Very Large Array are well described bya fitting a synchrotron self-absorption model to the emission spectrum. Thismodel implies a sub-relativistic ejecta velocity, v ~ 0.2c, and a size of r ~4.3 x 10^{15} cm at t ~ 10 days. The circumstellar density is suitably fit witha stellar wind profile, n_e ~ r^{-2} and a constant mass loss rate of M_dot ~7.5 x 10^{-6} M_{solar}/year. Moreover, the magnetic field follows B ~ r^{-1}and the kinetic energy of the radio bright ejecta is roughly E ~ 10^{48} ergassuming equipartition of energy between relativistic electrons and magneticfields. Furthermore, we show that free-free absorption does not contributesignificantly to the radio spectrum, since it implies ejecta velocities whichare inconsistent with size constraints derived from Very Long Baseline Arrayobservations. In conclusion, we find that although SN 2003L has a radioluminosity comparable to that seen in SN 1998bw, it shows no evidence for asignificant amount of energy coupled to relativistic ejecta. Using SN 2003L asan example, we comment briefly on the coupling of ejecta velocity and energy inType Ibc supernovae.Comment: 32 pages, 7 figures, submitted to Ap