P. A. Jenke, M. H. Finger, C. A. Wilson-Hodge, A. Camero-Arronz
OAO 1657-415 is an eclipsing X-ray binary wind-fed pulsar that has exhibited
smooth spin-up/spin-down episodes and has undergone several torque reversals
throughout its long history of observation. We present a frequency history
spanning nearly 19 years of observations from the Burst and Transient Source
Experiment (CGRO/BATSE) and from the Gamma-Ray Burst Monitor (Fermi/GBM). The
analysis suggests two modes of accretion: one resulting in steady spin-up
during which we believe a stable accretion disk is present and one that results
in what appears to be a random walk in spin frequency where an unstable
accretion disk forms alternating in direction ("flip flop"). Orbital elements
of the pulsar system are determined at several intervals throughout this
history. With these ephemerides, statistically significant orbital decay
($\dot{P}/P =(-3.40 \pm0.15)\times10^{-6}\ \mathrm{yr^{-1}}$) is established
suggesting a transition between wind-fed and disk-mediated accretion.
View original:
http://arxiv.org/abs/1112.5190
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