Abstract
Soft Gamma Repeaters (SGRs) have been proposed to be neutron stars with extremely strong magnetic fields of > 5 x 1014 G. The spectra of SGR 1806-20 and the initial spike of the March 5 event can be fitted by a photon-splitting modified spectrum under such a strong magnetic field. A moderate beaming pattern is needed for the emission producing the initial spike of the March 5 event, and the strength of its magnetic field is not well constrained by spectral fitting. An extended emission region over the whole stellar surface is preferred for SGR 1806-20 rather than a localized equatorial region. The intrinsic emission of SGR 1806-20 should be nearly isotropic. The magnetic field near the surface of SGR 1806-20 should be > 10 Be (Be = 4.4 x 1013 G) and its GM/c~R is > 0.25.