Interpretation of Multiple Absorption Features in a Gamma-Ray Burst Spectrum

The discovery reported by Mazets et al. in 1981 of single absorption lines at about 40 keV in the spectra of gamma-ray bursts observed by the Konus instrument implies magnetic fields ≡10¹²G and, hence, that the bursts occur on highly magnetized neutron stars. The authors report the detailed analysis of a burst (GB 880205) with double line features observed by the Ginga satellite. It is concluded that these lines are most reasonably interpreted as the first and second cyclotron harmonics in a magnetic field of ≡1.7×10¹²G with an electron column density of ≡3.6×10²²cm^-2. The narrowness of the absorption lines requires that they originate in a very cold, small area on the neutron star, probably distinct from the gamma-ray emitting region.