Spectra of GRB 970228 from the Transient Gamma-Ray Spectrometer

Abstract

Visible afterglow counterparts have now been detected for two GRBs (970228 and 970508) but are absent, with $L_{opt}/L_{\gamma }$ 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 gamma-ray properties of a GRB and its $L_{opt}/L_{\gamma }$ would be useful, both in determining the GRB mechanisms, and in allocating resources for counterpart searches and studies. This paper presents the gamma-ray spectra of GRB 970228 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.

arXiv commentTo appear in "Gamma-Ray Bursts", Proceedings of the 4th Huntsville Symposium, 1997, eds. C. Meegan, R. Preece, and T. Koshut, 5 pages, LaTeX (aipproc.sty incl.), 3 figs. (epsfig.sty)