On the persistent X-ray emission from the soft gamma-ray repeaters
  It is suggested that the persistent X-ray emission from the soft gamma-ray repeaters is the thermal radiation of neutron stars which is enhanced by a factor of 10 or more due to the effect of a very strong magnetic field on the thermal structure of the neutron star envelope. For the thermal luminosity to be consistent with the persistent X-ray luminosity, the field strength at the neutron star surface has to be of the order of $10^{15}$ G. If it is confirmed that the soft gamma-ray repeaters are neutron stars with negligible accretion, then the presence of such a strong magnetic field is inevitable. 
V.V. Usov