Change in Accretion Torque in the Binary Accreting Pulsar 4U 1626-67

Abstract

We describe two years of BATSE observations of the 7.66 s accreting pulsar 4U 1626-6i. Power spectral analysis and period folding techniques with the 1.024 s resolution DISCLA data froru the Large Area Detectors (LADs) have provided nearly continuous monitoring of 4U 1626-6i in the 20-60 ke V range. The long term frequency history of the source shows nearly constant spin-down at a rate of f ~ -7.4 x 10^(-13) s^(-2) , in contrast to the continuous spin-up {with f ~ 8.5 x^(-13) t 3 s- 2) observed previously. We discuss the implications of these results for accretion torque theories and compare this behavior to that of GX 1+4.

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