Simulation results for hardness ratio measurements with the GRM instrument (exposure time 10⁵   s) for our two explosion models. On the left, a source distance of 1   Mpc is assumed, and the right figure shows the results for a source distance of 5   Mpc. Taking the sensitivity limits of GRIPS into account, here denotes the energy band from 0.2   MeV to 0.4   MeV. The solid lines show the results of ideal measurements without background fluctuations and statistical errors.