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Session 45 - New Insights on X-ray Binaries.
Display session, Wednesday, June 11
South Main Hall,

[45.01] Optical/IR Observations of the Low-Mass X-Ray Binaries GX 1+4 and 4U 1626-67

D. Chakrabarty (MIT), P. Roche (U. Sussex), M. H. van Kerkwijk (IoA/Cambridge), J. E. Larkin (U. Chicago)

We present extensive optical and IR observations of the symbiotic low-mass X-ray binary GX 1+4/V2116 Oph, which consists of a 2-min X-ray pulsar accreting from an M6 III giant. This is the only known symbiotic system definitely known to contain a neutron star. We discuss the evolutionary status of the donor, and argue that the binary period must be longer than 100 days, making GX 1+4 the only known LMXB with Porb > 10 d. We also show that the dense emission line nebula enshrouding the binary is powered by ultraviolet radiation from an accretion disk. Infrared spectroscopy shows evidence for a relatively fast wind from the M giant.

Rapid UBVRI photometry of the ultracompact LMXB pulsar 4U 1626-67 has detected optical pulsations in all five bands, at the same period as the 7.66 s X-ray pulsations. These observations also detect the weaker persistent sideband originally reported by Middleditch et al., corroborating the 42-min binary period they proposed. In addition, these optical observations have detected a 0.048 Hz quasi-periodic oscillation previously observed in X-rays. This marks the first detection of an optical QPO from an X-ray pulsar system.

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