SN 1998bw: The case for a relativistic shock

Abstract

SN 1998bw shot to fame by claims of association with GRB 980425. Independent of its presumed association with a GRB, this SN is unusual in its radio properties. A simple interpretation of the unusually bright radio emission leads us to the conclusion that there are two shocks in this SN: a slow moving shock containing most of the ejecta and a relativistic shock (Γ = 2) which is responsible for the radio emission. This is the first evidence for the existence of relativistic shocks in supernovae. It is quite plausible that this shock may produce high energy emission (at early times and by inverse Compton scattering). As with other supernovae, we expect radio emission at much later times powered primarily by the slow moving ejecta. This expectation has motivated us to continue monitoring this unusual SN.