On the nature of gamma-ray burst spectra

Abstract

The recent discovery of low-energy absorption features in the spectra of gamma-ray bursts (GRBs) reported by Murakami et al. (1988) is discussed in the context of a new model for gamma-ray emission in isolated neutron-star sources. It is shown that the whole GRB spectrum may be due to irradiation of a reprocessing and reflecting boundary near a source of power-law gamma radiation. In this picture, the gamma-rays originate far above the surface of a magnetized neutron star where attenuation of the spectrum by pair production is minimal. The surface layers of the neutron star absorb a fraction of the gamma-ray energy and reflect some of the gamma-rays. The resultant spectrum is comprised of a power law at high energy, a steep component at intermediate energy, and a thermal component at low energy. There is a slight enhancement of the gamma-ray flux near E0 that may be the cause of the apparent d(-)d(+) annihilation line seen in some bursts. 27 references.