A Failed Gamma-Ray Burst with Dirty Energetic Jets Spirited Away? New Implications for the GRB-SN Connection from Supernova 2002ap

Abstract

(Abridged) SN 2002ap is an interesting event with broad spectral features like the famous SN 1998bw / GRB 980425. Here we examine the recently proposed jet hypothesis from SN 2002ap by a spectropolarimetric observation. We show that jets should be moving at about 0.23c with a jet kinetic energy of ~5 x 10^{50} erg, a similar energy scale to the GRB jets. The weak radio emission from SN 2002ap has been used to argue against the jet hypothesis, but we show that this problem can be avoided. However, the jet cannot be kept ionized because of adiabatic cooling without external photoionization or heating source. We found that only the radioactivity of 56Ni is a possible source, indicating that the jet is formed and ejected from central region of the core collapse. Then we point out that the jet will eventually sweep up enough interstellar medium and generate shocks in a few to 10 years, producing strong radio emission that can be spatially resolved, giving us a clear test for the jet hypothesis. Discussions are given on possible implications for the GRB-SN connection in the case that the jet is real. We suggest existence of two distinct classes of GRBs from similar core-collapse events but by completely different mechanisms. Cosmologically distant GRBs (~10^{50} erg) are collimated jets generated by central activity of core collapses. SN 2002ap could be a failed GRB of this type with a large baryon load. On the other hand, much less energetic ones like GRB 980425 are rather isotropic, which may be produced by hydrodynamical shock acceleration at the outer envelope. We propose that the radioactive ionization for the SN 2002ap jet may give a new explanation also for the X-ray line features often observed in GRB afterglows.