Evidence for a sudden magnetic field reconfiguration in soft gamma repeater 1900+14

We report the detection of large flux changes in the persistent X-ray flux of soft gamma repeater (SGR) 1900+14 during its burst active episode in 199 8. Most notably, we find a factor of similar to 700 increase in the nonburs t X-ray flux following the August 27 flare, which decayed in time as a powe r law. Our measurements indicate that the pulse fraction remains constant t hroughout this decay. This suggests a global flux enhancement as a conseque nce of the August 27 flare rather than localized heating. While the persist ent flux has since recovered to the preoutburst level, the pulse profile ha s not. The pulse shape changed to a near sinusoidal profile within the tail of the August 27 flare (in gamma -rays), and this effect has persisted for more than 1.5 years (in X-rays). The results presented here suggest that t he magnetic field of the neutron star in SGR 1900+14 was significantly alte red (perhaps globally) during the giant flare of August 27.