Spectra of GRB970228 from the transient gamma-ray spectrometer

Visible afterglow counterparts have now been detected for two GRBs (970228 and 970508) but are absent, with Lopt/Lγ ratios at least two orders of magnitude lower, for other GRBs, e.g., 970828. The causes of this variation are unknown. Any correspondence which could be discovered between the γ-ray properties of a GRB and its Lopt/Lγ would be useful, both in determining the GRB mechanisms, and in allocating resources for counterpart searches and studies. This paper presents the γ-ray spectra of GRB970228 as measured by the Transient Gamma-Ray Spectrometer and comments on characteristics of this GRB compared to others that do and do not have observable counterparts.