Study of the cyclotron feature in MXB 0656-072

Abstract

We have monitored a type II outburst of the Be/X-ray binary MXB 0656-072 in a series of pointed RXTE observations during October through December 2003. The source spectrum shows a cyclotron resonance scattering feature at 32.8 -0.4+0.5 keV, corresponding to a magnetic field strength of 3.67-0.04+0.06 × 1012 G and is stable through the outburst and over the pulsar spin phase. The pulsar, with an average pulse period of 160.4 ± 0.4 s, shows a spin-up of 0.45s over the duration of the outburst. From optical data, the source distance is estimated to be 3.9 ± 0.1 kpc and this is used to estimate the X-ray luminosity and a theoretical prediction of the pulsar spin-up during the outburst. © ESO 2006.