Discovery of optical pulsations in V2116 Ophiuchi/GX 1+4

Abstract

We report the detection of pulsations with $\sim 124$ s period in V2116 Oph, the optical counterpart of the low-mass X-ray binary GX 1+4. The pulsations are sinusoidal with modulation amplitude of up to 4% in blue light and were observed in ten different observing sessions during 1996 April-August using a CCD photometer at the 1.6-m and 0.6-m telescopes of Laboratório Nacional de Astrof\'ısica, in Brazil. The pulsations were also observed with the $UBVRI$ fast photometer. With only one exception the observed optical periods are consistent with those observed by the BATSE instrument on board the Compton Gamma Ray Observatory at the same epoch. There is a definite correlation between the observability of pulsations and the optical brightness of the system: V2116~Oph had $R$ magnitude in the range $15.3-15.5$ when the pulsed signal was detected, and $R=16.0-17.7$ when no pulsations were present. The discovery makes GX 1+4 only the third of $\sim 35$ accretion-powered X-ray pulsars to be firmly detected as a pulsating source in the optical. The presence of flickering and pulsations in V2116 Oph adds strong evidence for an accretion disk scenario in this system. The absolute magnitude of the pulsed component on 1996 May 27 is estimated to be $M_V\sim -1.5$. The implied dimensions for the emitting region are $1.1 R_{\sun}$, $3.2 R_{\sun}$, and $7.0 R_{\sun}$, for black-body spectral distributions with $T=10^5$ K, $2\times 10^4$ K, and $1\times 10^4$ K, respectively.

9 pages, 3 figures in PostScript, latex, accepted for publication on the Astrophysical Journal Letters

Cited by in corpus (15)

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• High-Speed Optical Photometry of the Ultracompact X-ray Binary 4U 1626-67
• Infrared Spectroscopy of Symbiotic Stars. IV. V2116 Ophiuchi/GX 1+4, The Neutron Star Symbiotic
• The Nature of the Hard-X-Ray Emitting Symbiotic Star RT Cru
• Spin period evolution of GX 1+4
• The Orbital Period of the Accreting Pulsar GX1+4
• Fast X-ray transients in the Galactic bulge with the Rossi X-ray Timing Explorer
• Infrared Spectroscopy of GX 1+4/V2116 Oph: Evidence for a Fast Red Giant Wind?
• Correlated radial velocity and X-ray variations in HD 154791/4U 1700+24
• Variability of the symbiotic X-ray binary GX 1+4: Enhanced activity near periastron passage
• RT Cru: a look into the X-ray emission of a peculiar symbiotic star
• K2 & TESS observations of symbiotic X-ray binaries: GX 1+4 and IGR J16194-2810
• SALT observation of X-ray pulse reprocessing in 4U 1626-67
• Telescope performance and image simulations of the balloon-borne coded-mask protoMIRAX experiment
• A Technique for Narrowband Time Series Photometry: the X-ray Star V2116 Oph