The result is a shallow power-law slope with an exponential cut-off at E0 (the peak energy output of the source), with a steeper power-law fall-off at high energies.
In addition to their smaller t90 values, short-duration GRBs also exhibit harder spectra (i.e., more high-energy photons relative to low-energy photons). This can be seen either by examining the distribution of E0 values (which are systematically higher for short-duration GRBs, or by a more simple duration vs. hardness ratio phase space plot (Figure 4).
While a two-parameter (duration and spectral hardness) classification of GRBs has proven relatively effective at discriminating between different progenitor systems, it is worthwhile emphasizing that in reality the distinction can often be less clear. First, there is clearly overlap in the populations (Figure 3), and so some GRBs with t90 < 2 s will actually fall into the long-soft category. But more importantly, a number of what we consider "short" GRBs actually have a light curve with a short, hard spike, but also display longer-lived emission at higher energies as well. The most dramatic known example, shown in Figure 5, is GRB080503 \cite{Perley2009}, where the long tail actually contains a higher fluence than the short initial spike. Such events are now paradoxically referred to "short GRBs with extended emission", a mouthful if ever there was one.