The primary science investigation of the GBM will be elucidating the relation between the keV/MeV and GeV burst emission. High-energy GRB measurements from the EGRET instrument on CGRO have shown consistency with the BATSE data at lower energies, but were limited by the EGRET dead-time and the lack of sensitive measurements in an overlapping energy range. The GBM - LAT combination will provide an unprecedented 6 decades of energy with no gaps. Time-resolved spectroscopy over such a large energy range will be crucial in advancing our understanding of the mechanisms by which gamma rays are generated in GRBs.

• The canonical GRB spectral form consists of two power law segments joined smoothly at a characteristic break energy (E_break). The low-energy and high-energy power law indices are broadly distributed around -1 and -2, respectively, but the bursts with high (> hundreds keV) or ill-constrained E_break have thus far been difficult to study. The BGO detectors will provide an accurate measure of the spectrum of GRBs in the 2-20 MeV regime and will facilitate joint spectral fits to the data from the NaI, BGO detectors and the LAT.
• Correlations between low and high-energy components and burst hardness (characterized by E_break) can be probed with joint LAT/GBM data.
• In the BATSE energy range pulses in bursts tend toward a narrowing in time at higher energies, as well as a shift in the peak of pulse emission toward earlier times. With a very low dead-time for the LAT compared to EGRET burst pulses can be examined with good count statistics at high energies, and placed in context with the lower-energy emission using GBM observations.
• Indications of an X-ray excess in around 15% of GRBs can be investigated using the low-energy response of the NaI detectors.