Highly magnetized neutron star in GX 301-2

Abstract

The angular momentum of matter accreting onto the neutron star produces significant spin-up torque. Effective braking mechanism must exist to balance it in order to explain the existence of slowly-rotating X-ray pulsars. The efficiency of breaking steeply decreases with the rotational frequency and the magnetic field strength. Slowly rotating sources like GX 301-2 must therefore be highly magnetized (B~10¹⁴G), which is in apparent contradiction with the field estimate from the position of a cyclotron line observed in GX 301-2 (B~3×10¹²G). We suggest that this contradiction may be resolved if the line forming region resides in an accretion column of significant height [1]. We investigate this hypothesis using INTEGRAL and BATSE observations and conclude, that the field at the top of the column shall be weak enough to explain the observed cyclotron line energy.