Discovery of a 4.2 hour X-ray period in GX 9+9

Abstract

view Abstract Citations (19) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a 4.2 Hour X-Ray Period in GX 9+9 Hertz, Paul ; Wood, Kent S. Abstract The low-mass X-ray binary GX 9+9 (4U 1728-16) was observed during September 13-19, 1977, and March 11-17, 1978, with the HEAO A-1 instrument in scanning mode. An algorithm for detecting periodicities in the resulting light curves has been applied; it is based on the Scargle periodogram and takes into account the non-Gaussian nature of the intrinsic source variability. A 4.19 + or - 0.02 hr periodic modulation is detected in the September 1977 data. The folded light curve shows sinusoidal modulation with an amplitude of 3.8 percent. This amplitude is comparable to the 4.6 percent residual intrinsic source variability at all phases of the light curve. The 4.19 hr period is interpreted as the binary period of the system. The lack of eclipses and the sinusoidal light curve imply that the binary system is viewed at a low inclination angle of less than about 63 deg. Light curves of this type may be relatively common among low-mass X-ray binaries, but are difficult to detect without the long observations and high sensitivity possible with HEAO A-1. Publication: The Astrophysical Journal Pub Date: August 1988 DOI: 10.1086/166597 Bibcode: 1988ApJ...331..764H Keywords: Eclipsing Binary Stars; Light Curve; Main Sequence Stars; Neutron Stars; X Ray Binaries; Accretion Disks; Heao 1; Line Spectra; Monte Carlo Method; Random Sampling; Time Measurement; Astrophysics; STARS: INDIVIDUAL ALPHANUMERIC: GX 9; 9; X-RAYS: BINARIES full text sources ADS | data products SIMBAD (5)