SIMBAD references

Context. GX 1+4 belongs to a rare class of X-ray binaries with red giant donors, symbiotic X-ray binaries. It has a history of complicated variability on multiple timescales in the optical light and X-rays. The nature of this variability remains poorly understood.
Aims. We aim to study variability of GX 1+4 on long timescale in X-ray and optical bands.
Methods. We took X-ray observations from the INTEGRAL Soft Gamma-Ray Imager and RXTE All Sky Monitor. Optical observations were made with the INTEGRAL Optical Monitoring Camera.
Results. The variability of GX 1+4 both in optical light and hard X-ray emission (>17keV) is dominated by ∼50-70d quasi-periodic changes. The amplitude of this variability is highest during the periastron passage, while during the potential neutron star eclipse the system is always at minimum. This confirms the 1161d orbital period that has had been proposed for the system based on radial velocity curve. Neither the quasi-periodic variability or the orbital period are detected in soft X-ray emission (1.3-12.2keV), where the binary shows no apparent periodicity.