Evidence for a 304-day orbital period for GX 1+4

Braga, Joa˜o; Pereira, Marildo G.; Jablonski, Francisco J.
April 2000
AIP Conference Proceedings;2000, Vol. 510 Issue 1, p188
Academic Journal
In this paper we report strong evidence for a ∼304-day periodicity in the spin history of the accretion-powered pulsar GX 1+4 that is very likely to be a signature of the orbital period of the system. Using BATSE public-domain data, we show a highly-significant periodic modulation of the pulsar frequency from 1991 to date which is in excellent agreement with the ephemeris proposed by Cutler, Dennis & Dolan in 1986 [1], which were based on a few events of enhanced spin-up that occurred during the pulsar’s spin-up era in the 1970s. Our results indicate that the orbital period of GX 1+4 is 303.8±1.1 days, making it by far the widest low-mass X-ray binary system known. 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. © 2000 American Institute of Physics.


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