Diagnosing Magnetars with Transient Cooling

Transient X-ray emission, with an approximate t-0.7 decay, was observed from SGR 1900+14 over 40 days following the giant flare of 1998 August 27. We calculate in detail the diffusion of heat to the surface of a neutron star through an intense 1014-1015 G magnetic field, following the release of magnetic energy in its outer layers. We show that the power-law index, the fraction of burst energy in the afterglow, and the return to persistent emission can all be understood if the star is composed of normal baryonic material.