X-ray emission associated with gamma-ray bursts

The energy spectra of gamma-ray bursts differ from those of black-body radiation and are similar to the thermal bremsstrahlung spectra of optically thin plasma. This could be realized if the source is located in the outer atmosphere of a neutron star. In this case, almost one half of the emitted photons hit the surface of the star. The surface of the star is heated to a temperature of the order 10⁷ K, and a dominant flux of X-rays with a black-body spectrum would be expected. The X-rays produced by this mechanism are detectable in the energy range from a few keV to 10 keV. This model is discussed in relation to the recent observations in the X-ray region at the time of gamma-ray bursts, and modifications of this model are also presented. The observation in this energy range will bring us valuable information on the nature of gamma-ray burst sources.