4 The future: Evidence for a slow shock?

We have argued above that the radio emission in the first $\sim$100 days had its origin in a mildly relativistic shock which carries only a small amount of mass (10$^{-5}\ M_{\hbox{$\odot$}}$) and energy (10⁴⁹ erg). The bulk of the ejecta mass and energy of the SN is presumably traced by the optical photosphere. Thus, it is reasonable to expect some late-time radio emission from this slower-moving shock as it interacts with any circumstellar material. We continue to make multi-wavelength measurements toward SN1998bw at the ATCA with this in mind. Our results to date shown in Fig. 1 suggests that the power-law-like decay has persisted for at least 250 days.

  

Figure 1: The radio light curve of SN1998bw at four wavelengths (20 cm = cross, 13 cm = star, 6 cm = circle and 3 cm = square). The last measurements were made on 1998 December 30, nearly 250 days after the gamma-ray burst. On this day the 1-$\sigma$ uncertainty in these flux measurements is 0.5 mJy for 20 and 13-cm, and 0.3 mJy for 6 and 3-cm