A fundamental test of the fireball model for GRBs

The most extreme GammaRay Bursts (GRBs) radiate equivalent isotropic energiesclose to 1E54 erg in electromagnetic radiation; energies which cannot beaccommodated in corecollapse models. Thus GRBs are thought to be narrowlybeamed, which should give rise to an achromatic light curve break as the outflowslows. However, observations have not been able to securely identify Xray lightcurve breaks leading to serious concerns about the total energetics which mayundermine the entire GRB paradigm. Thus we seek observations totalling 120 ks totest for the absence of such breaks in the Xray light curves of two furtherhighly energetic GRBs, continuing our campaign to use the most extreme sourcesin the GRB population to reexamine the widely accepted GRB corecollapse models. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]