Cyclotron Absorption in Gamma-Ray Bursts Seen with GINGA

Spectral features are found in the gamma ray burst spectra from two bursts at about 20 keV, 40 keV and possibly at about 60 keV from one burst. A shift of energy of the cyclotron absorption is also observed. The interpretation of these features as the fundamental and second harmonics of the cyclotron absorption lines requires a strong magnetic field of 10 to the 12 power gauss at the absorption region of the gamma ray bursts. This supports the hypothesis that the gamma ray bursts originate near the surface of strongly magnetized neutron stars. The origin of such strong magnetic fields is discussed in the framework of current theories of evolution of neutron stars and their field decay.