The Orbital Period of the Accreting Pulsar GX 1+4

Abstract

We report strong evidence for a ∼304 day periodicity in the spin history of the accretion-powered pulsar GX 1ϩ4 that is most probably associated with the orbital period of the system. We have used data from the Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory to show a clear periodic modulation of the pulsar frequency from 1991 to date, in excellent agreement with the ephemeris proposed by Cutler, Dennis, & Dolan in 1986. Our results indicate that the orbital period of GX 1ϩ4 is days, making it the 303.8 ‫ע‬ 1.1 widest known low-mass X-ray binary system by more than 1 order of magnitude and putting this long-standing question to rest. A likely scenario for this system is an elliptical orbit in which the neutron star decreases its spin-down rate (or even exhibits a momentary spin-up behavior) at periastron passages due to the higher torque exerted by the accretion disk onto the magnetosphere of the neutron star. These results are not inconsistent with either the X-ray pulsed flux light curve measured by BATSE during the same epoch or the X-ray flux history from the All-Sky Monitor on board the Rossi X-Ray Timing Explorer.

A Suzaku View of Accretion-powered X-Ray Pulsar GX 1+4

“…This value is comparable to the size of the orbit (∼ 10 13 cm) for the earlier reported period of 300 d (Cutler et al 1986;Pereira et al 1999). If the fluorescent lines are emitted from such a large region, the observed time variation should be smeared with the light crossing time of the region, which is more than 100 s for the size of 3.4×10 12 cm.…”

“…Optical counterpart of the neutron star was classified as an M5 III spectral type giant star in a rare type of symbiotic system (Shahbaz et al 1996;Chakrabarty & Roche 1997). Based on variations of the pulse period of the neutron star during spin-up phase measured with the high-energy X-ray spectrometer onboard OSO-8, Cutler et al (1986) proposed an orbital period of approximately 304 d. Pereira et al (1999) claimed confirmation of this period using BATSE observation in 1990s when the source was in spin-down phase. On the other hand, using infrared measurement of radial velocity of the M giant, the orbital period was derived to be 1161 d by Hinkle et al (2006).…”

Variability of the symbiotic X-ray binary GX 1+4

“…In the case of elliptical orbit the period of binary can be estimated thanks to enhancement of mass transfer at periastron. Using this technique Cutler et al (1986) and Pereira et al (1999) found evidence of a ∼304d period in X-ray observations. On the other hand no evidence of orbital period was found in Swift Burst Alert Telescope (BAT) and the Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) observations (Corbet et al 2008).…”

A catalogue of symbiotic stars

“…077=H 2−5 IR-type D - [198],S - [18,137]. 084=V2116 Oph Orbital period of 303.8 days is derived from the spin changes of the X-ray pulsar companion [247,56]. 088=M 1−21 V K magnitudes -close and fainter companion also measured.…”