Gamma‐Ray–Burst Spectral Shapes from 2 keV to 500 MeV

We present three gamma-ray-burst spectra for bright bursts over very wide energy ranges. These were created from BATSE, COMPTEL, and OSSE data. The three spectra are for GRB 910503 (from 20 keV to 300 MeV), GRB 910601 (from 28 keV to 10.5 MeV), and GRB 910814 (from 103 keV to 500 MeV). A composite spectrum of 19 bright bursts is presented from 41 keV to 1.9 MeV (with no weak lines visible) for use in calculating average redshift corrections in cosmological models. Expanding fireball models with shocked synchrotron emission are predicted to have low-energy spectral slope (ν F ν ∝ ν α ) that asymptotically approaches α = 4/3 such that α should never exceed 4/3. This prediction is tested with more than 100 bright bursts with BATSE and Ginga data. Over 90% of the bursts have spectral slopes in agreement with this prediction. For only one burst (GRB 870303, which has reported cyclotron lines) can a strong case be made that the slope violates the model limit, and then only from 2-5 keV.