ACCRETION-DRIVEN MAGNETIC-FIELD DECAY IN NEUTRON-STARS

There are many arguments which imply that the evolution of the magnetic field may be substantially different for isolated neutron stars than it is for neutron stars entering close binary systems. It is likely that various processes accompanying mass exchange in binaries can influence the evolution of the magnetic field. The present paper considers the decay of the field which, before the mass-exchange stage, was confined to the neutron star crust. We concentrate on effects produced by additional heating due to accretion. The internal temperature of accreting neutron stars is rather high at high accretion rates, and, therefore, the crustal conductivity should be lower than for non-accreting stars. Besides, the temperature distribution may be strongly nonuniform for rapidly cooling neutron stars (such cooling is typical, for example, for stars with exotic matter in the core). This non-uniformity may be responsible for effective thermomagnetic processes in the crust. Both of these phenomena are taken into account in our study. Computations indicate a much more rapid field decay for accreting neutron stars. For binaries with high accretion rates (M greater than or equal to 3 X 10(-10) M. yr(-1)) and long mass-exchange stages (greater than or equal to 10(6)-10(7) yr), the field of the neutron star can be a factor similar to 10(3)-10(4) lower than that of isolated neutron stars. The suggested mechanism can provide an explanation of the low magnetic fields of many pulsars entering binaries.