Torque reversal and orbital profile of X-ray pulsar OAO 1657?415

ABSTRACT OAO 1657?415 is an atypical supergiant X-ray binary among wind- and disc-fed systems, showing alternate spin-up/spin-down intervals lasting of the order tens days. We study different torque states based on spin history monitored by Fermi/Gamma-Ray Burst Monitor, together with fluxes from Swift/Burst Alert Telescope (BAT) Monitor All-sky Image/Gas Slit Camera. Its frequency derivatives are well correlated Swift/BAT during rapid spin-up episodes, anticorrelated spin-down not in between. The orbital profile episodes reduced a factor 2 around phases 0.2 0.8 compared to that episodes. hardness ratio also lower than close mid-eclipse, implying there more material between neutron star observer for these phases. These results indicate state connected flow scale support retrograde/prograde disc accretion scenario spin-down/spin-up reversal.