On the interpretation of gamma-ray burst continua and possible cyclotron absorption lines

Most gamma‐ray bursts have spectra which are fit by an optically thin thermal bremsstrahlung shape. We show that the small emitting volume implied by the observation of spectral features identified as cyclotron absorption lines from a 1012 Gauss field prevent thermal bremsstrahlung from providing sufficient luminosities to account for the observed fluxes unless the optical depth to Compton scattering is large. In addition, we demonstrate that complicated detector response functions can introduce artifacts which mimic absorption features below 60 keV unless the absolute gain of the detector is established and correctly applied in analysis. By comparing the continuum as observed by the Berkeley/Los Alamos ISEE‐3 gamma‐ray detector with the continuum observed by the Konus experiments we find a lack of agreement, suggesting that the gain of one of these experiments may be incorrect. Thus, a great deal of caution should be exercised in interpreting the apparent low energy features as cyclotron lines.